Add documentation for WebMvc.fn

See gh-29683

spring-boot-project/spring-boot-docs/src/docs/asciidoc/features/developing-web-applications.adoc

@@ -22,13 +22,27 @@ The following code shows a typical `@RestController` that serves JSON data:
 include::{docs-java}/features/developingwebapplications/springmvc/MyRestController.java[]
 ----
 
+"`WebMvc.fn`", the functional variant, separates the routing configuration from the actual handling of the requests, as shown in the following example:
+
+[source,java,indent=0,subs="verbatim"]
+----
+include::{docs-java}/features/developingwebapplications/springmvc/MyRoutingConfiguration.java[]
+----
+
+[source,java,indent=0,subs="verbatim"]
+----
+include::{docs-java}/features/developingwebapplications/springmvc/MyUserHandler.java[]
+----
+
 Spring MVC is part of the core Spring Framework, and detailed information is available in the  {spring-framework-docs}/web.html#mvc[reference documentation].
 There are also several guides that cover Spring MVC available at https://spring.io/guides.
 
-
+TIP: You can define as many `RouterFunction` beans as you like to modularize the definition of the router.
+Beans can be ordered if you need to apply a precedence.
 
 [[features.developing-web-applications.spring-mvc.auto-configuration]]
 ==== Spring MVC Auto-configuration
+
 Spring Boot provides auto-configuration for Spring MVC that works well with most applications.
 
 The auto-configuration adds the following features on top of Spring's defaults:

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/features/developingwebapplications/springmvc/MyRoutingConfiguration.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2012-2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.features.developingwebapplications.springmvc;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.http.MediaType;
+import org.springframework.web.servlet.function.RequestPredicate;
+import org.springframework.web.servlet.function.RouterFunction;
+import org.springframework.web.servlet.function.ServerResponse;
+
+import static org.springframework.web.servlet.function.RequestPredicates.accept;
+import static org.springframework.web.servlet.function.RouterFunctions.route;
+
+@Configuration(proxyBeanMethods = false)
+public class MyRoutingConfiguration {
+
+	private static final RequestPredicate ACCEPT_JSON = accept(MediaType.APPLICATION_JSON);
+
+	@Bean
+	public RouterFunction<ServerResponse> routerFunction(MyUserHandler userHandler) {
+		// @formatter:off
+		return route()
+				.GET("/{user}", ACCEPT_JSON, userHandler::getUser)
+				.GET("/{user}/customers", ACCEPT_JSON, userHandler::getUserCustomers)
+				.DELETE("/{user}", ACCEPT_JSON, userHandler::deleteUser)
+				.build();
+		// @formatter:on
+	}
+
+}

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/features/developingwebapplications/springmvc/MyUserHandler.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2012-2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.docs.features.developingwebapplications.springmvc;
+
+import org.springframework.stereotype.Component;
+import org.springframework.web.servlet.function.ServerRequest;
+import org.springframework.web.servlet.function.ServerResponse;
+
+@Component
+public class MyUserHandler {
+
+	public ServerResponse getUser(ServerRequest request) {
+		/**/ return ServerResponse.ok().build();
+	}
+
+	public ServerResponse getUserCustomers(ServerRequest request) {
+		/**/ return ServerResponse.ok().build();
+	}
+
+	public ServerResponse deleteUser(ServerRequest request) {
+		/**/ return ServerResponse.ok().build();
+	}
+
+}

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/features/developingwebapplications/springwebflux/MyRoutingConfiguration.java

@@ -23,8 +23,6 @@ import org.springframework.web.reactive.function.server.RequestPredicate;
 import org.springframework.web.reactive.function.server.RouterFunction;
 import org.springframework.web.reactive.function.server.ServerResponse;
 
-import static org.springframework.web.reactive.function.server.RequestPredicates.DELETE;
-import static org.springframework.web.reactive.function.server.RequestPredicates.GET;
 import static org.springframework.web.reactive.function.server.RequestPredicates.accept;
 import static org.springframework.web.reactive.function.server.RouterFunctions.route;
 
@@ -36,10 +34,11 @@ public class MyRoutingConfiguration {
 	@Bean
 	public RouterFunction<ServerResponse> monoRouterFunction(MyUserHandler userHandler) {
 		// @formatter:off
-		return route(
-				GET("/{user}").and(ACCEPT_JSON), userHandler::getUser).andRoute(
-				GET("/{user}/customers").and(ACCEPT_JSON), userHandler::getUserCustomers).andRoute(
-				DELETE("/{user}").and(ACCEPT_JSON), userHandler::deleteUser);
+		return route()
+				.GET("/{user}", ACCEPT_JSON, userHandler::getUser)
+				.GET("/{user}/customers", ACCEPT_JSON, userHandler::getUserCustomers)
+				.DELETE("/{user}", ACCEPT_JSON, userHandler::deleteUser)
+				.build();
 		// @formatter:on
 	}
 

src/checkstyle/checkstyle-suppressions.xml

@@ -20,6 +20,7 @@
 	<suppress files="[\\/]spring-boot-docs[\\/]" checks="JavadocType|JavadocVariable" />
 	<suppress files="[\\/]spring-boot-docs[\\/]" checks="SpringJavadoc" message="\@since" />
 	<suppress files="[\\/]spring-boot-docs[\\/].*jooq" checks="AvoidStaticImport" />
+	<suppress files="[\\/]spring-boot-docs[\\/].*MyRoutingConfiguration\.java" checks="AvoidStaticImport"/>
 	<suppress files="[\\/]spring-boot-smoke-tests[\\/]" checks="JavadocType" />
 	<suppress files="[\\/]spring-boot-smoke-tests[\\/]" checks="ImportControl" />
 	<suppress files="[\\/]spring-boot-smoke-tests[\\/]" id="mainCodeIllegalImportCheck" />