Log warning if @RequestMapping method has no explicit mapping

Commit c0b52d09f5 introduced support for
throwing an exception if a @RequestMapping handler method in a Spring
MVC controller was mapped to an empty path. This had negative side
effects for applications that intentionally mapped to an empty path,
potentially alongside a mapping to an explicit path for the same
handler method.

This commit addresses this by logging a warning (instead of throwing an
exception) if a @RequestMapping method is mapped only to empty paths.

This commit also introduces the same support for WebFlux-based
@RequestMapping handler methods.

Closes gh-22543

spring-webmvc/src/main/java/org/springframework/web/servlet/handler/AbstractHandlerMethodMapping.java

@@ -62,7 +62,7 @@ import org.springframework.web.servlet.HandlerMapping;
  * @author Sam Brannen
  * @since 3.1
  * @param <T> the mapping for a {@link HandlerMethod} containing the conditions
- * needed to match the handler method to incoming request.
+ * needed to match the handler method to an incoming request.
  */
 public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMapping implements InitializingBean {
 
@@ -496,7 +496,7 @@ public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMap
 	protected abstract T getMappingForMethod(Method method, Class<?> handlerType);
 
 	/**
-	 * Extract and return the URL paths contained in a mapping.
+	 * Extract and return the URL paths contained in the supplied mapping.
 	 */
 	protected abstract Set<String> getMappingPathPatterns(T mapping);
 
@@ -616,11 +616,11 @@ public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMap
 		}
 
 		private void validateMethodMapping(HandlerMethod handlerMethod, T mapping) {
-			// Assert that the supplied mapping maps the supplied HandlerMethod
-			// to explicit, non-empty paths.
-			if (!getMappingPathPatterns(mapping).stream().allMatch(StringUtils::hasText)) {
-				throw new IllegalStateException(String.format("Missing path mapping. " +
-						"Handler method '%s' in bean '%s' must be mapped to a non-empty path. " +
+			// Log a warning if the supplied mapping maps the supplied HandlerMethod
+			// only to empty paths.
+			if (logger.isWarnEnabled() && getMappingPathPatterns(mapping).stream().noneMatch(StringUtils::hasText)) {
+				logger.warn(String.format(
+						"Handler method '%s' in bean '%s' is not mapped to an explicit path. " +
 						"If you wish to map to all paths, please map explicitly to \"/**\" or \"**\".",
 						handlerMethod, handlerMethod.getBean()));
 			}

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

@@ -75,7 +75,7 @@ public abstract class RequestMappingInfoHandlerMapping extends AbstractHandlerMe
 
 
 	/**
-	 * Get the URL path patterns associated with this {@link RequestMappingInfo}.
+	 * Get the URL path patterns associated with the supplied {@link RequestMappingInfo}.
 	 */
 	@Override
 	protected Set<String> getMappingPathPatterns(RequestMappingInfo info) {

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

@@ -797,11 +797,28 @@ public class ServletAnnotationControllerHandlerMethodTests extends AbstractServl
 	}
 
 	@Test
-	public void unmappedPathMapping() {
-		assertThatThrownBy(() -> initServletWithControllers(UnmappedPathController.class))
-			.isInstanceOf(BeanCreationException.class)
-			.hasCauseInstanceOf(IllegalStateException.class)
-			.hasMessageContaining("Missing path mapping");
+	public void unmappedPathMapping() throws Exception {
+		initServletWithControllers(UnmappedPathController.class);
+
+		MockHttpServletRequest request = new MockHttpServletRequest("GET", "/bogus-unmapped");
+		MockHttpServletResponse response = new MockHttpServletResponse();
+		getServlet().service(request, response);
+		assertEquals("get", response.getContentAsString());
+	}
+
+	@Test
+	public void explicitAndEmptyPathsControllerMapping() throws Exception {
+		initServletWithControllers(ExplicitAndEmptyPathsController.class);
+
+		MockHttpServletRequest request = new MockHttpServletRequest("GET", "/");
+		MockHttpServletResponse response = new MockHttpServletResponse();
+		getServlet().service(request, response);
+		assertEquals("get", response.getContentAsString());
+
+		request = new MockHttpServletRequest("GET", "");
+		response = new MockHttpServletResponse();
+		getServlet().service(request, response);
+		assertEquals("get", response.getContentAsString());
 	}
 
 	@Test
@@ -2733,11 +2750,22 @@ public class ServletAnnotationControllerHandlerMethodTests extends AbstractServl
 	}
 
 	@Controller
-	@RequestMapping // path intentionally omitted
+	// @RequestMapping intentionally omitted
 	static class UnmappedPathController {
 
 		@GetMapping // path intentionally omitted
-		public void get(@RequestParam(required = false) String id) {
+		public void get(Writer writer) throws IOException {
+			writer.write("get");
+		}
+	}
+
+	@Controller
+	// @RequestMapping intentionally omitted
+	static class ExplicitAndEmptyPathsController {
+
+		@GetMapping({"/", ""})
+		public void get(Writer writer) throws IOException {
+			writer.write("get");
 		}
 	}