Method level only, empty RequestMapping matches "" and "/"

Closes spring-projectsgh-30293

spring-test/src/test/java/org/springframework/test/web/reactive/server/DefaultControllerSpecTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -48,15 +48,12 @@ public void controller() {
 				.exchange()
 				.expectStatus().isOk()
 				.expectBody(String.class).isEqualTo("Success");
-	}
 
-	@Test
-	public void controllerEmptyPath() {
 		new DefaultControllerSpec(new MyController()).build()
 				.get().uri("")
 				.exchange()
 				.expectStatus().isOk()
-				.expectBody(String.class).isEqualTo("Success empty path");
+				.expectBody(String.class).isEqualTo("Success");
 	}
 
 	@Test
@@ -121,19 +118,15 @@ public void uriTemplate() {
 	}
 
 
+	@SuppressWarnings("unused")
 	@RestController
 	private static class MyController {
 
-		@GetMapping("/")
+		@GetMapping
 		public String handleRootPath() {
 			return "Success";
 		}
 
-		@GetMapping
-		public String handleEmptyPath() {
-			return "Success empty path";
-		}
-
 		@GetMapping("/exception")
 		public void handleWithError() {
 			throw new IllegalStateException();

spring-webflux/src/main/java/org/springframework/web/reactive/result/condition/PatternsRequestCondition.java

@@ -89,8 +89,12 @@ protected String getToStringInfix() {
 		return " || ";
 	}
 
-	private boolean isEmptyPathMapping() {
-		return this.patterns == EMPTY_PATH_PATTERN;
+	/**
+	 * Whether the condition is the "" (empty path) mapping.
+	 * @since 6.0.10
+	 */
+	public boolean isEmptyPathMapping() {
+		return (this.patterns == EMPTY_PATH_PATTERN);
 	}
 
 	/**

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/RequestMappingHandlerMapping.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -153,6 +153,9 @@ protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handler
 			if (typeInfo != null) {
 				info = typeInfo.combine(info);
 			}
+			if (info.getPatternsCondition().isEmptyPathMapping()) {
+				info = info.mutate().paths("", "/").options(this.config).build();
+			}
 			for (Map.Entry<String, Predicate<Class<?>>> entry : this.pathPrefixes.entrySet()) {
 				if (entry.getValue().test(handlerType)) {
 					String prefix = entry.getKey();

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/RequestMappingIntegrationTests.java

@@ -61,6 +61,17 @@ protected ApplicationContext initApplicationContext() {
 	}
 
 
+	@ParameterizedHttpServerTest // gh-30293
+	void emptyMapping(HttpServer httpServer) throws Exception {
+		startServer(httpServer);
+
+		String url = "http://localhost:" + this.port;
+		assertThat(getRestTemplate().getForObject(url, String.class)).isEqualTo("root");
+
+		url += "/";
+		assertThat(getRestTemplate().getForObject(url, String.class)).isEqualTo("root");
+	}
+
 	@ParameterizedHttpServerTest
 	void httpHead(HttpServer httpServer) throws Exception {
 		startServer(httpServer);
@@ -106,6 +117,11 @@ static class WebConfig {
 	@SuppressWarnings("unused")
 	private static class TestRestController {
 
+		@GetMapping
+		public String get() {
+			return "root";
+		}
+
 		@GetMapping("/text")
 		public String textGet() {
 			return "Foo";

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/RequestMappingInfo.java

@@ -255,6 +255,16 @@ public Set<String> getPatternValues() {
 				pprc.getPatternValues() : ((PatternsRequestCondition) condition).getPatterns());
 	}
 
+	/**
+	 * Whether the request mapping has an empty URL path mapping.
+	 * @since 6.0.10
+	 */
+	public boolean isEmptyMapping() {
+		RequestCondition<?> condition = getActivePatternsCondition();
+		return (condition instanceof PathPatternsRequestCondition pprc ?
+				pprc.isEmptyPathMapping() : ((PatternsRequestCondition) condition).isEmptyPathMapping());
+	}
+
 	/**
 	 * Return the HTTP request methods of this {@link RequestMappingInfo};
 	 * or instance with 0 request methods (never {@code null}).

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/RequestMappingHandlerMapping.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -305,6 +305,9 @@ protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handler
 			if (typeInfo != null) {
 				info = typeInfo.combine(info);
 			}
+			if (info.isEmptyMapping()) {
+				info = info.mutate().paths("", "/").options(this.config).build();
+			}
 			String prefix = getPathPrefix(handlerType);
 			if (prefix != null) {
 				info = RequestMappingInfo.paths(prefix).options(this.config).build().combine(info);

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/ServletAnnotationControllerHandlerMethodTests.java

@@ -193,7 +193,16 @@ void emptyValueMapping(boolean usePathPatterns) throws Exception {
 		request.setServletPath("");
 		MockHttpServletResponse response = new MockHttpServletResponse();
 		getServlet().service(request, response);
+
+		assertThat(response.getContentAsString()).isEqualTo("test");
+
+		// gh-30293
+		request = new MockHttpServletRequest("GET", "/");
+		response = new MockHttpServletResponse();
+		getServlet().service(request, response);
+
 		assertThat(response.getContentAsString()).isEqualTo("test");
+
 	}
 
 	@PathPatternsParameterizedTest