More basic mvc documentation

docs/modules/ROOT/nav.adoc

@@ -1,4 +1,7 @@
 * xref:index.adoc[Introduction]
+
+// begin Gateway Reactive Server
+
 * xref:spring-cloud-gateway.adoc[]
 ** xref:spring-cloud-gateway/starter.adoc[]
 ** xref:spring-cloud-gateway/glossary.adoc[]
@@ -58,7 +61,16 @@
 ** xref:spring-cloud-gateway/developer-guide.adoc[]
 ** xref:spring-cloud-gateway/aot-and-native-image-support.adoc[]
 ** xref:spring-cloud-gateway/configuration-properties.adoc[]
+
+// begin Gateway Server MVC
+
 * xref:spring-cloud-gateway-server-mvc.adoc[]
 ** xref:spring-cloud-gateway-server-mvc/starter.adoc[]
+** xref:spring-cloud-gateway-server-mvc/glossary.adoc[]
+** xref:spring-cloud-gateway-server-mvc/how-it-works.adoc[]
+** xref:spring-cloud-gateway-server-mvc/java-routes-api.adoc[]
+
+// begin Gateway Proxy Exchange
+
 * xref:spring-cloud-gateway-proxy-exchange.adoc[]
 * xref:appendix.adoc[]

docs/modules/ROOT/pages/spring-cloud-gateway-server-mvc/glossary.adoc

@@ -0,0 +1,11 @@
+[[glossary]]
+= Glossary
+:page-section-summary-toc: 1
+
+* *Route*: The basic building block of the gateway.
+It is defined by an ID, a destination URI, a collection of predicates, and a collection of filters. A route is matched if the aggregate predicate is true.
+* *Predicate*: This is a https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/web/servlet/function/RequestPredicate.html[Spring WebMvc.fn `RequestPredicate`]. The input type is a https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/web/servlet/function/ServerRequest.html[Spring WebMvc.fn `ServerRequest`].
+This lets you match on anything from the HTTP request, such as headers or parameters.
+* *Filter*: These are instances of https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/web/servlet/function/HandlerFilterFunction.html[`HandlerFilterFunction`].
+Here, you can modify requests and responses before or after sending the downstream request. Filters may also implement `Function<ServerRequest, ServerRequest>` and adapted to a `HandlerFilterFunction` by https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/web/servlet/function/HandlerFilterFunction.html#ofRequestProcessor(java.util.function.Function)[`HandlerFilterFunction.ofRequestProcessor()`] for 'before' filters. For 'after' filters, `BiFunction<ServerRequest,T extends ServerResponse,R extends ServerResponse>` may be implemented and adapted by https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/web/servlet/function/HandlerFilterFunction.html#ofResponseProcessor(java.util.function.BiFunction)[`HandlerFilterFunction.ofResponseProcessor()`].
+

docs/modules/ROOT/pages/spring-cloud-gateway-server-mvc/how-it-works.adoc

@@ -0,0 +1,17 @@
+[[gateway-how-it-works]]
+= How It Works
+:page-section-summary-toc: 1
+
+The following diagram provides a high-level overview of how Spring Cloud Gateway works:
+
+// TODO: gateway mvc diagram
+//image::spring_cloud_gateway_diagram.png[Spring Cloud Gateway Diagram]
+
+In Spring Cloud Gateway Server MVC routes are normal WebMvc.fn `RouterFunction` instances with a special https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/web/servlet/function/HandlerFunction.html[HandlerFunction] to forward the requests over HTTP defined in https://github.com/spring-cloud/spring-cloud-gateway/blob/main/spring-cloud-gateway-server-mvc/src/main/java/org/springframework/cloud/gateway/server/mvc/handler/HandlerFunctions.java[org.springframework.cloud.gateway.server.mvc.handler.HandlerFunctions]. Please see the https://docs.spring.io/spring-framework/reference/web/webmvc-functional.html[WebMvc.fn] documentation for regular use of the functional API.
+
+In addition to custom `HandlerFunctions` for HTTP forwarding, Spring Cloud Gateway Server MVC provides additional `RequestPredicate` implementations in https://github.com/spring-cloud/spring-cloud-gateway/blob/main/spring-cloud-gateway-server-mvc/src/main/java/org/springframework/cloud/gateway/server/mvc/predicate/GatewayRequestPredicates.java[org.springframework.cloud.gateway.server.mvc.predicate.GatewayRequestPredicates] and `HandlerFilterFunctions` implementations in https://github.com/spring-cloud/spring-cloud-gateway/blob/main/spring-cloud-gateway-server-mvc/src/main/java/org/springframework/cloud/gateway/server/mvc/filter/FilterFunctions.java[org.springframework.cloud.gateway.server.mvc.filter.FilterFunctions]. All the custom filters that can be pure 'before' filters are implemented in https://github.com/spring-cloud/spring-cloud-gateway/blob/main/spring-cloud-gateway-server-mvc/src/main/java/org/springframework/cloud/gateway/server/mvc/filter/BeforeFilterFunctions.java[org.springframework.cloud.gateway.server.mvc.filter.BeforeFilterFunctions] and adapted in `FilterFunctions` as request processors. The custom 'after' filters in https://github.com/spring-cloud/spring-cloud-gateway/blob/main/spring-cloud-gateway-server-mvc/src/main/java/org/springframework/cloud/gateway/server/mvc/filter/AfterFilterFunctions.java[org.springframework.cloud.gateway.server.mvc.filter.AfterFilterFunctions] are also adapted in `FilterFunctions` as response processors.
+
+There are additional `*FilterFunctions` classes for optional filters that will are documented along with each filter.
+
+
+

docs/modules/ROOT/pages/spring-cloud-gateway-server-mvc/java-routes-api.adoc

@@ -0,0 +1,41 @@
+[[java-routes-api]]
+= Java Routes API
+
+Spring Cloud Gateway Server MVC uses the Spring WebMvc.fn https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/web/servlet/function/RouterFunctions.Builder.html[RouterFunctions.Builder] as the default way to create Routes, which are WebMvc.fn https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/web/servlet/function/RouterFunction.html[RouterFunction] instances.
+
+A https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/web/servlet/function/RouterFunctions.Builder.html[`RouterFunctions.Builder`] instance is obtained by calling https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/web/servlet/function/RouterFunctions.html#route()[RouterFunctions.route()]
+
+.GatewaySampleApplication.java
+[source,java]
+----
+import org.springframework.web.servlet.function.RouterFunctions.route;
+import static org.springframework.cloud.gateway.server.mvc.handler.HandlerFunctions.http;
+
+class SimpleGateway {
+    @Bean
+    public RouterFunction<ServerResponse> getRoute() {
+        return route().GET("/get", http("https://httpbin.org"));
+    }
+}
+----
+
+There are methods in `RouterFunctions.Builder` for each HTTP methods (GET, POST, etc...) combined with a path predicate, such as `/get` as above. The final parameter is the `HandlerFilterFunction`, in this case `HandlerFunctions.http()`. There are overloaded methods for each HTTP method for additional `RequestPredicate` parameters as well as a generic `route(RequestPredicate, HandlerFunction`) method for general use.
+
+[[gateway-routerfunctions-builder]]
+== Gateway MVC implementation of RouterFunctions.Builder
+
+Some advanced filters require some metadata to be added to request attributes. To accommodate this, there is a `org.springframework.cloud.gateway.server.mvc.handler.GatewayRouterFunctions` class. `GatewayRouterFunctions.route(String routeId) creates a `RouterFunctions.Builder` instance then adds a 'before' filter to add the `routeId` as request metadata.
+
+.GatewaySampleApplication.java
+[source,java]
+----
+import org.springframework.cloud.gateway.server.mvc.handler.GatewayRouterFunctions;
+import static org.springframework.cloud.gateway.server.mvc.handler.HandlerFunctions.http;
+
+class SimpleGateway {
+    @Bean
+    public RouterFunction<ServerResponse> getRoute() {
+        return route("simple_route").GET("/get", http("https://httpbin.org"));
+    }
+}
+----

docs/modules/ROOT/pages/spring-cloud-gateway-server-mvc/starter.adoc

@@ -5,9 +5,9 @@
 To include Spring Cloud Gateway Server MVC in your project, use the starter with a group ID of `org.springframework.cloud` and an artifact ID of `spring-cloud-starter-gateway-mvc`.
 See the https://projects.spring.io/spring-cloud/[Spring Cloud Project page] for details on setting up your build system with the current Spring Cloud Release Train.
 
-If you include the starter, but you do not want the gateway to be enabled, set `spring.cloud.gateway.enabled=false`.
+If you include the starter, but you do not want the gateway to be enabled, set `spring.cloud.gateway.mvc.enabled=false`.
 
-IMPORTANT: Spring Cloud Gateway Server MVC is built on https://spring.io/projects/spring-boot#learn[Spring Boot] and https://docs.spring.io/spring-framework/reference/web.html[Spring Web MVC].
+IMPORTANT: Spring Cloud Gateway Server MVC is built on https://spring.io/projects/spring-boot#learn[Spring Boot] and https://docs.spring.io/spring-framework/reference/web/webmvc-functional.html[Spring WebMvc.fn].
 As a consequence, many of the asynchronous or reactive libraries may not apply when you use Spring Cloud Gateway Server MVC.
 
 IMPORTANT: Spring Cloud Gateway Server MVC works with traditional Servlet runtimes such as Tomcat and Jetty.

spring-cloud-gateway-server-mvc/src/main/java/org/springframework/cloud/gateway/server/mvc/GatewayServerMvcAutoConfiguration.java

@@ -19,6 +19,7 @@ package org.springframework.cloud.gateway.server.mvc;
 import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.boot.autoconfigure.AutoConfiguration;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.boot.autoconfigure.web.client.RestClientAutoConfiguration;
 import org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration;
 import org.springframework.boot.ssl.SslBundle;
@@ -51,6 +52,7 @@ import org.springframework.util.StringUtils;
 import org.springframework.web.client.RestClient;
 
 @AutoConfiguration(after = { RestTemplateAutoConfiguration.class, RestClientAutoConfiguration.class })
+@ConditionalOnProperty(name = "spring.cloud.gateway.mvc.enabled", matchIfMissing = true)
 @Import(GatewayMvcPropertiesBeanDefinitionRegistrar.class)
 public class GatewayServerMvcAutoConfiguration {