Document UrlHandler Servlet and reactive filters

Closes gh-33784

Author: bclozel

framework-docs/modules/ROOT/pages/web/webflux/reactive-spring.adoc

@@ -419,6 +419,24 @@ controllers. However, when you use it with Spring Security, we advise relying on
 
 See the section on xref:web/webflux-cors.adoc[CORS] and the xref:web/webflux-cors.adoc#webflux-cors-webfilter[CORS `WebFilter`] for more details.
 
+[[filters.url-handler]]
+=== URL Handler
+[.small]#xref:web/webmvc/filters.adoc#filters.url-handler[See equivalent in the Servlet stack]#
+
+You may want your controller endpoints to match routes with or without a trailing slash in the URL path.
+For example, both "GET /home" and "GET /home/" should be handled by a controller method annotated with `@GetMapping("/home")`.
+
+Adding trailing slash variants to all mapping declarations is not the best way to handle this use case.
+The `UrlHandlerFilter` web filter has been designed for this purpose. It can be configured to:
+
+* respond with an HTTP redirect status when receiving URLs with trailing slashes, sending browsers to the non-trailing slash URL variant.
+* mutate the request to act as if the request was sent without a trailing slash and continue the processing of the request.
+
+Here is how you can instantiate and configure a `UrlHandlerFilter` for a blog application:
+
+include-code::./UrlHandlerFilterConfiguration[tag=config,indent=0]
+
+
 
 [[webflux-exception-handler]]
 == Exceptions

framework-docs/modules/ROOT/pages/web/webmvc/filters.adoc

@@ -9,7 +9,11 @@ The `spring-web` module provides some useful filters:
 * xref:web/webmvc/filters.adoc#filters-forwarded-headers[Forwarded Headers]
 * xref:web/webmvc/filters.adoc#filters-shallow-etag[Shallow ETag]
 * xref:web/webmvc/filters.adoc#filters-cors[CORS]
+* xref:web/webmvc/filters.adoc#filters.url-handler[URL Handler]
 
+Servlet filters can be configured in the `web.xml` configuration file or using Servlet annotations.
+If you are using Spring Boot, you can
+{spring-boot-docs}/how-to/webserver.html#howto.webserver.add-servlet-filter-listener.spring-bean[declare them as beans and configure them as part of your application].
 
 
 [[filters-http-put]]
@@ -109,4 +113,22 @@ See the sections on xref:web/webmvc-cors.adoc[CORS] and the xref:web/webmvc-cors
 
 
 
+[[filters.url-handler]]
+== URL Handler
+[.small]#xref:web/webflux/reactive-spring.adoc#filters.url-handler[See equivalent in the Reactive stack]#
+
+In previous Spring Framework versions, Spring MVC could be configured to ignore trailing slashes in URL paths
+when mapping incoming requests on controller methods. This could be done by enabling the `setUseTrailingSlashMatch`
+option on the `PathMatchConfigurer`. This means that sending a "GET /home/" request would be handled by a controller
+method annotated with `@GetMapping("/home")`.
+
+This option has been retired, but applications are still expected to handle such requests in a safe way.
+The `UrlHandlerFilter` Servlet filter has been designed for this purpose. It can be configured to:
+
+* respond with an HTTP redirect status when receiving URLs with trailing slashes, sending browsers to the non-trailing slash URL variant.
+* wrap the request to act as if the request was sent without a trailing slash and continue the processing of the request.
+
+Here is how you can instantiate and configure a `UrlHandlerFilter` for a blog application:
+
+include-code::./UrlHandlerFilterConfiguration[tag=config,indent=0]
 

framework-docs/src/main/java/org/springframework/docs/web/webflux/filters/urlhandler/UrlHandlerFilterConfiguration.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2002-2024 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.docs.web.webflux.filters.urlhandler;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.web.filter.reactive.UrlHandlerFilter;
+
+public class UrlHandlerFilterConfiguration {
+
+	public void configureUrlHandlerFilter() {
+		// tag::config[]
+		UrlHandlerFilter urlHandlerFilter = UrlHandlerFilter
+				// will HTTP 308 redirect "/blog/my-blog-post/" -> "/blog/my-blog-post"
+				.trailingSlashHandler("/blog/**").redirect(HttpStatus.PERMANENT_REDIRECT)
+				// will mutate the request to "/admin/user/account/" and make it as "/admin/user/account"
+				.trailingSlashHandler("/admin/**").mutateRequest()
+				.build();
+		// end::config[]
+	}
+}

framework-docs/src/main/java/org/springframework/docs/web/webmvc/filters/urlhandler/UrlHandlerFilterConfiguration.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2002-2024 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.docs.web.webmvc.filters.urlhandler;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.web.filter.UrlHandlerFilter;
+
+public class UrlHandlerFilterConfiguration {
+
+	public void configureUrlHandlerFilter() {
+		// tag::config[]
+		UrlHandlerFilter urlHandlerFilter = UrlHandlerFilter
+				// will HTTP 308 redirect "/blog/my-blog-post/" -> "/blog/my-blog-post"
+				.trailingSlashHandler("/blog/**").redirect(HttpStatus.PERMANENT_REDIRECT)
+				// will wrap the request to "/admin/user/account/" and make it as "/admin/user/account"
+				.trailingSlashHandler("/admin/**").wrapRequest()
+				.build();
+		// end::config[]
+	}
+}

framework-docs/src/main/kotlin/org/springframework/docs/web/webflux/filters/urlhandler/UrlHandlerFilterConfiguration.kt

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2002-2024 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.docs.web.webflux.filters.urlhandler
+
+import org.springframework.http.HttpStatus
+import org.springframework.web.filter.reactive.UrlHandlerFilter
+
+class UrlHandlerFilterConfiguration {
+
+	fun configureUrlHandlerFilter() {
+		// tag::config[]
+		val urlHandlerFilter = UrlHandlerFilter
+			// will HTTP 308 redirect "/blog/my-blog-post/" -> "/blog/my-blog-post"
+			.trailingSlashHandler("/blog/**").redirect(HttpStatus.PERMANENT_REDIRECT)
+			// will mutate the request to "/admin/user/account/" and make it as "/admin/user/account"
+			.trailingSlashHandler("/admin/**").mutateRequest()
+			.build()
+		// end::config[]
+	}
+}

framework-docs/src/main/kotlin/org/springframework/docs/web/webmvc/filters/urlhandler/UrlHandlerFilterConfiguration.kt

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2002-2024 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.docs.web.webmvc.filters.urlhandler
+
+import org.springframework.http.HttpStatus
+import org.springframework.web.filter.UrlHandlerFilter
+
+class UrlHandlerFilterConfiguration {
+
+	fun configureUrlHandlerFilter() {
+		// tag::config[]
+		val urlHandlerFilter = UrlHandlerFilter
+				// will HTTP 308 redirect "/blog/my-blog-post/" -> "/blog/my-blog-post"
+				.trailingSlashHandler("/blog/**").redirect(HttpStatus.PERMANENT_REDIRECT)
+				// will wrap the request to "/admin/user/account/" and make it as "/admin/user/account"
+				.trailingSlashHandler("/admin/**").wrapRequest()
+				.build()
+		// end::config[]
+	}
+}