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Common classes used in different Spring Cloud implementations
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<html><head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Cloud Native Applications</title><link rel="stylesheet" type="text/css" href="css/manual-singlepage.css"><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div lang="en" class="book"><div class="titlepage"><div><div><h1 class="title"><a name="d0e3"></a>Cloud Native Applications</h1></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="preface"><a href="#d0e9"></a></span></dt><dt><span class="chapter"><a href="#_spring_cloud_context_application_context_services">1. Spring Cloud Context: Application Context Services</a></span></dt><dd><dl><dt><span class="section"><a href="#_the_bootstrap_application_context">1.1. The Bootstrap Application Context</a></span></dt><dt><span class="section"><a href="#_application_context_hierarchies">1.2. Application Context Hierarchies</a></span></dt><dt><span class="section"><a href="#customizing-bootstrap-properties">1.3. Changing the Location of Bootstrap Properties</a></span></dt><dt><span class="section"><a href="#overriding-bootstrap-properties">1.4. Overriding the Values of Remote Properties</a></span></dt><dt><span class="section"><a href="#_customizing_the_bootstrap_configuration">1.5. Customizing the Bootstrap Configuration</a></span></dt><dt><span class="section"><a href="#customizing-bootstrap-property-sources">1.6. Customizing the Bootstrap Property Sources</a></span></dt><dt><span class="section"><a href="#_environment_changes">1.7. Environment Changes</a></span></dt><dt><span class="section"><a href="#_refresh_scope">1.8. Refresh Scope</a></span></dt><dt><span class="section"><a href="#_encryption_and_decryption">1.9. Encryption and Decryption</a></span></dt><dt><span class="section"><a href="#_endpoints">1.10. Endpoints</a></span></dt></dl></dd><dt><span class="chapter"><a href="#_spring_cloud_commons_common_abstractions">2. Spring Cloud Commons: Common Abstractions</a></span></dt><dd><dl><dt><span class="section"><a href="#__enablediscoveryclient">2.1. @EnableDiscoveryClient</a></span></dt><dd><dl><dt><span class="section"><a href="#_health_indicator">2.1.1. Health Indicator</a></span></dt></dl></dd><dt><span class="section"><a href="#_serviceregistry">2.2. ServiceRegistry</a></span></dt><dd><dl><dt><span class="section"><a href="#_serviceregistry_auto_registration">2.2.1. ServiceRegistry Auto-Registration</a></span></dt><dt><span class="section"><a href="#_service_registry_actuator_endpoint">2.2.2. Service Registry Actuator Endpoint</a></span></dt></dl></dd><dt><span class="section"><a href="#_spring_resttemplate_as_a_load_balancer_client">2.3. Spring RestTemplate as a Load Balancer Client</a></span></dt><dt><span class="section"><a href="#_spring_webclient_as_a_load_balancer_client">2.4. Spring WebClient as a Load Balancer Client</a></span></dt><dd><dl><dt><span class="section"><a href="#_retrying_failed_requests">2.4.1. Retrying Failed Requests</a></span></dt></dl></dd><dt><span class="section"><a href="#_multiple_resttemplate_objects">2.5. Multiple RestTemplate objects</a></span></dt><dt><span class="section"><a href="#loadbalanced-webclient">2.6. Spring WebFlux WebClient as a Load Balancer Client</a></span></dt><dt><span class="section"><a href="#ignore-network-interfaces">2.7. Ignore Network Interfaces</a></span></dt><dt><span class="section"><a href="#http-clients">2.8. HTTP Client Factories</a></span></dt><dt><span class="section"><a href="#enabled-features">2.9. Enabled Features</a></span></dt><dd><dl><dt><span class="section"><a href="#_feature_types">2.9.1. Feature types</a></span></dt><dt><span class="section"><a href="#_declaring_features">2.9.2. Declaring features</a></span></dt></dl></dd></dl></dd></dl></div><div class="preface"><div class="titlepage"><div><div><h1 class="title"><a name="d0e9" href="#d0e9"></a></h1></div></div></div><p><a class="link" href="http://pivotal.io/platform-as-a-service/migrating-to-cloud-native-application-architectures-ebook" target="_top">Cloud Native</a> is a style of application development that encourages easy adoption of best practices in the areas of continuous delivery and value-driven development.
A related discipline is that of building <a class="link" href="http://12factor.net/" target="_top">12-factor Applications</a>, in which development practices are aligned with delivery and operations goals&#8201;&#8212;&#8201;for instance, by using declarative programming and management and monitoring.
Spring Cloud facilitates these styles of development in a number of specific ways.
The starting point is a set of features to which all components in a distributed system need easy access.</p><p>Many of those features are covered by <a class="link" href="http://projects.spring.io/spring-boot" target="_top">Spring Boot</a>, on which Spring Cloud builds. Some more features are delivered by Spring Cloud as two libraries: Spring Cloud Context and Spring Cloud Commons.
Spring Cloud Context provides utilities and special services for the <code class="literal">ApplicationContext</code> of a Spring Cloud application (bootstrap context, encryption, refresh scope, and environment endpoints). Spring Cloud Commons is a set of abstractions and common classes used in different Spring Cloud implementations (such as Spring Cloud Netflix and Spring Cloud Consul).</p><p>If you get an exception due to "Illegal key size" and you use Sun&#8217;s JDK, you need to install the Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files.
See the following links for more information:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><a class="link" href="http://www.oracle.com/technetwork/java/javase/downloads/jce-6-download-429243.html" target="_top">Java 6 JCE</a></li><li class="listitem"><a class="link" href="http://www.oracle.com/technetwork/java/javase/downloads/jce-7-download-432124.html" target="_top">Java 7 JCE</a></li><li class="listitem"><a class="link" href="http://www.oracle.com/technetwork/java/javase/downloads/jce8-download-2133166.html" target="_top">Java 8 JCE</a></li></ul></div><p>Extract the files into the JDK/jre/lib/security folder for whichever version of JRE/JDK x64/x86 you use.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>Spring Cloud is released under the non-restrictive Apache 2.0 license.
If you would like to contribute to this section of the documentation or if you find an error, you can find the source code and issue trackers for the project at <a class="link" href="https://github.com/spring-cloud/spring-cloud-commons/tree/master/docs/src/main/asciidoc" target="_top">github</a>.</p></td></tr></table></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="_spring_cloud_context_application_context_services" href="#_spring_cloud_context_application_context_services"></a>1.&nbsp;Spring Cloud Context: Application Context Services</h1></div></div></div><p>Spring Boot has an opinionated view of how to build an application with Spring.
For instance, it has conventional locations for common configuration files and has endpoints for common management and monitoring tasks.
Spring Cloud builds on top of that and adds a few features that probably all components in a system would use or occasionally need.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_the_bootstrap_application_context" href="#_the_bootstrap_application_context"></a>1.1&nbsp;The Bootstrap Application Context</h2></div></div></div><p>A Spring Cloud application operates by creating a &#8220;bootstrap&#8221; context, which is a parent context for the main application.
It is responsible for loading configuration properties from the external sources and for decrypting properties in the local external configuration files.
The two contexts share an <code class="literal">Environment</code>, which is the source of external properties for any Spring application.
By default, bootstrap properties are added with high precedence, so they cannot be overridden by local configuration.</p><p>The bootstrap context uses a different convention for locating external configuration than the main application context.
Instead of <code class="literal">application.yml</code> (or <code class="literal">.properties</code>), you can use <code class="literal">bootstrap.yml</code>, keeping the external configuration for bootstrap and main context
nicely separate.
The following listing shows an example:</p><p><b>bootstrap.yml.&nbsp;</b>
</p><pre class="screen">spring:
application:
name: foo
cloud:
config:
uri: ${SPRING_CONFIG_URI:http://localhost:8888}</pre><p>
</p><p>If your application needs any application-specific configuration from the server, it is a good idea to set the <code class="literal">spring.application.name</code> (in <code class="literal">bootstrap.yml</code> or <code class="literal">application.yml</code>).</p><p>You can disable the bootstrap process completely by setting <code class="literal">spring.cloud.bootstrap.enabled=false</code> (for example, in system properties).</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_application_context_hierarchies" href="#_application_context_hierarchies"></a>1.2&nbsp;Application Context Hierarchies</h2></div></div></div><p>If you build an application context from <code class="literal">SpringApplication</code> or <code class="literal">SpringApplicationBuilder</code>, then the Bootstrap context is added as a parent to that context.
It is a feature of Spring that child contexts inherit property sources and profiles from their parent, so the &#8220;main&#8221; application context contains additional property sources, compared to building the same context without Spring Cloud Config.
The additional property sources are:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">&#8220;bootstrap&#8221;: If any <code class="literal">PropertySourceLocators</code> are found in the Bootstrap context and if they have non-empty properties, an optional <code class="literal">CompositePropertySource</code> appears with high priority.
An example would be properties from the Spring Cloud Config Server.
See &#8220;<a class="xref" href="#customizing-bootstrap-property-sources" title="1.6&nbsp;Customizing the Bootstrap Property Sources">Section&nbsp;1.6, &#8220;Customizing the Bootstrap Property Sources&#8221;</a>&#8221; for instructions on how to customize the contents of this property source.</li><li class="listitem">&#8220;applicationConfig: [classpath:bootstrap.yml]&#8221; (and related files if Spring profiles are active): If you have a <code class="literal">bootstrap.yml</code> (or <code class="literal">.properties</code>), those properties are used to configure the Bootstrap context.
Then they get added to the child context when its parent is set.
They have lower precedence than the <code class="literal">application.yml</code> (or <code class="literal">.properties</code>) and any other property sources that are added to the child as a normal part of the process of creating a Spring Boot application.
See &#8220;<a class="xref" href="#customizing-bootstrap-properties" title="1.3&nbsp;Changing the Location of Bootstrap Properties">Section&nbsp;1.3, &#8220;Changing the Location of Bootstrap Properties&#8221;</a>&#8221; for instructions on how to customize the contents of these property sources.</li></ul></div><p>Because of the ordering rules of property sources, the &#8220;bootstrap&#8221; entries take precedence.
However, note that these do not contain any data from <code class="literal">bootstrap.yml</code>, which has very low precedence but can be used to set defaults.</p><p>You can extend the context hierarchy by setting the parent context of any <code class="literal">ApplicationContext</code> you create&#8201;&#8212;&#8201;for example, by using its own interface or with the <code class="literal">SpringApplicationBuilder</code> convenience methods (<code class="literal">parent()</code>, <code class="literal">child()</code> and <code class="literal">sibling()</code>).
The bootstrap context is the parent of the most senior ancestor that you create yourself.
Every context in the hierarchy has its own &#8220;bootstrap&#8221; (possibly empty) property source to avoid promoting values inadvertently from parents down to their descendants.
If there is a Config Server, every context in the hierarchy can also (in principle) have a different <code class="literal">spring.application.name</code> and, hence, a different remote property source.
Normal Spring application context behavior rules apply to property resolution: properties from a child context override those in
the parent, by name and also by property source name.
(If the child has a property source with the same name as the parent, the value from the parent is not included in the child).</p><p>Note that the <code class="literal">SpringApplicationBuilder</code> lets you share an <code class="literal">Environment</code> amongst the whole hierarchy, but that is not the default.
Thus, sibling contexts, in particular, do not need to have the same profiles or property sources, even though they may share common values with their parent.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="customizing-bootstrap-properties" href="#customizing-bootstrap-properties"></a>1.3&nbsp;Changing the Location of Bootstrap Properties</h2></div></div></div><p>The <code class="literal">bootstrap.yml</code> (or <code class="literal">.properties</code>) location can be specified by setting <code class="literal">spring.cloud.bootstrap.name</code> (default: <code class="literal">bootstrap</code>) or <code class="literal">spring.cloud.bootstrap.location</code> (default: empty)&#8201;&#8212;&#8201;for example, in System properties.
Those properties behave like the <code class="literal">spring.config.*</code> variants with the same name.
In fact, they are used to set up the bootstrap <code class="literal">ApplicationContext</code> by setting those properties in its <code class="literal">Environment</code>.
If there is an active profile (from <code class="literal">spring.profiles.active</code> or through the <code class="literal">Environment</code> API in the
context you are building), properties in that profile get loaded as well, the same as in a regular Spring Boot app&#8201;&#8212;&#8201;for example, from <code class="literal">bootstrap-development.properties</code> for a <code class="literal">development</code> profile.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="overriding-bootstrap-properties" href="#overriding-bootstrap-properties"></a>1.4&nbsp;Overriding the Values of Remote Properties</h2></div></div></div><p>The property sources that are added to your application by the bootstrap context are often &#8220;remote&#8221; (from example, from Spring Cloud Config Server).
By default, they cannot be overridden locally, except on the command line.
If you want to let your applications override the remote properties with their own System properties or config files, the remote property source has to grant it permission by setting <code class="literal">spring.cloud.config.allowOverride=true</code> (it does not work to set this locally).
Once that flag is set, two finer-grained settings control the location of the remote properties in relation to system properties and the application&#8217;s local configuration:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><code class="literal">spring.cloud.config.overrideNone=true</code>: Override from any local property source.</li><li class="listitem"><code class="literal">spring.cloud.config.overrideSystemProperties=false</code>: Only system properties and environment variables (but not the local config files) should override the remote settings.</li></ul></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_customizing_the_bootstrap_configuration" href="#_customizing_the_bootstrap_configuration"></a>1.5&nbsp;Customizing the Bootstrap Configuration</h2></div></div></div><p>The bootstrap context can be set to do anything you like by adding entries to <code class="literal">/META-INF/spring.factories</code> under a key named <code class="literal">org.springframework.cloud.bootstrap.BootstrapConfiguration</code>.
This holds a comma-separated list of Spring <code class="literal">@Configuration</code> classes that are used to create the context.
Any beans that you want to be available to the main application context for autowiring can be created here.
There is a special contract for <code class="literal">@Beans</code> of type <code class="literal">ApplicationContextInitializer</code>.
If you want to control the startup sequence, classes can be marked with an <code class="literal">@Order</code> annotation (the default order is <code class="literal">last</code>).</p><div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Warning"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="images/warning.png"></td><th align="left">Warning</th></tr><tr><td align="left" valign="top"><p>When adding custom <code class="literal">BootstrapConfiguration</code>, be careful that the classes you add are not <code class="literal">@ComponentScanned</code> by mistake into your &#8220;main&#8221; application context, where they might not be needed.
Use a separate package name for boot configuration classes and make sure that name is not already covered by your <code class="literal">@ComponentScan</code> or <code class="literal">@SpringBootApplication</code> annotated configuration classes.</p></td></tr></table></div><p>The bootstrap process ends by injecting initializers into the main <code class="literal">SpringApplication</code> instance (which is the normal Spring Boot startup sequence, whether it is running as a standalone application or deployed in an application server).
First, a bootstrap context is created from the classes found in <code class="literal">spring.factories</code>.
Then, all <code class="literal">@Beans</code> of type <code class="literal">ApplicationContextInitializer</code> are added to the main <code class="literal">SpringApplication</code> before it is started.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="customizing-bootstrap-property-sources" href="#customizing-bootstrap-property-sources"></a>1.6&nbsp;Customizing the Bootstrap Property Sources</h2></div></div></div><p>The default property source for external configuration added by the bootstrap process is the Spring Cloud Config Server, but you can add additional sources by adding beans of type <code class="literal">PropertySourceLocator</code> to the bootstrap context (through <code class="literal">spring.factories</code>).
For instance, you can insert additional properties from a different server or from a database.</p><p>As an example, consider the following custom locator:</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@Configuration</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> CustomPropertySourceLocator <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">implements</span> PropertySourceLocator {
<em><span class="hl-annotation" style="color: gray">@Override</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> PropertySource&lt;?&gt; locate(Environment environment) {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> MapPropertySource(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"customProperty"</span>,
Collections.&lt;String, Object&gt;singletonMap(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"property.from.sample.custom.source"</span>, <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"worked as intended"</span>));
}
}</pre><p>The <code class="literal">Environment</code> that is passed in is the one for the <code class="literal">ApplicationContext</code> about to be created&#8201;&#8212;&#8201;in other words, the one for which we supply additional property sources for.
It already has its normal Spring Boot-provided property sources, so you can use those to locate a property source specific to this <code class="literal">Environment</code> (for example, by keying it on <code class="literal">spring.application.name</code>, as is done in the default Spring Cloud Config Server property source locator).</p><p>If you create a jar with this class in it and then add a <code class="literal">META-INF/spring.factories</code> containing the following, the <code class="literal">customProperty</code> <code class="literal">PropertySource</code> appears in any application that includes that jar on its classpath:</p><pre class="screen">org.springframework.cloud.bootstrap.BootstrapConfiguration=sample.custom.CustomPropertySourceLocator</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_environment_changes" href="#_environment_changes"></a>1.7&nbsp;Environment Changes</h2></div></div></div><p>The application listens for an <code class="literal">EnvironmentChangeEvent</code> and reacts to the change in a couple of standard ways (additional <code class="literal">ApplicationListeners</code> can be added as <code class="literal">@Beans</code> by the user in the normal way).
When an <code class="literal">EnvironmentChangeEvent</code> is observed, it has a list of key values that have changed, and the application uses those to:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">Re-bind any <code class="literal">@ConfigurationProperties</code> beans in the context</li><li class="listitem">Set the logger levels for any properties in <code class="literal">logging.level.*</code></li></ul></div><p>Note that the Config Client does not, by default, poll for changes in the <code class="literal">Environment</code>.
Generally, we would not recommend that approach for detecting changes (although you could set it up with a
<code class="literal">@Scheduled</code> annotation).
If you have a scaled-out client application, it is better to broadcast the <code class="literal">EnvironmentChangeEvent</code> to all the instances instead of having them polling for changes (for example, by using the <a class="link" href="https://github.com/spring-cloud/spring-cloud-bus" target="_top">Spring Cloud Bus</a>).</p><p>The <code class="literal">EnvironmentChangeEvent</code> covers a large class of refresh use cases, as long as you can actually make a change to the <code class="literal">Environment</code> and publish the event.
Note that those APIs are public and part of core Spring).
You can verify that the changes are bound to <code class="literal">@ConfigurationProperties</code> beans by visiting the <code class="literal">/configprops</code> endpoint (a normal Spring Boot Actuator feature).
For instance, a <code class="literal">DataSource</code> can have its <code class="literal">maxPoolSize</code> changed at runtime (the default <code class="literal">DataSource</code> created by Spring Boot is an <code class="literal">@ConfigurationProperties</code> bean) and grow capacity dynamically.
Re-binding <code class="literal">@ConfigurationProperties</code> does not cover another large class of use cases, where you need more control over the refresh and where you need a change to be atomic over the whole <code class="literal">ApplicationContext</code>.
To address those concerns, we have <code class="literal">@RefreshScope</code>.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_refresh_scope" href="#_refresh_scope"></a>1.8&nbsp;Refresh Scope</h2></div></div></div><p>When there is a configuration change, a Spring <code class="literal">@Bean</code> that is marked as <code class="literal">@RefreshScope</code> gets special treatment.
This feature addresses the problem of stateful beans that only get their configuration injected when they are initialized.
For instance, if a <code class="literal">DataSource</code> has open connections when the database URL is changed via the <code class="literal">Environment</code>, you probably want the holders of those connections to be able to complete what they are doing.
Then, the next time something borrows a connection from the pool, it gets one with the new URL.</p><p>Refresh scope beans are lazy proxies that initialize when they are used (that is, when a method is called), and the scope acts as a cache of initialized values.
To force a bean to re-initialize on the next method call, you must invalidate its cache entry.</p><p>The <code class="literal">RefreshScope</code> is a bean in the context and has a public <code class="literal">refreshAll()</code> method to refresh all beans in the scope by clearing the target cache.
The <code class="literal">/refresh</code> endpoint exposes this functionality (over HTTP or JMX).
To refresh an individual bean by name, there is also a <code class="literal">refresh(String)</code> method.</p><p>To expose the <code class="literal">/refresh</code> endpoint, you need to add following configuration to your application:</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute">management</span>:
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> endpoints</span>:
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> web</span>:
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> exposure</span>:
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-attribute"> include</span>: refresh</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p><code class="literal">@RefreshScope</code> works (technically) on an <code class="literal">@Configuration</code> class, but it might lead to surprising behavior.
For example, it does not mean that all the <code class="literal">@Beans</code> defined in that class are themselves in <code class="literal">@RefreshScope</code>.
Specifically, anything that depends on those beans cannot rely on them being updated when a refresh is initiated, unless it is itself in <code class="literal">@RefreshScope</code>.
In that case, it is rebuilt on a refresh and its dependencies are re-injected. At that point, they are re-initialized from the refreshed <code class="literal">@Configuration</code>).</p></td></tr></table></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_encryption_and_decryption" href="#_encryption_and_decryption"></a>1.9&nbsp;Encryption and Decryption</h2></div></div></div><p>Spring Cloud has an <code class="literal">Environment</code> pre-processor for decrypting property values locally.
It follows the same rules as the Config Server and has the same external configuration through <code class="literal">encrypt.*</code>.
Thus, you can use encrypted values in the form of <code class="literal">{cipher}*</code> and, as long as there is a valid key, they are decrypted before the main application context gets the <code class="literal">Environment</code> settings.
To use the encryption features in an application, you need to include Spring Security RSA in your classpath (Maven co-ordinates: "org.springframework.security:spring-security-rsa"), and you also need the full strength JCE extensions in your JVM.</p><p>If you get an exception due to "Illegal key size" and you use Sun&#8217;s JDK, you need to install the Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files.
See the following links for more information:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><a class="link" href="http://www.oracle.com/technetwork/java/javase/downloads/jce-6-download-429243.html" target="_top">Java 6 JCE</a></li><li class="listitem"><a class="link" href="http://www.oracle.com/technetwork/java/javase/downloads/jce-7-download-432124.html" target="_top">Java 7 JCE</a></li><li class="listitem"><a class="link" href="http://www.oracle.com/technetwork/java/javase/downloads/jce8-download-2133166.html" target="_top">Java 8 JCE</a></li></ul></div><p>Extract the files into the JDK/jre/lib/security folder for whichever version of JRE/JDK x64/x86 you use.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_endpoints" href="#_endpoints"></a>1.10&nbsp;Endpoints</h2></div></div></div><p>For a Spring Boot Actuator application, some additional management endpoints are available. You can use:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><code class="literal">POST</code> to <code class="literal">/actuator/env</code> to update the <code class="literal">Environment</code> and rebind <code class="literal">@ConfigurationProperties</code> and log levels.</li><li class="listitem"><code class="literal">/actuator/refresh</code> to re-load the boot strap context and refresh the <code class="literal">@RefreshScope</code> beans.</li><li class="listitem"><code class="literal">/actuator/restart</code> to close the <code class="literal">ApplicationContext</code> and restart it (disabled by default).</li><li class="listitem"><code class="literal">/actuator/pause</code> and <code class="literal">/actuator/resume</code> for calling the <code class="literal">Lifecycle</code> methods (<code class="literal">stop()</code> and <code class="literal">start()</code> on the <code class="literal">ApplicationContext</code>).</li></ul></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="_spring_cloud_commons_common_abstractions" href="#_spring_cloud_commons_common_abstractions"></a>2.&nbsp;Spring Cloud Commons: Common Abstractions</h1></div></div></div><p>Patterns such as service discovery, load balancing, and circuit breakers lend themselves to a common abstraction layer that can be consumed by all Spring Cloud clients, independent of the implementation (for example, discovery with Eureka or Consul).</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="__enablediscoveryclient" href="#__enablediscoveryclient"></a>2.1&nbsp;@EnableDiscoveryClient</h2></div></div></div><p>Spring Cloud Commons provides the <code class="literal">@EnableDiscoveryClient</code> annotation.
This looks for implementations of the <code class="literal">DiscoveryClient</code> interface with <code class="literal">META-INF/spring.factories</code>.
Implementations of the Discovery Client add a configuration class to <code class="literal">spring.factories</code> under the <code class="literal">org.springframework.cloud.client.discovery.EnableDiscoveryClient</code> key.
Examples of <code class="literal">DiscoveryClient</code> implementations include <a class="link" href="http://cloud.spring.io/spring-cloud-netflix/" target="_top">Spring Cloud Netflix Eureka</a>, <a class="link" href="http://cloud.spring.io/spring-cloud-consul/" target="_top">Spring Cloud Consul Discovery</a>, and <a class="link" href="http://cloud.spring.io/spring-cloud-zookeeper/" target="_top">Spring Cloud Zookeeper Discovery</a>.</p><p>By default, implementations of <code class="literal">DiscoveryClient</code> auto-register the local Spring Boot server with the remote discovery server.
This behavior can be disabled by setting <code class="literal">autoRegister=false</code> in <code class="literal">@EnableDiscoveryClient</code>.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p><code class="literal">@EnableDiscoveryClient</code> is no longer required.
You can put a <code class="literal">DiscoveryClient</code> implementation on the classpath to cause the Spring Boot application to register with the service discovery server.</p></td></tr></table></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_health_indicator" href="#_health_indicator"></a>2.1.1&nbsp;Health Indicator</h3></div></div></div><p>Commons creates a Spring Boot <code class="literal">HealthIndicator</code> that <code class="literal">DiscoveryClient</code> implementations can participate in by implementing <code class="literal">DiscoveryHealthIndicator</code>.
To disable the composite <code class="literal">HealthIndicator</code>, set <code class="literal">spring.cloud.discovery.client.composite-indicator.enabled=false</code>.
A generic <code class="literal">HealthIndicator</code> based on <code class="literal">DiscoveryClient</code> is auto-configured (<code class="literal">DiscoveryClientHealthIndicator</code>).
To disable it, set <code class="literal">spring.cloud.discovery.client.health-indicator.enabled=false</code>.
To disable the description field of the <code class="literal">DiscoveryClientHealthIndicator</code>, set <code class="literal">spring.cloud.discovery.client.health-indicator.include-description=false</code>.
Otherwise, it can bubble up as the <code class="literal">description</code> of the rolled up <code class="literal">HealthIndicator</code>.</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_serviceregistry" href="#_serviceregistry"></a>2.2&nbsp;ServiceRegistry</h2></div></div></div><p>Commons now provides a <code class="literal">ServiceRegistry</code> interface that provides methods such as <code class="literal">register(Registration)</code> and <code class="literal">deregister(Registration)</code>, which let you provide custom registered services.
<code class="literal">Registration</code> is a marker interface.</p><p>The following example shows the <code class="literal">ServiceRegistry</code> in use:</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@Configuration</span></em>
<em><span class="hl-annotation" style="color: gray">@EnableDiscoveryClient(autoRegister=false)</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> MyConfiguration {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">private</span> ServiceRegistry registry;
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> MyConfiguration(ServiceRegistry registry) {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">this</span>.registry = registry;
}
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-comment">// called through some external process, such as an event or a custom actuator endpoint</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> register() {
Registration registration = constructRegistration();
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">this</span>.registry.register(registration);
}
}</pre><p>Each <code class="literal">ServiceRegistry</code> implementation has its own <code class="literal">Registry</code> implementation.</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_serviceregistry_auto_registration" href="#_serviceregistry_auto_registration"></a>2.2.1&nbsp;ServiceRegistry Auto-Registration</h3></div></div></div><p>By default, the <code class="literal">ServiceRegistry</code> implementation auto-registers the running service.
To disable that behavior, you can set:
* <code class="literal">@EnableDiscoveryClient(autoRegister=false)</code> to permanently disable auto-registration.
* <code class="literal">spring.cloud.service-registry.auto-registration.enabled=false</code> to disable the behavior through configuration.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_service_registry_actuator_endpoint" href="#_service_registry_actuator_endpoint"></a>2.2.2&nbsp;Service Registry Actuator Endpoint</h3></div></div></div><p>Spring Cloud Commons provides a <code class="literal">/service-registry</code> actuator endpoint.
This endpoint relies on a <code class="literal">Registration</code> bean in the Spring Application Context.
Calling <code class="literal">/service-registry</code> with GET returns the status of the <code class="literal">Registration</code>.
Using POST to the same endpoint with a JSON body changes the status of the current <code class="literal">Registration</code> to the new value.
The JSON body has to include the <code class="literal">status</code> field with the preferred value.
Please see the documentation of the <code class="literal">ServiceRegistry</code> implementation you use for the allowed values when updating the status and the values returned for the status.
For instance, Eureka&#8217;s supported statuses are <code class="literal">UP</code>, <code class="literal">DOWN</code>, <code class="literal">OUT_OF_SERVICE</code>, and <code class="literal">UNKNOWN</code>.</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_spring_resttemplate_as_a_load_balancer_client" href="#_spring_resttemplate_as_a_load_balancer_client"></a>2.3&nbsp;Spring RestTemplate as a Load Balancer Client</h2></div></div></div><p><code class="literal">RestTemplate</code> can be automatically configured to use ribbon.
To create a load-balanced <code class="literal">RestTemplate</code>, create a <code class="literal">RestTemplate</code> <code class="literal">@Bean</code> and use the <code class="literal">@LoadBalanced</code> qualifier, as shown in the following example:</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@Configuration</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> MyConfiguration {
<em><span class="hl-annotation" style="color: gray">@LoadBalanced</span></em>
<em><span class="hl-annotation" style="color: gray">@Bean</span></em>
RestTemplate restTemplate() {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> RestTemplate();
}
}
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> MyClass {
<em><span class="hl-annotation" style="color: gray">@Autowired</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">private</span> RestTemplate restTemplate;
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> String doOtherStuff() {
String results = restTemplate.getForObject(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"http://stores/stores"</span>, String.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>);
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> results;
}
}</pre><div class="caution" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Caution"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Caution]" src="images/caution.png"></td><th align="left">Caution</th></tr><tr><td align="left" valign="top"><p>A <code class="literal">RestTemplate</code> bean is no longer created through auto-configuration.
Individual applications must create it.</p></td></tr></table></div><p>The URI needs to use a virtual host name (that is, a service name, not a host name).
The Ribbon client is used to create a full physical address.
See <a class="link" href="https://github.com/spring-cloud/spring-cloud-netflix/blob/master/spring-cloud-netflix-core/src/main/java/org/springframework/cloud/netflix/ribbon/RibbonAutoConfiguration.java" target="_top">RibbonAutoConfiguration</a> for details of how the <code class="literal">RestTemplate</code> is set up.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_spring_webclient_as_a_load_balancer_client" href="#_spring_webclient_as_a_load_balancer_client"></a>2.4&nbsp;Spring WebClient as a Load Balancer Client</h2></div></div></div><p><code class="literal">WebClient</code> can be automatically configured to use the <code class="literal">LoadBalancerClient</code>.
To create a load-balanced <code class="literal">WebClient</code>, create a <code class="literal">WebClient.Builder</code> <code class="literal">@Bean</code> and use the <code class="literal">@LoadBalanced</code> qualifier, as shown in the following example:</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@Configuration</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> MyConfiguration {
<em><span class="hl-annotation" style="color: gray">@Bean</span></em>
<em><span class="hl-annotation" style="color: gray">@LoadBalanced</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> WebClient.Builder loadBalancedWebClientBuilder() {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> WebClient.builder();
}
}
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> MyClass {
<em><span class="hl-annotation" style="color: gray">@Autowired</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">private</span> WebClient.Builder webClientBuilder;
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> Mono&lt;String&gt; doOtherStuff() {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> webClientBuilder.build().get().uri(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"http://stores/stores"</span>)
.retrieve().bodyToMono(String.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>);
}
}</pre><p>The URI needs to use a virtual host name (that is, a service name, not a host name).
The Ribbon client is used to create a full physical address.</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_retrying_failed_requests" href="#_retrying_failed_requests"></a>2.4.1&nbsp;Retrying Failed Requests</h3></div></div></div><p>A load-balanced <code class="literal">RestTemplate</code> can be configured to retry failed requests.
By default, this logic is disabled.
You can enable it by adding <a class="link" href="https://github.com/spring-projects/spring-retry" target="_top">Spring Retry</a> to your application&#8217;s classpath.
The load-balanced <code class="literal">RestTemplate</code> honors some of the Ribbon configuration values related to retrying failed requests.
You can use <code class="literal">client.ribbon.MaxAutoRetries</code>, <code class="literal">client.ribbon.MaxAutoRetriesNextServer</code>, and <code class="literal">client.ribbon.OkToRetryOnAllOperations</code> properties.
If you would like to disable the retry logic with Spring Retry on the classpath, you can set <code class="literal">spring.cloud.loadbalancer.retry.enabled=false</code>.
See the <a class="link" href="https://github.com/Netflix/ribbon/wiki/Getting-Started#the-properties-file-sample-clientproperties" target="_top">Ribbon documentation</a> for a description of what these properties do.</p><p>If you would like to implement a <code class="literal">BackOffPolicy</code> in your retries, you need to create a bean of type <code class="literal">LoadBalancedBackOffPolicyFactory</code> and return the <code class="literal">BackOffPolicy</code> you would like to use for a given service, as shown in the following example:</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@Configuration</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> MyConfiguration {
<em><span class="hl-annotation" style="color: gray">@Bean</span></em>
LoadBalancedBackOffPolicyFactory backOffPolciyFactory() {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> LoadBalancedBackOffPolicyFactory() {
<em><span class="hl-annotation" style="color: gray">@Override</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> BackOffPolicy createBackOffPolicy(String service) {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> ExponentialBackOffPolicy();
}
};
}
}</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p><code class="literal">client</code> in the preceding examples should be replaced with your Ribbon client&#8217;s name.</p></td></tr></table></div><p>If you want to add one or more <code class="literal">RetryListener</code> implementations to your retry functionality, you need to
create a bean of type <code class="literal">LoadBalancedRetryListenerFactory</code> and return the <code class="literal">RetryListener</code> array
you would like to use for a given service, as shown in the following example:</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@Configuration</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> MyConfiguration {
<em><span class="hl-annotation" style="color: gray">@Bean</span></em>
LoadBalancedRetryListenerFactory retryListenerFactory() {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> LoadBalancedRetryListenerFactory() {
<em><span class="hl-annotation" style="color: gray">@Override</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> RetryListener[] createRetryListeners(String service) {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> RetryListener[]{<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> RetryListener() {
<em><span class="hl-annotation" style="color: gray">@Override</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> &lt;T, E <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">extends</span> Throwable&gt; <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">boolean</span> open(RetryContext context, RetryCallback&lt;T, E&gt; callback) {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-comment">//TODO Do you business...</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> true;
}
<em><span class="hl-annotation" style="color: gray">@Override</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> &lt;T, E <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">extends</span> Throwable&gt; <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> close(RetryContext context, RetryCallback&lt;T, E&gt; callback, Throwable throwable) {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-comment">//TODO Do you business...</span>
}
<em><span class="hl-annotation" style="color: gray">@Override</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> &lt;T, E <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">extends</span> Throwable&gt; <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> onError(RetryContext context, RetryCallback&lt;T, E&gt; callback, Throwable throwable) {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-comment">//TODO Do you business...</span>
}
}};
}
};
}
}</pre></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_multiple_resttemplate_objects" href="#_multiple_resttemplate_objects"></a>2.5&nbsp;Multiple RestTemplate objects</h2></div></div></div><p>If you want a <code class="literal">RestTemplate</code> that is not load-balanced, create a <code class="literal">RestTemplate</code> bean and inject it.
To access the load-balanced <code class="literal">RestTemplate</code>, use the <code class="literal">@LoadBalanced</code> qualifier when you create your <code class="literal">@Bean</code>, as shown in the following example:\</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@Configuration</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> MyConfiguration {
<em><span class="hl-annotation" style="color: gray">@LoadBalanced</span></em>
<em><span class="hl-annotation" style="color: gray">@Bean</span></em>
RestTemplate loadBalanced() {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> RestTemplate();
}
<em><span class="hl-annotation" style="color: gray">@Primary</span></em>
<em><span class="hl-annotation" style="color: gray">@Bean</span></em>
RestTemplate restTemplate() {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> RestTemplate();
}
}
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> MyClass {
<em><span class="hl-annotation" style="color: gray">@Autowired</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">private</span> RestTemplate restTemplate;
<em><span class="hl-annotation" style="color: gray">@Autowired</span></em>
<em><span class="hl-annotation" style="color: gray">@LoadBalanced</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">private</span> RestTemplate loadBalanced;
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> String doOtherStuff() {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> loadBalanced.getForObject(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"http://stores/stores"</span>, String.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>);
}
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> String doStuff() {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> restTemplate.getForObject(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"http://example.com"</span>, String.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>);
}
}</pre><div class="important" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Important"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="images/important.png"></td><th align="left">Important</th></tr><tr><td align="left" valign="top"><p>Notice the use of the <code class="literal">@Primary</code> annotation on the plain <code class="literal">RestTemplate</code> declaration in the preceding example to disambiguate the unqualified <code class="literal">@Autowired</code> injection.</p></td></tr></table></div><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Tip"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="images/tip.png"></td><th align="left">Tip</th></tr><tr><td align="left" valign="top"><p>If you see errors such as <code class="literal">java.lang.IllegalArgumentException: Can not set org.springframework.web.client.RestTemplate field com.my.app.Foo.restTemplate to com.sun.proxy.$Proxy89</code>, try injecting <code class="literal">RestOperations</code> or setting <code class="literal">spring.aop.proxyTargetClass=true</code>.</p></td></tr></table></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="loadbalanced-webclient" href="#loadbalanced-webclient"></a>2.6&nbsp;Spring WebFlux WebClient as a Load Balancer Client</h2></div></div></div><p><code class="literal">WebClient</code> can be configured to use the <code class="literal">LoadBalancerClient</code>. <code class="literal">LoadBalancerExchangeFilterFunction</code> is auto-configured if <code class="literal">spring-webflux</code> is on the classpath. The following example shows how to configure a <code class="literal">WebClient</code> to use load balancer:</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> MyClass {
<em><span class="hl-annotation" style="color: gray">@Autowired</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">private</span> LoadBalancerExchangeFilterFunction lbFunction;
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> Mono&lt;String&gt; doOtherStuff() {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> WebClient.builder().baseUrl(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"http://stores"</span>)
.filter(lbFunction)
.build()
.get()
.uri(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"/stores"</span>)
.retrieve()
.bodyToMono(String.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>);
}
}</pre><p>The URI needs to use a virtual host name (that is, a service name, not a host name).
The <code class="literal">LoadBalancerClient</code> is used to create a full physical address.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ignore-network-interfaces" href="#ignore-network-interfaces"></a>2.7&nbsp;Ignore Network Interfaces</h2></div></div></div><p>Sometimes, it is useful to ignore certain named network interfaces so that they can be excluded from Service Discovery registration (for example, when running in a Docker container).
A list of regular expressions can be set to cause the desired network interfaces to be ignored.
The following configuration ignores the <code class="literal">docker0</code> interface and all interfaces that start with <code class="literal">veth</code>:</p><p><b>application.yml.&nbsp;</b>
</p><pre class="screen">spring:
cloud:
inetutils:
ignoredInterfaces:
- docker0
- veth.*</pre><p>
</p><p>You can also force the use of only specified network addresses by using a list of regular expressions, as shown in the following example:</p><p><b>application.yml.&nbsp;</b>
</p><pre class="screen">spring:
cloud:
inetutils:
preferredNetworks:
- 192.168
- 10.0</pre><p>
</p><p>You can also force the use of only site-local addresses, as shown in the following example:
.application.yml</p><pre class="screen">spring:
cloud:
inetutils:
useOnlySiteLocalInterfaces: true</pre><p>See <a class="link" href="https://docs.oracle.com/javase/8/docs/api/java/net/Inet4Address.html#isSiteLocalAddress--" target="_top">Inet4Address.html.isSiteLocalAddress()</a> for more details about what constitutes a site-local address.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="http-clients" href="#http-clients"></a>2.8&nbsp;HTTP Client Factories</h2></div></div></div><p>Spring Cloud Commons provides beans for creating both Apache HTTP clients (<code class="literal">ApacheHttpClientFactory</code>) and OK HTTP clients (<code class="literal">OkHttpClientFactory</code>).
The <code class="literal">OkHttpClientFactory</code> bean is created only if the OK HTTP jar is on the classpath.
In addition, Spring Cloud Commons provides beans for creating the connection managers used by both clients: <code class="literal">ApacheHttpClientConnectionManagerFactory</code> for the Apache HTTP client and <code class="literal">OkHttpClientConnectionPoolFactory</code> for the OK HTTP client.
If you would like to customize how the HTTP clients are created in downstream projects, you can provide your own implementation of these beans.
In addition, if you provide a bean of type <code class="literal">HttpClientBuilder</code> or <code class="literal">OkHttpClient.Builder</code>, the default factories use these builders as the basis for the builders returned to downstream projects.
You can also disable the creation of these beans by setting <code class="literal">spring.cloud.httpclientfactories.apache.enabled</code> or <code class="literal">spring.cloud.httpclientfactories.ok.enabled</code> to <code class="literal">false</code>.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="enabled-features" href="#enabled-features"></a>2.9&nbsp;Enabled Features</h2></div></div></div><p>Spring Cloud Commons provides a <code class="literal">/features</code> actuator endpoint.
This endpoint returns features available on the classpath and whether they are enabled.
The information returned includes the feature type, name, version, and vendor.</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_feature_types" href="#_feature_types"></a>2.9.1&nbsp;Feature types</h3></div></div></div><p>There are two types of 'features': abstract and named.</p><p>Abstract features are features where an interface or abstract class is defined and that an implementation the creates, such as <code class="literal">DiscoveryClient</code>, <code class="literal">LoadBalancerClient</code>, or <code class="literal">LockService</code>.
The abstract class or interface is used to find a bean of that type in the context.
The version displayed is <code class="literal">bean.getClass().getPackage().getImplementationVersion()</code>.</p><p>Named features are features that do not have a particular class they implement, such as "Circuit Breaker", "API Gateway", "Spring Cloud Bus", and others. These features require a name and a bean type.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_declaring_features" href="#_declaring_features"></a>2.9.2&nbsp;Declaring features</h3></div></div></div><p>Any module can declare any number of <code class="literal">HasFeature</code> beans, as shown in the following examples:</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@Bean</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> HasFeatures commonsFeatures() {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> HasFeatures.abstractFeatures(DiscoveryClient.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>, LoadBalancerClient.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>);
}
<em><span class="hl-annotation" style="color: gray">@Bean</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> HasFeatures consulFeatures() {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> HasFeatures.namedFeatures(
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> NamedFeature(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"Spring Cloud Bus"</span>, ConsulBusAutoConfiguration.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>),
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> NamedFeature(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"Circuit Breaker"</span>, HystrixCommandAspect.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>));
}
<em><span class="hl-annotation" style="color: gray">@Bean</span></em>
HasFeatures localFeatures() {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> HasFeatures.builder()
.abstractFeature(Foo.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>)
.namedFeature(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> NamedFeature(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"Bar Feature"</span>, Bar.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>))
.abstractFeature(Baz.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>)
.build();
}</pre><p>Each of these beans should go in an appropriately guarded <code class="literal">@Configuration</code>.</p></div></div></div></div></body></html>