The Spring Web model-view-controller (MVC) framework is designed around a DispatcherServlet that dispatches requests to handlers, with configurable handler mappings, view resolution, locale and theme resolution as well as support for uploading files. The default handler is based on the @Controller and @RequestMapping annotations, offering a wide range of flexible handling methods. With the introduction of Spring 3.0, the @Controller mechanism also allows you to create RESTful Web sites and applications, through the @PathVariable annotation and other features. A key design principle in Spring Web MVC and in Spring in general is the Open for extension, closed for modification principle. Some methods in the core classes of Spring Web MVC are marked final. As a developer you cannot override these methods to supply your own behavior. This has not been done arbitrarily, but specifically with this principle in mind. For an explanation of this principle, refer to Expert Spring Web MVC and Web Flow by Seth Ladd and others; specifically see the section "A Look At Design," on page 117 of the first edition. Alternatively, see Bob Martin, The Open-Closed Principle (PDF) You cannot add advice to final methods when you use Spring MVC. For example, you cannot add advice to the AbstractController.setSynchronizeOnSession() method. Refer to for more information on AOP proxies and why you cannot add advice to final methods. In Spring Web MVC you can use any object as a command or form-backing object; you do not need to implement a framework-specific interface or base class. Spring's data binding is highly flexible: for example, it treats type mismatches as validation errors that can be evaluated by the application, not as system errors. Thus you need not duplicate your business objects' properties as simple, untyped strings in your form objects simply to handle invalid submissions, or to convert the Strings properly. Instead, it is often preferable to bind directly to your business objects. Spring's view resolution is extremely flexible. A Controller is typically responsible for preparing a model Map with data and selecting a view name but it can also write directly to the response stream and complete the request. View name resolution is highly configurable through file extension or Accept header content type negotiation, through bean names, a properties file, or even a custom ViewResolver implementation. The model (the M in MVC) is a Map interface, which allows for the complete abstraction of the view technology. You can integrate directly with template based rendering technologies such as JSP, Velocity and Freemarker, or directly generate XML, JSON, Atom, and many other types of content. The model Map is simply transformed into an appropriate format, such as JSP request attributes, a Velocity template model.

Spring's web module includes many unique web support features: Clear separation of roles. Each role — controller, validator, command object, form object, model object, DispatcherServlet, handler mapping, view resolver, and so on — can be fulfilled by a specialized object. Powerful and straightforward configuration of both framework and application classes as JavaBeans. This configuration capability includes easy referencing across contexts, such as from web controllers to business objects and validators. Adaptability, non-intrusiveness, and flexibility. Define any controller method signature you need, possibly using one of the parameter annotations (such as @RequestParam, @RequestHeader, @PathVariable, and more) for a given scenario. Reusable business code, no need for duplication. Use existing business objects as command or form objects instead of mirroring them to extend a particular framework base class. Customizable binding and validation. Type mismatches as application-level validation errors that keep the offending value, localized date and number binding, and so on instead of String-only form objects with manual parsing and conversion to business objects. Customizable handler mapping and view resolution. Handler mapping and view resolution strategies range from simple URL-based configuration, to sophisticated, purpose-built resolution strategies. Spring is more flexible than web MVC frameworks that mandate a particular technique. Flexible model transfer. Model transfer with a name/value Map supports easy integration with any view technology. Customizable locale and theme resolution, support for JSPs with or without Spring tag library, support for JSTL, support for Velocity without the need for extra bridges, and so on. A simple yet powerful JSP tag library known as the Spring tag library that provides support for features such as data binding and themes. The custom tags allow for maximum flexibility in terms of markup code. For information on the tag library descriptor, see the appendix entitled A JSP form tag library, introduced in Spring 2.0, that makes writing forms in JSP pages much easier. For information on the tag library descriptor, see the appendix entitled Beans whose lifecycle is scoped to the current HTTP request or HTTP Session. This is not a specific feature of Spring MVC itself, but rather of the WebApplicationContext container(s) that Spring MVC uses. These bean scopes are described in

Non-Spring MVC implementations are preferable for some projects. Many teams expect to leverage their existing investment in skills and tools. A large body of knowledge and experience exist for the Struts framework. If you can abide Struts' architectural flaws, it can be a viable choice for the web layer; the same applies to WebWork and other web MVC frameworks. If you do not want to use Spring's web MVC, but intend to leverage other solutions that Spring offers, you can integrate the web MVC framework of your choice with Spring easily. Simply start up a Spring root application context through its ContextLoaderListener, and access it through its ServletContext attribute (or Spring's respective helper method) from within a Struts or WebWork action. No "plug-ins" are involved, so no dedicated integration is necessary. From the web layer's point of view, you simply use Spring as a library, with the root application context instance as the entry point. Your registered beans and Spring's services can be at your fingertips even without Spring's Web MVC. Spring does not compete with Struts or WebWork in this scenario. It simply addresses the many areas that the pure web MVC frameworks do not, from bean configuration to data access and transaction handling. So you can enrich your application with a Spring middle tier and/or data access tier, even if you just want to use, for example, the transaction abstraction with JDBC or Hibernate.

Spring's web MVC framework is, like many other web MVC frameworks, request-driven, designed around a central Servlet that dispatches requests to controllers and offers other functionality that facilitates the development of web applications. Spring's DispatcherServlet however, does more than just that. It is completely integrated with the Spring IoC container and as such allows you to use every other feature that Spring has. The request processing workflow of the Spring Web MVC DispatcherServlet is illustrated in the following diagram. The pattern-savvy reader will recognize that the DispatcherServlet is an expression of the Front Controller design pattern (this is a pattern that Spring Web MVC shares with many other leading web frameworks). The request processing workflow in Spring Web MVC (high level) The DispatcherServlet is an actual Servlet (it inherits from the HttpServlet base class), and as such is declared in the web.xml of your web application. You need to map requests that you want the DispatcherServlet to handle, by using a URL mapping in the same web.xml file. This is standard J2EE Servlet configuration; the following example shows such a DispatcherServlet declaration and mapping: <web-app> <servlet> <servlet-name>example</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>example</servlet-name> <url-pattern>/example/*</url-pattern> </servlet-mapping> </web-app> In the preceding example, all requests startig with /example will be handled by the DispatcherServlet instance named example. This is only the first step in setting up Spring Web MVC. You now need to configure the various beans used by the Spring Web MVC framework (over and above the DispatcherServlet itself). As detailed in , ApplicationContext instances in Spring can be scoped. In the Web MVC framework, each DispatcherServlet has its own WebApplicationContext, which inherits all the beans already defined in the root WebApplicationContext. These inherited beans can be overridden in the servlet-specific scope, and you can define new scope-specific beans local to a given Servlet instance. Context hierarchy in Spring Web MVC Upon initialization of a DispatcherServlet, the framework looks for a file named [servlet-name]-servlet.xml in the WEB-INF directory of your web application and creates the beans defined there, overriding the definitions of any beans defined with the same name in the global scope. Consider the following DispatcherServlet Servlet configuration (in the web.xml file): <web-app> <servlet> <servlet-name>golfing</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>golfing</servlet-name> <url-pattern>/golfing/*</url-pattern> </servlet-mapping> </web-app> With the above Servlet configuration in place, you will need to have a file called /WEB-INF/golfing-servlet.xml in your application; this file will contain all of your Spring Web MVC-specific components (beans). You can change the exact location of this configuration file through a Servlet initialization parameter (see below for details). The WebApplicationContext is an extension of the plain ApplicationContext that has some extra features necessary for web applications. It differs from a normal ApplicationContext in that it is capable of resolving themes (see ), and that it knows which Servlet it is associated with (by having a link to the ServletContext). The WebApplicationContext is bound in the ServletContext, and by using static methods on the RequestContextUtils class you can always look up the WebApplicationContext if you need access to it. The Spring DispatcherServlet uses special beans to process requests and render the appropriate views. These beans are part of Spring Framework. You can configure them in the WebApplicationContext, just as you configure any other bean. However, for most beans, sensible defaults are provided so you initially do not need to configure them. These beans are described in the following table. Bean type Explanation controllers Form the C part of the MVC. handler mappings Handle the execution of a list of pre-processors and post-processors and controllers that will be executed if they match certain criteria (for example, a matching URL specified with the controller). view resolvers Resolves view names to views. locale resolver A locale resolver is a component capable of resolving the locale a client is using, in order to be able to offer internationalized views Theme resolver A theme resolver is capable of resolving themes your web application can use, for example, to offer personalized layouts multipart file resolver Contains functionality to process file uploads from HTML forms. handler exception resolvers Contains functionality to map exceptions to views or implement other more complex exception handling code. After you set up a DispatcherServlet, and a request comes in for that specific DispatcherServlet, the DispatcherServlet starts processing the request as follows: The WebApplicationContext is searched for and bound in the request as an attribute that the controller and other elements in the process can use. It is bound by default under the key DispatcherServlet.WEB_APPLICATION_CONTEXT_ATTRIBUTE. The locale resolver is bound to the request to enable elements in the process to resolve the locale to use when processing the request (rendering the view, preparing data, and so on). If you do not need locale resolving, you do not need it. The theme resolver is bound to the request to let elements such as views determine which theme to use. If you do not use themes, you can ignore it. If you specify a multipart file resolver, the request is inspected for multiparts; if multiparts are found, the request is wrapped in a MultipartHttpServletRequest for further processing by other elements in the process. See for further information about multipart handling. An appropriate handler is searched for. If a handler is found, the execution chain associated with the handler (preprocessors, postprocessors, and controllers) is executed in order to prepare a model or rendering. If a model is returned, the view is rendered. If no model is returned, (may be due to a preprocessor or postprocessor intercepting the request, perhaps for security reasons), no view is rendered, because the request could already have been fulfilled. Handler exception resolvers that are declared in the WebApplicationContext pick up exceptions that are thrown during processing of the request. Using these exception resolvers allows you to define custom behaviors to address exceptions. The Spring DispatcherServlet also supports the return of the last-modification-date, as specified by the Servlet API. The process of determining the last modification date for a specific request is straightforward: the DispatcherServlet looks up an appropriate handler mapping and tests whether the handler that is found implements the LastModified interface. If so, the value of the long getLastModified(request) method of the LastModified interface is returned to the client. You can customize individual DispatcherServlet instances by adding Servlet initialization parameters (init-param elements) to the Servlet declaration in the web.xml file. See the following table for the list of supported parameters. Parameter Explanation contextClass Class that implements WebApplicationContext, which instantiates the context used by this Servlet. By default, the XmlWebApplicationContext is used. contextConfigLocation String that is passed to the context instance (specified by contextClass) to indicate where context(s) can be found. The string consists potentially of multiple strings (using a comma as a delimiter) to support multiple contexts. In case of multiple context locations with beans that are defined twice, the latest location takes precedence. namespace Namespace of the WebApplicationContext. Defaults to [servlet-name]-servlet.

Controllers provide access to the application behavior that you typically define through a service interface. Controllers interpret user input and transform it into a model that is represented to the user by the view. Spring implements a controller in a very abstract way, which enables you to create a wide variety of controllers. Spring 2.5 introduced an annotation-based programming model for MVC controllers that uses annotations such as @RequestMapping, @RequestParam, @ModelAttribute, and so on. This annotation support is available for both Servlet MVC and Portlet MVC. Controllers implemented in this style do not have to extend specific base classes or implement specific interfaces. Furthermore, they do not usually have direct dependencies on Servlet or Portlet APIs, although you can easily configure access to Servlet or Portlet facilities. Available in the samples repository, a number of web applications leverage the annotation support described in this section including MvcShowcase, MvcAjax, MvcBasic, PetClinic, PetCare, and others. @Controller public class HelloWorldController { @RequestMapping("/helloWorld") public String helloWorld(Model model) { model.addAttribute("message", "Hello World!"); return "helloWorld"; } } As you can see, the @Controller and @RequestMapping annotations allow flexible method names and signatures. In this particular example the method accepts a Model and returns a view name as a String, but various other method parameters and return values can be used as explained later in this section. @Controller and @RequestMapping and a number of other annotations form the basis for the Spring MVC implementation. This section documents these annotations and how they are most commonly used in a Servlet environment.

The @Controller annotation indicates that a particular class serves the role of a controller. Spring does not require you to extend any controller base class or reference the Servlet API. However, you can still reference Servlet-specific features if you need to. The @Controller annotation acts as a stereotype for the annotated class, indicating its role. The dispatcher scans such annotated classes for mapped methods and detects @RequestMapping annotations (see the next section). You can define annotated controller beans explicitly, using a standard Spring bean definition in the dispatcher's context. However, the @Controller stereotype also allows for autodetection, aligned with Spring general support for detecting component classes in the classpath and auto-registering bean definitions for them. To enable autodetection of such annotated controllers, you add component scanning to your configuration. Use the spring-context schema as shown in the following XML snippet: <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd"> <context:component-scan base-package="org.springframework.samples.petclinic.web"/> <!-- ... --> </beans>

You use the @RequestMapping annotation to map URLs such as /appointments onto an entire class or a particular handler method. Typically the class-level annotation maps a specific request path (or path pattern) onto a form controller, with additional method-level annotations narrowing the primary mapping for a specific HTTP method request method ("GET", "POST", etc.) or an HTTP request parameter condition. The following example from the Petcare sample shows a controller in a Spring MVC application that uses this annotation: @Controller @RequestMapping("/appointments") public class AppointmentsController { private final AppointmentBook appointmentBook; @Autowired public AppointmentsController(AppointmentBook appointmentBook) { this.appointmentBook = appointmentBook; } @RequestMapping(method = RequestMethod.GET) public Map<String, Appointment> get() { return appointmentBook.getAppointmentsForToday(); } @RequestMapping(value="/{day}", method = RequestMethod.GET) public Map<String, Appointment> getForDay(@PathVariable @DateTimeFormat(iso=ISO.DATE) Date day, Model model) { return appointmentBook.getAppointmentsForDay(day); } @RequestMapping(value="/new", method = RequestMethod.GET) public AppointmentForm getNewForm() { return new AppointmentForm(); } @RequestMapping(method = RequestMethod.POST) public String add(@Valid AppointmentForm appointment, BindingResult result) { if (result.hasErrors()) { return "appointments/new"; } appointmentBook.addAppointment(appointment); return "redirect:/appointments"; } } In the example, the @RequestMapping is used in a number of places. The first usage is on the type (class) level, which indicates that all handling methods on this controller are relative to the /appointments path. The get() method has a further @RequestMapping refinement: it only accepts GET requests, meaning that an HTTP GET for /appointments invokes this method. The post() has a similar refinement, and the getNewForm() combines the definition of HTTP method and path into one, so that GET requests for appointments/new are handled by that method. The getForDay() method shows another usage of @RequestMapping: URI templates. (See the next section ). A @RequestMapping on the class level is not required. Without it, all paths are simply absolute, and not relative. The following example from the PetClinic sample application shows a multi-action controller using @RequestMapping: @Controller public class ClinicController { private final Clinic clinic; @Autowired public ClinicController(Clinic clinic) { this.clinic = clinic; } @RequestMapping("/") public void welcomeHandler() { } @RequestMapping("/vets") public ModelMap vetsHandler() { return new ModelMap(this.clinic.getVets()); } } A common pitfall when working with annotated controller classes happens when applying functionality that requires creating a proxy for the controller object (e.g. @Transactional methods). Usually you will introduce an interface for the controller in order to use JDK dynamic proxies. To make this work you must move the @RequestMapping annotations to the interface as well as the mapping mechanism can only "see" the interface exposed by the proxy. Alternatively, you could activate proxy-target-class="true" in the configuration for the functionality applied to the controller (in our transaction scenario in <tx:annotation-driven />). Doing so indicates that CGLIB-based subclass proxies should be used instead of interface-based JDK proxies. For more information on various proxying mechanisms see .

URI templates can be used for convenient access to selected parts of a URL in a @RequestMapping method. A URI Template is a URI-like string, containing one or more variable names. When you substitute values for these variables, the template becomes a URI. The proposed RFC for URI Templates defines how a URI is parameterized. For example, the URI Template http://www.example.com/users/{userId} contains the variable userId. Assigning the value fred to the variable yields http://www.example.com/users/fred. In Spring MVC you can use the @PathVariable annotation on a method argument to bind it to the value of a URI template variable: @RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET) public String findOwner(@PathVariable String ownerId, Model model) { Owner owner = ownerService.findOwner(ownerId); model.addAttribute("owner", owner); return "displayOwner"; } The URI Template "/owners/{ownerId}" specifies the variable name ownerId. When the controller handles this request, the value of ownerId is set to the value found in the appropriate part of the URI. For example, when a request comes in for /owners/fred, the value of ownerId is fred. To process the @PathVariable annotation, Spring MVC needs to find the matching URI template variable by name. You can specify it in the annotation: @RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET) public String findOwner(@PathVariable("ownerId") String theOwner, Model model) { // implementation omitted } Or if the URI template variable name matches the method argument name you can omit that detail. As long as your code is not compiled without debugging information, Spring MVC will match the method argument name to the URI template variable name: @RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET) public String findOwner(@PathVariable String ownerId, Model model) { // implementation omitted } A method can have any number of @PathVariable annotations: @RequestMapping(value="/owners/{ownerId}/pets/{petId}", method=RequestMethod.GET) public String findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) { Owner owner = ownerService.findOwner(ownerId); Pet pet = owner.getPet(petId); model.addAttribute("pet", pet); return "displayPet"; } A URI template can be assembled from type and path level @RequestMapping annotations. As a result the findPet() method can be invoked with a URL such as /owners/42/pets/21. @Controller @RequestMapping("/owners/{ownerId}") public class RelativePathUriTemplateController { @RequestMapping("/pets/{petId}") public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) { // implementation omitted } } A @PathVariable argument can be of any simple type such as int, long, Date, etc. Spring automatically converts to the appropriate type or throws a TypeMismatchException if it fails to do so. You can also register support for parsing additional data types. See and .

Sometimes you need more precision in defining URI template variables. Consider the URL "/spring-web/spring-web-3.0.5.jar". How do you break it down into multiple parts? The @RequestMapping annotation supports the use of regular expressions in URI template variables. The syntax is {varName:regex} where the first part defines the variable name and the second - the regular expression.For example: @RequestMapping("/spring-web/{symbolicName:[a-z-]+}-{version:\d\.\d\.\d}.{extension:\.[a-z]}") public void handle(@PathVariable String version, @PathVariable String extension) { // ... } }

In addition to URI templates, the @RequestMapping annotation also supports Ant-style path patterns (for example, /myPath/*.do). A combination of URI templates and Ant-style globs is also supported (for example, /owners/*/pets/{petId}).

You can narrow the primary mapping by specifying a list of consumable media types. The request will be matched only if the Content-Type request header matches the specified media type. For example: @Controller @RequestMapping(value = "/pets", method = RequestMethod.POST, consumes="application/json") public void addPet(@RequestBody Pet pet, Model model) { // implementation omitted } Consumable media type expressions can also be negated as in !text/plain to match to all requests other than those with Content-Type of text/plain. The consumes condition is supported on the type and on the method level. Unlike most other conditions, when used at the type level, method-level consumable types override rather than extend type-level consumeable types.

You can narrow the primary mapping by specifying a list of producible media types. The request will be matched only if the Accept request header matches one of these values. Furthermore, use of the produces condition ensures the actual content type used to generate the response respects the media types specified in the produces condition. For example: @Controller @RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET, produces="application/json") @ResponseBody public Pet getPet(@PathVariable String petId, Model model) { // implementation omitted } Just like with consumes, producible media type expressions can be negated as in !text/plain to match to all requests other than those with an Accept header value of text/plain. The produces condition is supported on the type and on the method level. Unlike most other conditions, when used at the type level, method-level producible types override rather than extend type-level producible types.

You can narrow request matching through request parameter conditions such as "myParam", "!myParam", or "myParam=myValue". The first two test for request parameter presense/absence and the third for a specific parameter value. Here is an example with a request parameter value condition: @Controller @RequestMapping("/owners/{ownerId}") public class RelativePathUriTemplateController { @RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET, params="myParam=myValue") public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) { // implementation omitted } } The same can be done to test for request header presence/absence or to match based on a specific request header value: @Controller @RequestMapping("/owners/{ownerId}") public class RelativePathUriTemplateController { @RequestMapping(value = "/pets", method = RequestMethod.GET, headers="myHeader=myValue") public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) { // implementation omitted } } Although you can match to Content-Type and Accept header values using media type wild cards (for example "content-type=text/*" will match to "text/plain" and "text/html"), it is recommended to use the consumes and produces conditions respectively instead. They are intended specifically for that purpose.

An @RequestMapping handler method can have a very flexible signatures. The supported method arguments and return values are described in the following section. Most arguments can be used in arbitrary order with the only exception of BindingResult arguments. This is described in the next section.

The following are the supported method arguments: Request or response objects (Servlet API). Choose any specific request or response type, for example ServletRequest or HttpServletRequest. Session object (Servlet API): of type HttpSession. An argument of this type enforces the presence of a corresponding session. As a consequence, such an argument is never null. Session access may not be thread-safe, in particular in a Servlet environment. Consider setting the AnnotationMethodHandlerAdapter's "synchronizeOnSession" flag to "true" if multiple requests are allowed to access a session concurrently. org.springframework.web.context.request.WebRequest or org.springframework.web.context.request.NativeWebRequest. Allows for generic request parameter access as well as request/session attribute access, without ties to the native Servlet/Portlet API. java.util.Locale for the current request locale, determined by the most specific locale resolver available, in effect, the configured LocaleResolver in a Servlet environment. java.io.InputStream / java.io.Reader for access to the request's content. This value is the raw InputStream/Reader as exposed by the Servlet API. java.io.OutputStream / java.io.Writer for generating the response's content. This value is the raw OutputStream/Writer as exposed by the Servlet API. java.security.Principal containing the currently authenticated user. @PathVariable annotated parameters for access to URI template variables. See . @RequestParam annotated parameters for access to specific Servlet request parameters. Parameter values are converted to the declared method argument type. See . @RequestHeader annotated parameters for access to specific Servlet request HTTP headers. Parameter values are converted to the declared method argument type. @RequestBody annotated parameters for access to the HTTP request body. Parameter values are converted to the declared method argument type using HttpMessageConverters. See . @RequestPart annotated parameters for access to the content of a "multipart/form-data" request part. See and . HttpEntity<?> parameters for access to the Servlet request HTTP headers and contents. The request stream will be converted to the entity body using HttpMessageConverters. See . java.util.Map / org.springframework.ui.Model / org.springframework.ui.ModelMap for enriching the implicit model that is exposed to the web view. org.springframework.web.servlet.mvc.support.RedirectAttributes to specify the exact set of attributes to use in case of a redirect and also to add flash attributes (attributes stored temporarily on the server-side to make them available to the request after the redirect). RedirectAttributes is used instead of the implicit model if the method returns a "redirect:" prefixed view name or RedirectView. Command or form objects to bind request parameters to bean properties (via setters) or directly to fields, with customizable type conversion, depending on @InitBinder methods and/or the HandlerAdapter configuration. See the webBindingInitializer property on RequestMappingHandlerAdapter. Such command objects along with their validation results will be exposed as model attributes by default, using the command class class name - e.g. model attribute "orderAddress" for a command object of type "some.package.OrderAddress". The ModelAttribute annotation can be used on a method argument to customize the model attribute name used. org.springframework.validation.Errors / org.springframework.validation.BindingResult validation results for a preceding command or form object (the immediately preceding method argument). org.springframework.web.bind.support.SessionStatus status handle for marking form processing as complete, which triggers the cleanup of session attributes that have been indicated by the @SessionAttributes annotation at the handler type level. The Errors or BindingResult parameters have to follow the model object that is being bound immediately as the method signature might have more that one model object and Spring will create a separate BindingResult instance for each of them so the following sample won't work: @RequestMapping(method = RequestMethod.POST) public String processSubmit(@ModelAttribute("pet") Pet pet, Model model, BindingResult result) { … } Note, that there is a Model parameter in between Pet and BindingResult. To get this working you have to reorder the parameters as follows: @RequestMapping(method = RequestMethod.POST) public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result, Model model) { … }

The following are the supported return types: A ModelAndView object, with the model implicitly enriched with command objects and the results of @ModelAttribute annotated reference data accessor methods. A Model object, with the view name implicitly determined through a RequestToViewNameTranslator and the model implicitly enriched with command objects and the results of @ModelAttribute annotated reference data accessor methods. A Map object for exposing a model, with the view name implicitly determined through a RequestToViewNameTranslator and the model implicitly enriched with command objects and the results of @ModelAttribute annotated reference data accessor methods. A View object, with the model implicitly determined through command objects and @ModelAttribute annotated reference data accessor methods. The handler method may also programmatically enrich the model by declaring a Model argument (see above). A String value that is interpreted as the logical view name, with the model implicitly determined through command objects and @ModelAttribute annotated reference data accessor methods. The handler method may also programmatically enrich the model by declaring a Model argument (see above). void if the method handles the response itself (by writing the response content directly, declaring an argument of type ServletResponse / HttpServletResponse for that purpose) or if the view name is supposed to be implicitly determined through a RequestToViewNameTranslator (not declaring a response argument in the handler method signature). If the method is annotated with @ResponseBody, the return type is written to the response HTTP body. The return value will be converted to the declared method argument type using HttpMessageConverters. See . A HttpEntity<?> or ResponseEntity<?> object to provide access to the Servlet response HTTP headers and contents. The entity body will be converted to the response stream using HttpMessageConverters. See . Any other return type is considered to be a single model attribute to be exposed to the view, using the attribute name specified through @ModelAttribute at the method level (or the default attribute name based on the return type class name). The model is implicitly enriched with command objects and the results of @ModelAttribute annotated reference data accessor methods.

Use the @RequestParam annotation to bind request parameters to a method parameter in your controller. The following code snippet shows the usage: @Controller @RequestMapping("/pets") @SessionAttributes("pet") public class EditPetForm { // ... @RequestMapping(method = RequestMethod.GET) public String setupForm(@RequestParam("petId") int petId, ModelMap model) { Pet pet = this.clinic.loadPet(petId); model.addAttribute("pet", pet); return "petForm"; } // ... Parameters using this annotation are required by default, but you can specify that a parameter is optional by setting @RequestParam's required attribute to false (e.g., @RequestParam(value="id", required=false)). Type conversion is applied automatically if the target method parameter type is not String. See .

The @RequestBody method parameter annotation indicates that a method parameter should be bound to the value of the HTTP request body. For example: @RequestMapping(value = "/something", method = RequestMethod.PUT) public void handle(@RequestBody String body, Writer writer) throws IOException { writer.write(body); } You convert the request body to the method argument by using an HttpMessageConverter. HttpMessageConverter is responsible for converting from the HTTP request message to an object and converting from an object to the HTTP response body. The RequestMappingHandlerAdapter supports the @RequestBody annotation with the following default HttpMessageConverters: ByteArrayHttpMessageConverter converts byte arrays. StringHttpMessageConverter converts strings. FormHttpMessageConverter converts form data to/from a MultiValueMap<String, String>. SourceHttpMessageConverter converts to/from a javax.xml.transform.Source. For more information on these converters, see Message Converters. Also note that if using the MVC namespace, a wider range of message converters are registered by default. See for more information. If you intend to read and write XML, you will need to configure the MarshallingHttpMessageConverter with a specific Marshaller and an Unmarshaller implementation from the org.springframework.oxm package. For example: <bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter"> <property name="messageConverters"> <util:list id="beanList"> <ref bean="stringHttpMessageConverter"/> <ref bean="marshallingHttpMessageConverter"/> </util:list> </property </bean> <bean id="stringHttpMessageConverter" class="org.springframework.http.converter.StringHttpMessageConverter"/> <bean id="marshallingHttpMessageConverter" class="org.springframework.http.converter.xml.MarshallingHttpMessageConverter"> <property name="marshaller" ref="castorMarshaller" /> <property name="unmarshaller" ref="castorMarshaller" /> </bean> <bean id="castorMarshaller" class="org.springframework.oxm.castor.CastorMarshaller"/> An @RequestBody method parameter can be annotated with @Valid, in which case it will validated using the configured Validator instance. When using the MVC namespace a JSR-303 validator is configured automatically assuming a JSR-303 implementation is available on the classpath. If validation fails a RequestBodyNotValidException is raised. The exception is handled by the DefaultHandlerExceptionResolver and results in a 400 error sent back to the client along with a message containing the validation errors. Also see for information on configuring message converters and a validator through the MVC namespace.

The @ResponseBody annotation is similar to @RequestBody. This annotation can be put on a method and indicates that the return type should be written straight to the HTTP response body (and not placed in a Model, or interpreted as a view name). For example: @RequestMapping(value = "/something", method = RequestMethod.PUT) @ResponseBody public String helloWorld() { return "Hello World"; } The above example will result in the text Hello World being written to the HTTP response stream. As with @RequestBody, Spring converts the returned object to a response body by using an HttpMessageConverter. For more information on these converters, see the previous section and Message Converters.

The HttpEntity is similar to @RequestBody and @ResponseBody. Besides getting access to the request and response body, HttpEntity (and the response-specific subclass ResponseEntity) also allows access to the request and response headers, like so: @RequestMapping("/something") public ResponseEntity<String> handle(HttpEntity<byte[]> requestEntity) throws UnsupportedEncodingException { String requestHeader = requestEntity.getHeaders().getFirst("MyRequestHeader")); byte[] requestBody = requestEntity.getBody(); // do something with request header and body HttpHeaders responseHeaders = new HttpHeaders(); responseHeaders.set("MyResponseHeader", "MyValue"); return new ResponseEntity<String>("Hello World", responseHeaders, HttpStatus.CREATED); } The above example gets the value of the MyRequestHeader request header, and reads the body as a byte array. It adds the MyResponseHeader to the response, writes Hello World to the response stream, and sets the response status code to 201 (Created). As with @RequestBody and @ResponseBody, Spring uses HttpMessageConverter to convert from and to the request and response streams. For more information on these converters, see the previous section and Message Converters.

The @ModelAttribute annotation can be used on methods or on method arguments. This section explains its usage on methods while the next section explains its usage on method arguments. An @ModelAttribute on a method indicates the purpose of that method is to add one or more model attributes. Such methods support the same argument types as @RequestMapping methods but cannot be mapped directly to requests. Instead @ModelAttribute methods in a controller are invoked before @RequestMapping methods, within the same controller. A couple of examples: // Add one attribute // The return value of the method is added to the model under the name "account" // You can customize the name via @ModelAttribute("myAccount") @ModelAttribute public Account addAccount(@RequestParam String number) { return accountManager.findAccount(number); } // Add multiple attributes @ModelAttribute public void populateModel(@RequestParam String number, Model model) { model.addAttribute(accountManager.findAccount(number)); // add more ... } @ModelAttribute methods are used to populate the model with commonly needed attributes for example to fill a drop-down with states or with pet types, or to retrieve a command object like Account in order to use it to represent the data on an HTML form. The latter case is further discussed in the next section. Note the two styles of @ModelAttribute methods. In the first, the method adds an attribute implicitly by returning it. In the second, the method accepts a Model and adds any number of model attributes to it. You can choose between the two styles depending on your needs. A controller can have any number of @ModelAttribute methods. All such methods are invoked before @RequestMapping methods of the same controller. What happens when a model attribute name is not explicitly specified? In such cases a default name is assigned to the model attribute based on its type. For example if the method returns an object of type Account, the default name used is "account". You can change that through the value of the @ModelAttribute annotation. If adding attributes directly to the Model, use the appropriate overloaded addAttribute(..) method - i.e., with or without an attribute name. The @ModelAttribute annotation can be used on @RequestMapping methods as well. In that case the return value of the @RequestMapping method is interpreted as a model attribute rather than as a view name. The view name is derived from view name conventions instead much like for methods returning void — see .

As explained in the previous section @ModelAttribute can be used on methods or on method arguments. This section explains its usage on method arguments. An @ModelAttribute on a method argument indicates the argument should be retrieved from the model. If not present in the model, the argument should be instantiated first and then added to the model. Once present in the model, the argument's fields should be populated from all request parameters that have matching names. This is known as data binding in Spring MVC, a very useful mechanism that saves you from having to parse each form field individually. @RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST) public String processSubmit(@ModelAttribute Pet pet) { } Given the above example where can the Pet instance come from? There are several options: It may already be in the model due to use of @SessionAttributes — see . It may already be in the model due to an @ModelAttribute method in the same controller — as explained in the previous section. It may be retrieved based on a URI template variable and type converter (explained in more detail below). It may be instantiated using its default constructor. An @ModelAttribute method is a common way to to retrieve an attribute from the database, which may optionally be stored between requests through the use of @SessionAttributes. In some cases it may be convenient to retrieve the attribute by using an URI template variable and a type converter. Here is an example: @RequestMapping(value="/accounts/{account}", method = RequestMethod.PUT) public String save(@ModelAttribute("account") Account account) { } In this example the name of the model attribute (i.e. "account") matches the name of a URI template variable. If you register Converter<String, Account> that can turn the String account value into an Account instance, then the above example will work without the need for an @ModelAttribute method. The next step is data binding. The WebDataBinder class matches request parameter names — including query string parameters and form fields — to model attribute fields by name. Matching fields are populated after type conversion (from String to the target field type) has been applied where necessary. Data binding and validation are covered in . Customizing the data binding process for a controller level is covered in . As a result of data binding there may be errors such as missing required fields or type conversion errors. To check for such errors add a BindingResult argument immediately following the @ModelAttribute argument: @RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST) public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result) { if (result.hasErrors()) { return "petForm"; } // ... } With a BindingResult you can check if errors were found in which case it's common to render the same form where the errors can be shown with the help of Spring's <errors> form tag. In addition to data binding you can also invoke validation using your own custom validator passing the same BindingResult that was used to record data binding errors. That allows for data binding and validation errors to be accumulated in one place and subsequently reported back to the user: @RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST) public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result) { new PetValidator().validate(pet, result); if (result.hasErrors()) { return "petForm"; } // ... } Or you can have validation invoked automatically by adding the JSR-303 @Valid annotation: @RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST) public String processSubmit(@Valid @ModelAttribute("pet") Pet pet, BindingResult result) { if (result.hasErrors()) { return "petForm"; } // ... } See and for details on how to configure and use validation.

The type-level @SessionAttributes annotation declares session attributes used by a specific handler. This will typically list the names of model attributes or types of model attributes which should be transparently stored in the session or some conversational storage, serving as form-backing beans between subsequent requests. The following code snippet shows the usage of this annotation, specifying the model attribute name: @Controller @RequestMapping("/editPet.do") @SessionAttributes("pet") public class EditPetForm { // ... } When using controller interfaces (e.g., for AOP proxying), make sure to consistently put all your mapping annotations - such as @RequestMapping and @SessionAttributes - on the controller interface rather than on the implementation class.

By default all model attributes are considered to be exposed as URI template variables in the redirect URL. Of the remaining attributes those that are primitive types or collections/arrays of primitive types are automatically appended as query parameters. In annotated controllers however the model may contain additional attributes originally added for rendering purposes (e.g. drop-down field values). To gain precise control over the attributes used in a redirect scenario, an @RequestMapping method can declare an argument of type RedirectAttributes and use it to add attributes for use in RedirectView. If the controller method does redirect, the content of RedirectAttributes is used. Otherwise the content of the default Model is used. The RequestMappingHandlerAdapter provides a flag called "ignoreDefaultModelOnRedirect" that can be used to indicate the content of the default Model should never be used if a controller method redirects. Instead the controller method should declare an attribute of type RedirectAttributes or if it doesn't do so no attributes should be passed on to RedirectView. Both the MVC namespace and the MVC Java config (via @EnableWebMvc) automatically set this flag to true. The RedirectAttributes interface can also be used to add flash attributes. Unlike other redirect attributes, which end up in the target redirect URL, flash attributes are saved in the HTTP session (and hence do not appear in the URL). The model of the controller serving the target redirect URL automatically receives these flash attributes after which they are removed from the session. See for an overview of the general support for flash attributes in Spring MVC.

The previous sections covered use of @ModelAttribute to support form submission requests from browser clients. The same annotation is recommended for use with requests from non-browser clients as well. However there is one notable difference when it comes to working with HTTP PUT requests. Browsers can submit form data via HTTP GET or HTTP POST. Non-browser clients can also submit forms via HTTP PUT. This presents a challenge because the Servlet specification requires the ServletRequest.getParameter*() family of methods to support form field access only for HTTP POST, not for HTTP PUT. To support HTTP PUT requests, the spring-web module provides the filter HttpPutFormContentFilter, which can be configured in web.xml: <filter> <filter-name>httpPutFormFilter</filter-name> <filter-class>org.springframework.web.filter.HttpPutFormContentFilter</filter-class> </filter> <filter-mapping> <filter-name>httpPutFormFilter</filter-name> <servlet-name>dispatcherServlet</servlet-name> </filter-mapping> <servlet> <servlet-name>dispatcherServlet</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> </servlet> The above filter intercepts HTTP PUT requests with content type application/x-www-form-urlencoded, reads the form data from the body of the request, and wraps the ServletRequest in order to make the form data available through the ServletRequest.getParameter*() family of methods.

The @CookieValue annotation allows a method parameter to be bound to the value of an HTTP cookie. Let us consider that the following cookie has been received with an http request: JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84 The following code sample demonstrates how to get the value of the JSESSIONID cookie: @RequestMapping("/displayHeaderInfo.do") public void displayHeaderInfo(@CookieValue("JSESSIONID") String cookie) { //... } Type conversion is applied automatically if the target method parameter type is not String. See . This annotation is supported for annotated handler methods in Servlet and Portlet environments.

The @RequestHeader annotation allows a method parameter to be bound to a request header. Here is a sample request header: Host localhost:8080 Accept text/html,application/xhtml+xml,application/xml;q=0.9 Accept-Language fr,en-gb;q=0.7,en;q=0.3 Accept-Encoding gzip,deflate Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive 300 The following code sample demonstrates how to get the value of the Accept-Encoding and Keep-Alive headers: @RequestMapping("/displayHeaderInfo.do") public void displayHeaderInfo(@RequestHeader("Accept-Encoding") String encoding, @RequestHeader("Keep-Alive") long keepAlive) { //... } Type conversion is applied automatically if the method parameter is not String. See . Built-in support is available for converting a comma-separated string into an array/collection of strings or other types known to the type conversion system. For example a method parameter annotated with @RequestHeader("Accept") may be of type String but also String[] or List<String>. This annotation is supported for annotated handler methods in Servlet and Portlet environments.

String-based values extracted from the request including request parameters, path variables, request headers, and cookie values may need to be converted to the target type of the method parameter or field (e.g., binding a request parameter to a field in an @ModelAttribute parameter) they're bound to. If the target type is not String, Spring automatically converts to the appropriate type. All simple types such as int, long, Date, etc. are supported. You can further customize the conversion process through a WebDataBinder (see ) or by registering Formatters with the FormattingConversionService (see ).

To customize request parameter binding with PropertyEditors through Spring's WebDataBinder, you can use either @InitBinder-annotated methods within your controller or externalize your configuration by providing a custom WebBindingInitializer.

Annotating controller methods with @InitBinder allows you to configure web data binding directly within your controller class. @InitBinder identifies methods that initialize the WebDataBinder that will be used to populate command and form object arguments of annotated handler methods. Such init-binder methods support all arguments that @RequestMapping supports, except for command/form objects and corresponding validation result objects. Init-binder methods must not have a return value. Thus, they are usually declared as void. Typical arguments include WebDataBinder in combination with WebRequest or java.util.Locale, allowing code to register context-specific editors. The following example demonstrates the use of @InitBinder to configure a CustomDateEditor for all java.util.Date form properties. @Controller public class MyFormController { @InitBinder public void initBinder(WebDataBinder binder) { SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd"); dateFormat.setLenient(false); binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, false)); } // ... }

To externalize data binding initialization, you can provide a custom implementation of the WebBindingInitializer interface, which you then enable by supplying a custom bean configuration for an AnnotationMethodHandlerAdapter, thus overriding the default configuration. The following example from the PetClinic application shows a configuration using a custom implementation of the WebBindingInitializer interface, org.springframework.samples.petclinic.web.ClinicBindingInitializer, which configures PropertyEditors required by several of the PetClinic controllers. <bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter"> <property name="cacheSeconds" value="0" /> <property name="webBindingInitializer"> <bean class="org.springframework.samples.petclinic.web.ClinicBindingInitializer" /> </property> </bean>

An @RequestMapping method may wish to support 'Last-Modified' HTTP requests, as defined in the contract for the Servlet API's getLastModified method, to facilitate content caching. This involves calculating a lastModified long value for a given request, comparing it against the 'If-Modified-Since' request header value, and potentially returning a response with status code 304 (Not Modified). An annotated controller method can achieve that as follows: @RequestMapping public String myHandleMethod(WebRequest webRequest, Model model) { long lastModified = // 1. application-specific calculation if (request.checkNotModified(lastModified)) { // 2. shortcut exit - no further processing necessary return null; } // 3. or otherwise further request processing, actually preparing content model.addAttribute(...); return "myViewName"; } There are two key elements to note: calling request.checkNotModified(lastModified) and returning null. The former sets the response status to 304 before it returns true. The latter, in combination with the former, causes Spring MVC to do no further processing of the request.

In previous versions of Spring, users were required to define one or more HandlerMapping beans in the web application context to map incoming web requests to appropriate handlers. With the introduction of annotated controllers, you generally don't need to do that because the RequestMappingHandlerMapping automatically looks for @RequestMapping annotations on all @Controller beans. However, do keep in mind that all HandlerMapping classes extending from AbstractHandlerMapping have the following properties that you can use to customize their behavior: interceptors List of interceptors to use. HandlerInterceptors are discussed in . defaultHandler Default handler to use, when this handler mapping does not result in a matching handler. order Based on the value of the order property (see the org.springframework.core.Ordered interface), Spring sorts all handler mappings available in the context and applies the first matching handler. alwaysUseFullPath If true , Spring uses the full path within the current Servlet context to find an appropriate handler. If false (the default), the path within the current Servlet mapping is used. For example, if a Servlet is mapped using /testing/* and the alwaysUseFullPath property is set to true, /testing/viewPage.html is used, whereas if the property is set to false, /viewPage.html is used. urlDecode Defaults to true, as of Spring 2.5. If you prefer to compare encoded paths, set this flag to false. However, the HttpServletRequest always exposes the Servlet path in decoded form. Be aware that the Servlet path will not match when compared with encoded paths. The following example shows how to configure an interceptor: <beans> <bean id="handlerMapping" class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping"> <property name="interceptors"> <bean class="example.MyInterceptor"/> </property> </bean> <beans>

Spring's handler mapping mechanism includes handler interceptors, which are useful when you want to apply specific functionality to certain requests, for example, checking for a principal. Interceptors located in the handler mapping must implement HandlerInterceptor from the org.springframework.web.servlet package. This interface defines three methods: preHandle(..) is called before the actual handler is executed; postHandle(..) is called after the handler is executed; and afterCompletion(..) is called after the complete request has finished. These three methods should provide enough flexibility to do all kinds of preprocessing and postprocessing. The preHandle(..) method returns a boolean value. You can use this method to break or continue the processing of the execution chain. When this method returns true, the handler execution chain will continue; when it returns false, the DispatcherServlet assumes the interceptor itself has taken care of requests (and, for example, rendered an appropriate view) and does not continue executing the other interceptors and the actual handler in the execution chain. Interceptors can be configured using the interceptors property, which is present on all HandlerMapping classes extending from AbstractHandlerMapping. This is shown in the example below: <beans> <bean id="handlerMapping" class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping"> <property name="interceptors"> <list> <ref bean="officeHoursInterceptor"/> </list> </property> </bean> <bean id="officeHoursInterceptor" class="samples.TimeBasedAccessInterceptor"> <property name="openingTime" value="9"/> <property name="closingTime" value="18"/> </bean> <beans> package samples; public class TimeBasedAccessInterceptor extends HandlerInterceptorAdapter { private int openingTime; private int closingTime; public void setOpeningTime(int openingTime) { this.openingTime = openingTime; } public void setClosingTime(int closingTime) { this.closingTime = closingTime; } public boolean preHandle( HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { Calendar cal = Calendar.getInstance(); int hour = cal.get(HOUR_OF_DAY); if (openingTime <= hour && hour < closingTime) { return true; } else { response.sendRedirect("http://host.com/outsideOfficeHours.html"); return false; } } } Any request handled by this mapping is intercepted by the TimeBasedAccessInterceptor. If the current time is outside office hours, the user is redirected to a static HTML file that says, for example, you can only access the website during office hours. When using the RequestMappingHandlerMapping the actual handler is an instance of HandlerMethod which identifies the specific controller method that will be invoked. As you can see, the Spring adapter class HandlerInterceptorAdapter makes it easier to extend the HandlerInterceptor interface. In the example above, the configured interceptor will apply to all requests handled with annotated controller methods. If you want to narrow down the URL paths to which an interceptor applies, you can use the MVC namespace to do that. See .

All MVC frameworks for web applications provide a way to address views. Spring provides view resolvers, which enable you to render models in a browser without tying you to a specific view technology. Out of the box, Spring enables you to use JSPs, Velocity templates and XSLT views, for example. See for a discussion of how to integrate and use a number of disparate view technologies. The two interfaces that are important to the way Spring handles views are ViewResolver and View. The ViewResolver provides a mapping between view names and actual views. The View interface addresses the preparation of the request and hands the request over to one of the view technologies.

As discussed in , all handler methods in the Spring Web MVC controllers must resolve to a logical view name, either explicitly (e.g., by returning a String, View, or ModelAndView) or implicitly (i.e., based on conventions). Views in Spring are addressed by a logical view name and are resolved by a view resolver. Spring comes with quite a few view resolvers. This table lists most of them; a couple of examples follow. ViewResolver Description AbstractCachingViewResolver Abstract view resolver that caches views. Often views need preparation before they can be used; extending this view resolver provides caching. XmlViewResolver Implementation of ViewResolver that accepts a configuration file written in XML with the same DTD as Spring's XML bean factories. The default configuration file is /WEB-INF/views.xml. ResourceBundleViewResolver Implementation of ViewResolver that uses bean definitions in a ResourceBundle, specified by the bundle base name. Typically you define the bundle in a properties file, located in the classpath. The default file name is views.properties. UrlBasedViewResolver Simple implementation of the ViewResolver interface that effects the direct resolution of logical view names to URLs, without an explicit mapping definition. This is appropriate if your logical names match the names of your view resources in a straightforward manner, without the need for arbitrary mappings. InternalResourceViewResolver Convenient subclass of UrlBasedViewResolver that supports InternalResourceView (in effect, Servlets and JSPs) and subclasses such as JstlView and TilesView. You can specify the view class for all views generated by this resolver by using setViewClass(..). See the Javadocs for the UrlBasedViewResolver class for details. VelocityViewResolver / FreeMarkerViewResolver Convenient subclass of UrlBasedViewResolver that supports VelocityView (in effect, Velocity templates) or FreeMarkerView ,respectively, and custom subclasses of them. ContentNegotiatingViewResolver Implementation of the ViewResolver interface that resolves a view based on the request file name or Accept header. See . As an example, with JSP as a view technology, you can use the UrlBasedViewResolver. This view resolver translates a view name to a URL and hands the request over to the RequestDispatcher to render the view. <bean id="viewResolver" class="org.springframework.web.servlet.view.UrlBasedViewResolver"> <property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> </bean> When returning test as a logical view name, this view resolver forwards the request to the RequestDispatcher that will send the request to /WEB-INF/jsp/test.jsp. When you combine different view technologies in a web application, you can use the ResourceBundleViewResolver: <bean id="viewResolver" class="org.springframework.web.servlet.view.ResourceBundleViewResolver"> <property name="basename" value="views"/> <property name="defaultParentView" value="parentView"/> </bean> The ResourceBundleViewResolver inspects the ResourceBundle identified by the basename, and for each view it is supposed to resolve, it uses the value of the property [viewname].(class) as the view class and the value of the property [viewname].url as the view url. Examples can be found in the next chapter which covers view technologies. As you can see, you can identify a parent view, from which all views in the properties file extend. This way you can specify a default view class, for example. Subclasses of AbstractCachingViewResolver cache view instances that they resolve. Caching improves performance of certain view technologies. It's possible to turn off the cache by setting the cache property to false. Furthermore, if you must refresh a certain view at runtime (for example when a Velocity template is modified), you can use the removeFromCache(String viewName, Locale loc) method.

Spring supports multiple view resolvers. Thus you can chain resolvers and, for example, override specific views in certain circumstances. You chain view resolvers by adding more than one resolver to your application context and, if necessary, by setting the order property to specify ordering. Remember, the higher the order property, the later the view resolver is positioned in the chain. In the following example, the chain of view resolvers consists of two resolvers, an InternalResourceViewResolver, which is always automatically positioned as the last resolver in the chain, and an XmlViewResolver for specifying Excel views. Excel views are not supported by the InternalResourceViewResolver. <bean id="jspViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> </bean> <bean id="excelViewResolver" class="org.springframework.web.servlet.view.XmlViewResolver"> <property name="order" value="1"/> <property name="location" value="/WEB-INF/views.xml"/> </bean> <!-- in views.xml --> <beans> <bean name="report" class="org.springframework.example.ReportExcelView"/> </beans> If a specific view resolver does not result in a view, Spring examines the context for other view resolvers. If additional view resolvers exist, Spring continues to inspect them until a view is resolved. If no view resolver returns a view, Spring throws a ServletException. The contract of a view resolver specifies that a view resolver can return null to indicate the view could not be found. Not all view resolvers do this, however, because in some cases, the resolver simply cannot detect whether or not the view exists. For example, the InternalResourceViewResolver uses the RequestDispatcher internally, and dispatching is the only way to figure out if a JSP exists, but this action can only execute once. The same holds for the VelocityViewResolver and some others. Check the Javadoc for the view resolver to see whether it reports non-existing views. Thus, putting an InternalResourceViewResolver in the chain in a place other than the last, results in the chain not being fully inspected, because the InternalResourceViewResolver will always return a view!

As mentioned previously, a controller typically returns a logical view name, which a view resolver resolves to a particular view technology. For view technologies such as JSPs that are processed through the Servlet or JSP engine, this resolution is usually handled through the combination of InternalResourceViewResolver and InternalResourceView, which issues an internal forward or include via the Servlet API's RequestDispatcher.forward(..) method or RequestDispatcher.include() method. For other view technologies, such as Velocity, XSLT, and so on, the view itself writes the content directly to the response stream. It is sometimes desirable to issue an HTTP redirect back to the client, before the view is rendered. This is desirable, for example, when one controller has been called with POSTed data, and the response is actually a delegation to another controller (for example on a successful form submission). In this case, a normal internal forward will mean that the other controller will also see the same POST data, which is potentially problematic if it can confuse it with other expected data. Another reason to perform a redirect before displaying the result is to eliminate the possibility of the user submitting the form data multiple times. In this scenario, the browser will first send an initial POST; it will then receive a response to redirect to a different URL; and finally the browser will perform a subsequent GET for the URL named in the redirect response. Thus, from the perspective of the browser, the current page does not reflect the result of a POST but rather of a GET. The end effect is that there is no way the user can accidentally re-POST the same data by performing a refresh. The refresh forces a GET of the result page, not a resend of the initial POST data.

One way to force a redirect as the result of a controller response is for the controller to create and return an instance of Spring's RedirectView. In this case, DispatcherServlet does not use the normal view resolution mechanism. Rather because it has been given the (redirect) view already, the DispatcherServlet simply instructs the view to do its work. The RedirectView issues an HttpServletResponse.sendRedirect() call that returns to the client browser as an HTTP redirect. By default all model attributes are considered to be exposed as URI template variables in the redirect URL. Of the remaining attributes those that are primitive types or collections/arrays of primitive types are automatically appended as query parameters. Appending primitive type attributes as query parameters may be the desired result if a model instance was prepared specifically for the redirect. However, in annotated controllers the model may contain additional attributes added for rendering purposes (e.g. drop-down field values). To avoid the possibility of having such attributes appear in the URL an annotated controller can declare an argument of type RedirectAttributes and use it to specify the exact attributes to make available to RedirectView. If the controller method decides to redirect, the content of RedirectAttributes is used. Otherwise the content of the model is used. Note that URI template variables from the present request are automatically made available when expanding a redirect URL and do not need to be added explicitly neither through Model nor RedirectAttributes. For example: @RequestMapping(value = "/files/{path}", method = RequestMethod.POST) public String upload(...) { // ... return "redirect:files/{path}"; } If you use RedirectView and the view is created by the controller itself, it is recommended that you configure the redirect URL to be injected into the controller so that it is not baked into the controller but configured in the context along with the view names. The next section discusses this process.

While the use of RedirectView works fine, if the controller itself creates the RedirectView, there is no avoiding the fact that the controller is aware that a redirection is happening. This is really suboptimal and couples things too tightly. The controller should not really care about how the response gets handled. In general it should operate only in terms of view names that have been injected into it. The special redirect: prefix allows you to accomplish this. If a view name is returned that has the prefix redirect:, the UrlBasedViewResolver (and all subclasses) will recognize this as a special indication that a redirect is needed. The rest of the view name will be treated as the redirect URL. The net effect is the same as if the controller had returned a RedirectView, but now the controller itself can simply operate in terms of logical view names. A logical view name such as redirect:/myapp/some/resource will redirect relative to the current Servlet context, while a name such as redirect:http://myhost.com/some/arbitrary/path will redirect to an absolute URL.

It is also possible to use a special forward: prefix for view names that are ultimately resolved by UrlBasedViewResolver and subclasses. This creates an InternalResourceView (which ultimately does a RequestDispatcher.forward()) around the rest of the view name, which is considered a URL. Therefore, this prefix is not useful with InternalResourceViewResolver and InternalResourceView (for JSPs for example). But the prefix can be helpful when you are primarily using another view technology, but still want to force a forward of a resource to be handled by the Servlet/JSP engine. (Note that you may also chain multiple view resolvers, instead.) As with the redirect: prefix, if the view name with the forward: prefix is injected into the controller, the controller does not detect that anything special is happening in terms of handling the response.

The ContentNegotiatingViewResolver does not resolve views itself but rather delegates to other view resolvers, selecting the view that resembles the representation requested by the client. Two strategies exist for a client to request a representation from the server: Use a distinct URI for each resource, typically by using a different file extension in the URI. For example, the URI http://www.example.com/users/fred.pdf requests a PDF representation of the user fred, and http://www.example.com/users/fred.xml requests an XML representation. Use the same URI for the client to locate the resource, but set the Accept HTTP request header to list the media types that it understands. For example, an HTTP request for http://www.example.com/users/fred with an Accept header set to application/pdf requests a PDF representation of the user fred, while http://www.example.com/users/fred with an Accept header set to text/xml requests an XML representation. This strategy is known as content negotiation. One issue with the Accept header is that it is impossible to set it in a web browser within HTML. For example, in Firefox, it is fixed to: Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 For this reason it is common to see the use of a distinct URI for each representation when developing browser based web applications. To support multiple representations of a resource, Spring provides the ContentNegotiatingViewResolver to resolve a view based on the file extension or Accept header of the HTTP request. ContentNegotiatingViewResolver does not perform the view resolution itself but instead delegates to a list of view resolvers that you specify through the bean property ViewResolvers. The ContentNegotiatingViewResolver selects an appropriate View to handle the request by comparing the request media type(s) with the media type (also known as Content-Type) supported by the View associated with each of its ViewResolvers. The first View in the list that has a compatible Content-Type returns the representation to the client. If a compatible view cannot be supplied by the ViewResolver chain, then the list of views specified through the DefaultViews property will be consulted. This latter option is appropriate for singleton Views that can render an appropriate representation of the current resource regardless of the logical view name. The Accept header may include wild cards, for example text/*, in which case a View whose Content-Type was text/xml is a compatible match. To support the resolution of a view based on a file extension, use the ContentNegotiatingViewResolver bean property mediaTypes to specify a mapping of file extensions to media types. For more information on the algorithm used to determine the request media type, refer to the API documentation for ContentNegotiatingViewResolver. Here is an example configuration of a ContentNegotiatingViewResolver: <bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver"> <property name="mediaTypes"> <map> <entry key="atom" value="application/atom+xml"/> <entry key="html" value="text/html"/> <entry key="json" value="application/json"/> </map> </property> <property name="viewResolvers"> <list> <bean class="org.springframework.web.servlet.view.BeanNameViewResolver"/> <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> </bean> </list> </property> <property name="defaultViews"> <list> <bean class="org.springframework.web.servlet.view.json.MappingJacksonJsonView" /> </list> </property> </bean> <bean id="content" class="com.springsource.samples.rest.SampleContentAtomView"/> The InternalResourceViewResolver handles the translation of view names and JSP pages, while the BeanNameViewResolver returns a view based on the name of a bean. (See "Resolving views with the ViewResolver interface" for more details on how Spring looks up and instantiates a view.) In this example, the content bean is a class that inherits from AbstractAtomFeedView, which returns an Atom RSS feed. For more information on creating an Atom Feed representation, see the section Atom Views. In the above configuration, if a request is made with an .html extension, the view resolver looks for a view that matches the text/html media type. The InternalResourceViewResolver provides the matching view for text/html. If the request is made with the file extension .atom, the view resolver looks for a view that matches the application/atom+xml media type. This view is provided by the BeanNameViewResolver that maps to the SampleContentAtomView if the view name returned is content. If the request is made with the file extension .json, the MappingJacksonJsonView instance from the DefaultViews list will be selected regardless of the view name. Alternatively, client requests can be made without a file extension but with the Accept header set to the preferred media-type, and the same resolution of request to views would occur. If ContentNegotiatingViewResolver's list of ViewResolvers is not configured explicitly, it automatically uses any ViewResolvers defined in the application context. The corresponding controller code that returns an Atom RSS feed for a URI of the form http://localhost/content.atom or http://localhost/content with an Accept header of application/atom+xml is shown below. @Controller public class ContentController { private List<SampleContent> contentList = new ArrayList<SampleContent>(); @RequestMapping(value="/content", method=RequestMethod.GET) public ModelAndView getContent() { ModelAndView mav = new ModelAndView(); mav.setViewName("content"); mav.addObject("sampleContentList", contentList); return mav; } }

Flash attributes provide a way for one request to store attributes intended for use in another. This is most commonly needed when redirecting — for example, the Post/Redirect/Get pattern. Flash attributes are saved temporarily before the redirect (typically in the session) to be made available to the request after the redirect and removed immediately. Spring MVC has two main abstractions in support of flash attributes. FlashMap is used to hold flash attributes while FlashMapManager is used to store, retrieve, and manage FlashMap instances. Flash attribute support is always "on" and does not need to enabled explicitly although if not used, it never causes HTTP session creation. On each request there is an "input" FlashMap with attributes passed from a previous request (if any) and an "output" FlashMap with attributes to save for a subsequent request. Both FlashMap instances are accessible from anywhere in Spring MVC through static methods in RequestContextUtils. Annotated controllers typically do not need to work with FlashMap directly. Instead an @RequestMapping method can accept an argument of type RedirectAttributes and use it to add flash attributes for a redirect scenario. Flash attributes added via RedirectAttributes are automatically propagated to the "output" FlashMap. Similarly after the redirect attributes from the "input" FlashMap are automatically added to the Model of the controller serving the target URL. The concept of flash attributes exists in many other Web frameworks and has proven to be exposed sometimes to concurrency issues. This is because by definition flash attributes are to be stored until the next request. However the very "next" request may not be the intended recipient but another asynchronous request (e.g. polling or resource requests) in which case the flash attributes are removed too early. To reduce the possibility of such issues, RedirectView automatically "stamps" FlashMap instances with the path and query parameters of the target redirect URL. In turn the default FlashMapManager matches that information to incoming requests when looking up the "input" FlashMap. This does not eliminate the possibility of a concurrency issue entirely but nevertheless reduces it greatly with information that is already available in the redirect URL. Therefore the use of flash attributes is recommended mainly for redirect scenarios unless the target URL and/or query parameters are known.

Most parts of Spring's architecture support internationalization, just as the Spring web MVC framework does. DispatcherServlet enables you to automatically resolve messages using the client's locale. This is done with LocaleResolver objects. When a request comes in, the DispatcherServlet looks for a locale resolver, and if it finds one it tries to use it to set the locale. Using the RequestContext.getLocale() method, you can always retrieve the locale that was resolved by the locale resolver. In addition to automatic locale resolution, you can also attach an interceptor to the handler mapping (see for more information on handler mapping interceptors) to change the locale under specific circumstances, for example, based on a parameter in the request. Locale resolvers and interceptors are defined in the org.springframework.web.servlet.i18n package and are configured in your application context in the normal way. Here is a selection of the locale resolvers included in Spring.

This locale resolver inspects the accept-language header in the request that was sent by the client (e.g., a web browser). Usually this header field contains the locale of the client's operating system.

This locale resolver inspects a Cookie that might exist on the client to see if a locale is specified. If so, it uses the specified locale. Using the properties of this locale resolver, you can specify the name of the cookie as well as the maximum age. Find below an example of defining a CookieLocaleResolver. <bean id="localeResolver" class="org.springframework.web.servlet.i18n.CookieLocaleResolver"> <property name="cookieName" value="clientlanguage"/> <!-- in seconds. If set to -1, the cookie is not persisted (deleted when browser shuts down) --> <property name="cookieMaxAge" value="100000"> </bean> Property Default Description cookieName classname + LOCALE The name of the cookie cookieMaxAge Integer.MAX_INT The maximum time a cookie will stay persistent on the client. If -1 is specified, the cookie will not be persisted; it will only be available until the client shuts down his or her browser. cookiePath / Limits the visibility of the cookie to a certain part of your site. When cookiePath is specified, the cookie will only be visible to that path and the paths below it.

The SessionLocaleResolver allows you to retrieve locales from the session that might be associated with the user's request.

You can enable changing of locales by adding the LocaleChangeInterceptor to one of the handler mappings (see ). It will detect a parameter in the request and change the locale. It calls setLocale() on the LocaleResolver that also exists in the context. The following example shows that calls to all *.view resources containing a parameter named siteLanguage will now change the locale. So, for example, a request for the following URL, http://www.sf.net/home.view?siteLanguage=nl will change the site language to Dutch. <bean id="localeChangeInterceptor" class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor"> <property name="paramName" value="siteLanguage"/> </bean> <bean id="localeResolver" class="org.springframework.web.servlet.i18n.CookieLocaleResolver"/> <bean id="urlMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping"> <property name="interceptors"> <list> <ref bean="localeChangeInterceptor"/> </list> </property> <property name="mappings"> <value>/**/*.view=someController</value> </property> </bean>

You can apply Spring Web MVC framework themes to set the overall look-and-feel of your application, thereby enhancing user experience. A theme is a collection of static resources, typically style sheets and images, that affect the visual style of the application.

To use themes in your web application, you must set up an implementation of the org.springframework.ui.context.ThemeSource interface. The WebApplicationContext interface extends ThemeSource but delegates its responsibilities to a dedicated implementation. By default the delegate will be an org.springframework.ui.context.support.ResourceBundleThemeSource implementation that loads properties files from the root of the classpath. To use a custom ThemeSource implementation or to configure the base name prefix of the ResourceBundleThemeSource, you can register a bean in the application context with the reserved name themeSource. The web application context automatically detects a bean with that name and uses it. When using the ResourceBundleThemeSource, a theme is defined in a simple properties file. The properties file lists the resources that make up the theme. Here is an example: styleSheet=/themes/cool/style.css background=/themes/cool/img/coolBg.jpg The keys of the properties are the names that refer to the themed elements from view code. For a JSP, you typically do this using the spring:theme custom tag, which is very similar to the spring:message tag. The following JSP fragment uses the theme defined in the previous example to customize the look and feel: <%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%> <html> <head> <link rel="stylesheet" href="<spring:theme code='styleSheet'/>" type="text/css"/> </head> <body style="background=<spring:theme code='background'/>"> ... </body> </html> By default, the ResourceBundleThemeSource uses an empty base name prefix. As a result, the properties files are loaded from the root of the classpath. Thus you would put the cool.properties theme definition in a directory at the root of the classpath, for example, in /WEB-INF/classes. The ResourceBundleThemeSource uses the standard Java resource bundle loading mechanism, allowing for full internationalization of themes. For example, we could have a /WEB-INF/classes/cool_nl.properties that references a special background image with Dutch text on it.

After you define themes, as in the preceding section, you decide which theme to use. The DispatcherServlet will look for a bean named themeResolver to find out which ThemeResolver implementation to use. A theme resolver works in much the same way as a LocaleResolver. It detects the theme to use for a particular request and can also alter the request's theme. The following theme resolvers are provided by Spring: Class Description FixedThemeResolver Selects a fixed theme, set using the defaultThemeName property. SessionThemeResolver The theme is maintained in the user's HTTP session. It only needs to be set once for each session, but is not persisted between sessions. CookieThemeResolver The selected theme is stored in a cookie on the client. Spring also provides a ThemeChangeInterceptor that allows theme changes on every request with a simple request parameter.

Spring's built-in multipart support handles file uploads in web applications. You enable this multipart support with pluggable MultipartResolver objects, defined in the org.springframework.web.multipart package. Spring provides one MultipartResolver implementation for use with Commons FileUpload and another for use with Servlet 3.0 multipart request parsing. By default, Spring does no multipart handling, because some developers want to handle multiparts themselves. You enable Spring multipart handling by adding a multipart resolver to the web application's context. Each request is inspected to see if it contains a multipart. If no multipart is found, the request continues as expected. If a multipart is found in the request, the MultipartResolver that has been declared in your context is used. After that, the multipart attribute in your request is treated like any other attribute.

The following example shows how to use the CommonsMultipartResolver: <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver"> <!-- one of the properties available; the maximum file size in bytes --> <property name="maxUploadSize" value="100000"/> </bean> Of course you also need to put the appropriate jars in your classpath for the multipart resolver to work. In the case of the CommonsMultipartResolver, you need to use commons-fileupload.jar. When the Spring DispatcherServlet detects a multi-part request, it activates the resolver that has been declared in your context and hands over the request. The resolver then wraps the current HttpServletRequest into a MultipartHttpServletRequest that supports multipart file uploads. Using the MultipartHttpServletRequest, you can get information about the multiparts contained by this request and actually get access to the multipart files themselves in your controllers.

In order to use Servlet 3.0 based multipart parsing, you need to mark the DispatcherServlet with a "multipart-config" section in web.xml, or with a javax.servlet.MultipartConfigElement in programmatic Servlet registration, or in case of a custom Servlet class possibly with a javax.servlet.annotation.MultipartConfig annotation on your Servlet class. Configuration settings such as maximum sizes or storage locations need to be applied at that Servlet registration level as Servlet 3.0 does not allow for those settings to be done from the MultipartResolver. Once Servlet 3.0 multipart parsing has been enabled in one of the above mentioned ways you can add the StandardServletMultipartResolver to your Spring configuration: <bean id="multipartResolver" class="org.springframework.web.multipart.support.StandardServletMultipartResolver"> </bean>

After the MultipartResolver completes its job, the request is processed like any other. First, create a form with a file input that will allow the user to upload a form. The encoding attribute (enctype="multipart/form-data") lets the browser know how to encode the form as multipart request: <html> <head> <title>Upload a file please</title> </head> <body> <h1>Please upload a file</h1> <form method="post" action="/form" enctype="multipart/form-data"> <input type="text" name="name"/> <input type="file" name="file"/> <input type="submit"/> </form> </body> </html> The next step is to create a controller that handles the file upload. This controller is very similar to a normal annotated @Controller, except that we use MultipartHttpServletRequest or MultipartFile in the method parameters: @Controller public class FileUpoadController { @RequestMapping(value = "/form", method = RequestMethod.POST) public String handleFormUpload(@RequestParam("name") String name, @RequestParam("file") MultipartFile file) { if (!file.isEmpty()) { byte[] bytes = file.getBytes(); // store the bytes somewhere return "redirect:uploadSuccess"; } else { return "redirect:uploadFailure"; } } } Note how the @RequestParam method parameters map to the input elements declared in the form. In this example, nothing is done with the byte[], but in practice you can save it in a database, store it on the file system, and so on. When using Servlet 3.0 multipart parsing you can also use javax.servlet.http.Part for the method parameter: @Controller public class FileUpoadController { @RequestMapping(value = "/form", method = RequestMethod.POST) public String handleFormUpload(@RequestParam("name") String name, @RequestParam("file") Part file) { InputStream inputStream = file.getInputStream(); // store bytes from uploaded file somewhere return "redirect:uploadSuccess"; } }

Multipart requests can also be submitted from non-browser clients in a RESTful service scenario. All of the above examples and configuration apply here as well. However, unlike browsers that typically submit files and simple form fields, a programmatic client can also send more complex data of a specific content type — for example a multipart request with a file and second part with JSON formatted data: POST /someUrl Content-Type: multipart/mixed --edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp Content-Disposition: form-data; name="meta-data" Content-Type: application/json; charset=UTF-8 Content-Transfer-Encoding: 8bit { "name": "value" } --edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp Content-Disposition: form-data; name="file-data"; filename="file.properties" Content-Type: text/xml Content-Transfer-Encoding: 8bit ... File Data ... You could access the part named "meta-data" with a @RequestParam("meta-data") String metadata controller method argument. However, you would probably prefer to accept a strongly typed object initialized from the JSON formatted data in the body of the request part, very similar to the way @RequestBody converts the body of a non-multipart request to a target object with the help of an HttpMessageConverter. You can use the @RequestPart annotation instead of the @RequestParam annotation for this purpose. It allows you to have the content of a specific multipart passed through an HttpMessageConverter taking into consideration the 'Content-Type' header of the multipart: @RequestMapping(value="/someUrl", method = RequestMethod.POST) public String onSubmit(@RequestPart("meta-data") MetaData metadata, @RequestPart("file-data") MultipartFile file) { // ... } Notice how MultipartFile method arguments can be accessed with @RequestParam or with @RequestPart interchangeably. However, the @RequestPart("meta-data") MetaData method argument in this case is read as JSON content based on its 'Content-Type' header and converted with the help of the MappingJacksonHttpMessageConverter.

Spring HandlerExceptionResolver implementations deal with unexpected exceptions that occur during controller execution. A HandlerExceptionResolver somewhat resembles the exception mappings you can define in the web application descriptor web.xml. However, they provide a more flexible way to do so. For example they provide information about which handler was executing when the exception was thrown. Furthermore, a programmatic way of handling exceptions gives you more options for responding appropriately before the request is forwarded to another URL (the same end result as when you use the Servlet specific exception mappings). Besides implementing the HandlerExceptionResolver interface, which is only a matter of implementing the resolveException(Exception, Handler) method and returning a ModelAndView, you may also use the SimpleMappingExceptionResolver. This resolver enables you to take the class name of any exception that might be thrown and map it to a view name. This is functionally equivalent to the exception mapping feature from the Servlet API, but it is also possible to implement more finely grained mappings of exceptions from different handlers. By default, the DispatcherServlet registers the DefaultHandlerExceptionResolver. This resolver handles certain standard Spring MVC exceptions by setting a specific response status code: Exception HTTP Status Code ConversionNotSupportedException 500 (Internal Server Error) HttpMediaTypeNotAcceptableException 406 (Not Acceptable) HttpMediaTypeNotSupportedException 415 (Unsupported Media Type) HttpMessageNotReadableException 400 (Bad Request) HttpMessageNotWritableException 500 (Internal Server Error) HttpRequestMethodNotSupportedException 405 (Method Not Allowed) MissingServletRequestParameterException 400 (Bad Request) NoSuchRequestHandlingMethodException 404 (Not Found) TypeMismatchException 400 (Bad Request)

An alternative to the HandlerExceptionResolver interface is the @ExceptionHandler annotation. You use the @ExceptionHandler method annotation within a controller to specify which method is invoked when an exception of a specific type is thrown during the execution of controller methods. For example: @Controller public class SimpleController { // other controller method omitted @ExceptionHandler(IOException.class) public String handleIOException(IOException ex, HttpServletRequest request) { return ClassUtils.getShortName(ex.getClass()); } } will invoke the 'handlerIOException' method when a java.io.IOException is thrown. The @ExceptionHandler value can be set to an array of Exception types. If an exception is thrown matches one of the types in the list, then the method annotated with the matching @ExceptionHandler will be invoked. If the annotation value is not set then the exception types listed as method arguments are used. Much like standard controller methods annotated with a @RequestMapping annotation, the method arguments and return values of @ExceptionHandler methods are very flexible. For example, the HttpServletRequest can be accessed in Servlet environments and the PortletRequest in Portlet environments. The return type can be a String, which is interpreted as a view name or a ModelAndView object. Refer to the API documentation for more details.

For a lot of projects, sticking to established conventions and having reasonable defaults is just what they (the projects) need, and Spring Web MVC now has explicit support for convention over configuration. What this means is that if you establish a set of naming conventions and suchlike, you can substantially cut down on the amount of configuration that is required to set up handler mappings, view resolvers, ModelAndView instances, etc. This is a great boon with regards to rapid prototyping, and can also lend a degree of (always good-to-have) consistency across a codebase should you choose to move forward with it into production. Convention-over-configuration support addresses the three core areas of MVC: models, views, and controllers.

The ControllerClassNameHandlerMapping class is a HandlerMapping implementation that uses a convention to determine the mapping between request URLs and the Controller instances that are to handle those requests. Consider the following simple Controller implementation. Take special notice of the name of the class. public class ViewShoppingCartController implements Controller { public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) { // the implementation is not hugely important for this example... } } Here is a snippet from the corresponding Spring Web MVC configuration file: <bean class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping"/> <bean id="viewShoppingCart" class="x.y.z.ViewShoppingCartController"> <!-- inject dependencies as required... --> </bean> The ControllerClassNameHandlerMapping finds all of the various handler (or Controller) beans defined in its application context and strips Controller off the name to define its handler mappings. Thus, ViewShoppingCartController maps to the /viewshoppingcart* request URL. Let's look at some more examples so that the central idea becomes immediately familiar. (Notice all lowercase in the URLs, in contrast to camel-cased Controller class names.) WelcomeController maps to the /welcome* request URL HomeController maps to the /home* request URL IndexController maps to the /index* request URL RegisterController maps to the /register* request URL In the case of MultiActionController handler classes, the mappings generated are slightly more complex. The Controller names in the following examples are assumed to be MultiActionController implementations: AdminController maps to the /admin/* request URL CatalogController maps to the /catalog/* request URL If you follow the convention of naming your Controller implementations as xxxController, the ControllerClassNameHandlerMapping saves you the tedium of defining and maintaining a potentially looooong SimpleUrlHandlerMapping (or suchlike). The ControllerClassNameHandlerMapping class extends the AbstractHandlerMapping base class so you can define HandlerInterceptor instances and everything else just as you would with many other HandlerMapping implementations.

The ModelMap class is essentially a glorified Map that can make adding objects that are to be displayed in (or on) a View adhere to a common naming convention. Consider the following Controller implementation; notice that objects are added to the ModelAndView without any associated name specified. public class DisplayShoppingCartController implements Controller { public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) { List cartItems = // get a List of CartItem objects User user = // get the User doing the shopping ModelAndView mav = new ModelAndView("displayShoppingCart"); <-- the logical view name mav.addObject(cartItems); <-- look ma, no name, just the object mav.addObject(user); <-- and again ma! return mav; } } The ModelAndView class uses a ModelMap class that is a custom Map implementation that automatically generates a key for an object when an object is added to it. The strategy for determining the name for an added object is, in the case of a scalar object such as User, to use the short class name of the object's class. The following examples are names that are generated for scalar objects put into a ModelMap instance. An x.y.User instance added will have the name user generated. An x.y.Registration instance added will have the name registration generated. An x.y.Foo instance added will have the name foo generated. A java.util.HashMap instance added will have the name hashMap generated. You probably want to be explicit about the name in this case because hashMap is less than intuitive. Adding null will result in an IllegalArgumentException being thrown. If the object (or objects) that you are adding could be null, then you will also want to be explicit about the name. Spring Web MVC's convention-over-configuration support does not support automatic pluralization. That is, you cannot add a List of Person objects to a ModelAndView and have the generated name be people. This decision was made after some debate, with the Principle of Least Surprise winning out in the end. The strategy for generating a name after adding a Set or a List is to peek into the collection, take the short class name of the first object in the collection, and use that with List appended to the name. The same applies to arrays although with arrays it is not necessary to peek into the array contents. A few examples will make the semantics of name generation for collections clearer: An x.y.User[] array with zero or more x.y.User elements added will have the name userList generated. An x.y.Foo[] array with zero or more x.y.User elements added will have the name fooList generated. A java.util.ArrayList with one or more x.y.User elements added will have the name userList generated. A java.util.HashSet with one or more x.y.Foo elements added will have the name fooList generated. An empty java.util.ArrayList will not be added at all (in effect, the addObject(..) call will essentially be a no-op).

The RequestToViewNameTranslator interface determines a logical View name when no such logical view name is explicitly supplied. It has just one implementation, the DefaultRequestToViewNameTranslator class. The DefaultRequestToViewNameTranslator maps request URLs to logical view names, as with this example: public class RegistrationController implements Controller { public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) { // process the request... ModelAndView mav = new ModelAndView(); // add data as necessary to the model... return mav; // notice that no View or logical view name has been set } } <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> <!-- this bean with the well known name generates view names for us --> <bean id="viewNameTranslator" class="org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator"/> <bean class="x.y.RegistrationController"> <!-- inject dependencies as necessary --> </bean> <!-- maps request URLs to Controller names --> <bean class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping"/> <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> </bean> </beans> Notice how in the implementation of the handleRequest(..) method no View or logical view name is ever set on the ModelAndView that is returned. The DefaultRequestToViewNameTranslator is tasked with generating a logical view name from the URL of the request. In the case of the above RegistrationController, which is used in conjunction with the ControllerClassNameHandlerMapping, a request URL of http://localhost/registration.html results in a logical view name of registration being generated by the DefaultRequestToViewNameTranslator. This logical view name is then resolved into the /WEB-INF/jsp/registration.jsp view by the InternalResourceViewResolver bean. You do not need to define a DefaultRequestToViewNameTranslator bean explicitly. If you like the default settings of the DefaultRequestToViewNameTranslator, you can rely on the Spring Web MVC DispatcherServlet to instantiate an instance of this class if one is not explicitly configured. Of course, if you need to change the default settings, then you do need to configure your own DefaultRequestToViewNameTranslator bean explicitly. Consult the comprehensive Javadoc for the DefaultRequestToViewNameTranslator class for details of the various properties that can be configured.

An ETag (entity tag) is an HTTP response header returned by an HTTP/1.1 compliant web server used to determine change in content at a given URL. It can be considered to be the more sophisticated successor to the Last-Modified header. When a server returns a representation with an ETag header, the client can use this header in subsequent GETs, in an If-None-Match header. If the content has not changed, the server returns 304: Not Modified. Support for ETags is provided by the Servlet filter ShallowEtagHeaderFilter. It is a plain Servlet Filter, and thus can be used in combination with any web framework. The ShallowEtagHeaderFilter filter creates so-called shallow ETags (as opposed to deep ETags, more about that later).The filter caches the content of the rendered JSP (or other content), generates an MD5 hash over that, and returns that as an ETag header in the response. The next time a client sends a request for the same resource, it uses that hash as the If-None-Match value. The filter detects this, renders the view again, and compares the two hashes. If they are equal, a 304 is returned. This filter will not save processing power, as the view is still rendered. The only thing it saves is bandwidth, as the rendered response is not sent back over the wire. You configure the ShallowEtagHeaderFilter in web.xml: <filter> <filter-name>etagFilter</filter-name> <filter-class>org.springframework.web.filter.ShallowEtagHeaderFilter</filter-class> </filter> <filter-mapping> <filter-name>etagFilter</filter-name> <servlet-name>petclinic</servlet-name> </filter-mapping>

Spring 3 introduces a mvc XML configuration namespace that simplifies the setup of Spring MVC inside your web application. Instead of registering low-level beans such as AnnotationMethodHandlerAdapter, you can simply use the namespace and its higher-level constructs. This is generally preferred unless you require finer-grained control of the configuration at the bean level. The mvc namespace consists of three tags: mvc:annotation-driven, mvc:interceptors, and mvc:view-controller. Each of these tags is documented below and in the XML schema.

This tag registers the RequestMappingHandlerMapping and RequestMappingHandlerAdapter beans that are required for Spring MVC to dispatch requests to @Controllers. The tag configures those two beans with sensible defaults based on what is present in your classpath. The defaults are: Support for Spring 3's Type ConversionService in addition to JavaBeans PropertyEditors during Data Binding. A ConversionService instance produced by the org.springframework.format.support.FormattingConversionServiceFactoryBean is used by default. This can be overridden by setting the conversion-service attribute. Support for formatting Number fields using the @NumberFormat annotation Support for formatting Date, Calendar, Long, and Joda Time fields using the @DateTimeFormat annotation, if Joda Time 1.3 or higher is present on the classpath. Support for validating @Controller inputs with @Valid, if a JSR-303 Provider is present on the classpath. The validation system can be explicitly configured by setting the validator attribute. HttpMessageConverter support for @RequestBody method parameters and @ResponseBody method return values. This is the complete list of HttpMessageConverters set up by mvc:annotation-driven: ByteArrayHttpMessageConverter converts byte arrays. StringHttpMessageConverter converts strings. ResourceHttpMessageConverter converts to/from org.springframework.core.io.Resource for all media types. SourceHttpMessageConverter converts to/from a javax.xml.transform.Source. FormHttpMessageConverter converts form data to/from a MultiValueMap<String, String>. Jaxb2RootElementHttpMessageConverter converts Java objects to/from XML — added if JAXB2 is present on the classpath. MappingJacksonHttpMessageConverter converts to/from JSON — added if Jackson is present on the classpath. AtomFeedHttpMessageConverter converts Atom feeds — added if Rome is present on the classpath. RssChannelHttpMessageConverter converts RSS feeds — added if Rome is present on the classpath. You can provide your own HttpMessageConverters through the mvc:message-converters sub-element of mvc:annotation-driven. Message converters you provide will take precedence over the ones registered by default. A typical usage is shown below: <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd"> <!-- JSR-303 support will be detected on classpath and enabled automatically --> <mvc:annotation-driven/> </beans>

This tag allows you to register custom HandlerInterceptors or WebRequestInterceptors that should be applied to all HandlerMapping beans. You can also restrict the URL paths that specific interceptors apply to. An example of registering an interceptor applied to all URL paths: <mvc:interceptors> <bean class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor" /> </mvc:interceptors> An example of registering an interceptor limited to a specific URL path: <mvc:interceptors> <mvc:interceptor> <mapping path="/secure/*"/> <bean class="org.example.SecurityInterceptor" /> </mvc:interceptor> </mvc:interceptors>

This tag is a shortcut for defining a ParameterizableViewController that immediately forwards to a view when invoked. Use it in static cases when there is no Java Controller logic to execute before the view generates the response. An example of view-controller that forwards to a home page is shown below: <mvc:view-controller path="/" view-name="home"/>

This tag allows static resource requests following a particular URL pattern to be served by a ResourceHttpRequestHandler from any of a list of Resource locations. This provides a convenient way to serve static resources from locations other than the web application root, including locations on the classpath. The cache-period property may be used to set far future expiration headers (1 year is the recommendation of optimization tools such as Page Speed and YSlow) so that they will be more efficiently utilized by the client. The handler also properly evaluates the Last-Modified header (if present) so that a 304 status code will be returned as appropriate, avoiding unnecessary overhead for resources that are already cached by the client. For example, to serve resource requests with a URL pattern of /resources/** from a public-resources directory within the web application root, the tag would be used as follows: <mvc:resources mapping="/resources/**" location="/public-resources/"/> To serve these resources with a 1-year future expiration to ensure maximum use of the browser cache and a reduction in HTTP requests made by the browser: <mvc:resources mapping="/resources/**" location="/public-resources/" cache-period="31556926"/> The mapping attribute must be an Ant pattern that can be used by SimpleUrlHandlerMapping, and the location attribute must specify one or more valid resource directory locations. Multiple resource locations may be specified using a comma-separated list of values. The locations specified will be checked in the specified order for the presence of the resource for any given request. For example, to enable the serving of resources from both the web application root and from a known path of /META-INF/public-web-resources/ in any jar on the classpath, the tag would be specified as: <mvc:resources mapping="/resources/**" location="/, classpath:/META-INF/public-web-resources/"/> When serving resources that may change when a new version of the application is deployed, it is recommended that you incorporate a version string into the mapping pattern used to request the resources, so that you may force clients to request the newly deployed version of your application's resources. Such a version string can be parameterized and accessed using SpEL so that it may be easily managed in a single place when deploying new versions. As an example, let's consider an application that uses a performance-optimized custom build (as recommended) of the Dojo JavaScript library in production, and that the build is generally deployed within the web application at a path of /public-resources/dojo/dojo.js. Since different parts of Dojo may be incorporated into the custom build for each new version of the application, the client web browsers need to be forced to re-download that custom-built dojo.js resource any time a new version of the application is deployed. A simple way to achieve this would be to manage the version of the application in a properties file, such as: application.version=1.0.0 and then to make the properties file's values accessible to SpEL as a bean using the util:properties tag: <util:properties id="applicationProps" location="/WEB-INF/spring/application.properties"/> With the application version now accessible via SpEL, we can incorporate this into the use of the resources tag: <mvc:resources mapping="/resources-#{applicationProps['application.version']}/**" location="/public-resources/"/> and finally, to request the resource with the proper URL, we can take advantage of the Spring JSP tags: <spring:eval expression="@applicationProps['application.version']" var="applicationVersion"/> <spring:url value="/resources-{applicationVersion}" var="resourceUrl"> <spring:param name="applicationVersion" value="${applicationVersion}"/> </spring:url> <script src="${resourceUrl}/dojo/dojo.js" type="text/javascript"> </script>

This tag allows for mapping the DispatcherServlet to "/" (thus overriding the mapping of the container's default Servlet), while still allowing static resource requests to be handled by the container's default Servlet. It configures a DefaultServletHttpRequestHandler with a URL mapping of "/**" and the lowest priority relative to other URL mappings. This handler will forward all requests to the default Servlet. Therefore it is important that it remains last in the order of all other URL HandlerMappings. That will be the case if you use <mvc:annotation-driven> or alternatively if you are setting up your own customized HandlerMapping instance be sure to set its order property to a value lower than that of the DefaultServletHttpRequestHandler, which is Integer.MAX_VALUE. To enable the feature using the default setup, simply include the tag in the form: <mvc:default-servlet-handler/> The caveat to overriding the "/" Servlet mapping is that the RequestDispatcher for the default Servlet must be retrieved by name rather than by path. The DefaultServletHttpRequestHandler will attempt to auto-detect the default Servlet for the container at startup time, using a list of known names for most of the major Servlet containers (including Tomcat, Jetty, Glassfish, JBoss, Resin, WebLogic, and WebSphere). If the default Servlet has been custom configured with a different name, or if a different Servlet container is being used where the default Servlet name is unknown, then the default Servlet's name must be explicitly provided as in the following example: <mvc:default-servlet-handler default-servlet-name="myCustomDefaultServlet"/>

See the following links and pointers for more resources about Spring Web MVC: There are many excellent articles and tutorials that show how to build web applications with Spring MVC. Read them at the Spring Documentation page. Expert Spring Web MVC and Web Flow by Seth Ladd and others (published by Apress) is an excellent hard copy source of Spring Web MVC goodness.