Log warning if multiple @⁠RequestMapping annotations are declared

If multiple request mapping annotations are discovered, Spring MVC and
Spring WebFlux now log a warning similar to the following (without
newlines).

Multiple @⁠RequestMapping annotations found on
void org.example.MyController.put(), but only the first will be used:
[
@⁠org.springframework.web.bind.annotation.PutMapping(consumes={}, headers={}, name="", params={}, path={"/put"}, produces={}, value={"/put"}),
@⁠org.springframework.web.bind.annotation.PostMapping(consumes={}, headers={}, name="", params={}, path={"/put"}, produces={}, value={"/put"})
]

Closes gh-31962

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * 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.
@@ -16,18 +16,23 @@
 
 package org.springframework.web.reactive.result.method.annotation;
 
+import java.lang.annotation.Annotation;
 import java.lang.reflect.AnnotatedElement;
 import java.lang.reflect.Method;
 import java.lang.reflect.Parameter;
 import java.util.Collections;
 import java.util.LinkedHashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.function.Predicate;
 
 import org.springframework.context.EmbeddedValueResolverAware;
 import org.springframework.core.annotation.AnnotatedElementUtils;
 import org.springframework.core.annotation.MergedAnnotation;
+import org.springframework.core.annotation.MergedAnnotationPredicates;
 import org.springframework.core.annotation.MergedAnnotations;
+import org.springframework.core.annotation.MergedAnnotations.SearchStrategy;
+import org.springframework.core.annotation.RepeatableContainers;
 import org.springframework.lang.Nullable;
 import org.springframework.stereotype.Controller;
 import org.springframework.util.Assert;
@@ -182,9 +187,20 @@ public class RequestMappingHandlerMapping extends RequestMappingInfoHandlerMappi
 		RequestCondition<?> customCondition = (element instanceof Class<?> clazz ?
 				getCustomTypeCondition(clazz) : getCustomMethodCondition((Method) element));
 
-		RequestMapping requestMapping = AnnotatedElementUtils.findMergedAnnotation(element, RequestMapping.class);
-		if (requestMapping != null) {
-			return createRequestMappingInfo(requestMapping, customCondition);
+		MergedAnnotations mergedAnnotations = MergedAnnotations.from(element, SearchStrategy.TYPE_HIERARCHY,
+				RepeatableContainers.none());
+		List<AnnotationDescriptor<RequestMapping>> requestMappings = mergedAnnotations.stream(RequestMapping.class)
+				.filter(MergedAnnotationPredicates.firstRunOf(MergedAnnotation::getAggregateIndex))
+				.map(AnnotationDescriptor::new)
+				.distinct()
+				.toList();
+
+		if (!requestMappings.isEmpty()) {
+			if (requestMappings.size() > 1 && logger.isWarnEnabled()) {
+				logger.warn("Multiple @RequestMapping annotations found on %s, but only the first will be used: %s"
+							.formatted(element, requestMappings));
+			}
+			return createRequestMappingInfo(requestMappings.get(0).annotation, customCondition);
 		}
 
 		HttpExchange httpExchange = AnnotatedElementUtils.findMergedAnnotation(element, HttpExchange.class);
@@ -414,4 +430,32 @@ public class RequestMappingHandlerMapping extends RequestMappingInfoHandlerMappi
 		}
 	}
 
+	private static class AnnotationDescriptor<A extends Annotation> {
+
+		private final A annotation;
+		private final Annotation source;
+
+		AnnotationDescriptor(MergedAnnotation<A> mergedAnnotation) {
+			this.annotation = mergedAnnotation.synthesize();
+			this.source = (mergedAnnotation.getDistance() > 0 ?
+					mergedAnnotation.getRoot().synthesize() : this.annotation);
+		}
+
+		@Override
+		public boolean equals(Object obj) {
+			return (obj instanceof AnnotationDescriptor<?> that && this.annotation.equals(that.annotation));
+		}
+
+		@Override
+		public int hashCode() {
+			return this.annotation.hashCode();
+		}
+
+		@Override
+		public String toString() {
+			return this.source.toString();
+		}
+
+	}
+
 }

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

@@ -36,7 +36,6 @@ import org.springframework.web.bind.annotation.DeleteMapping;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PatchMapping;
 import org.springframework.web.bind.annotation.PostMapping;
-import org.springframework.web.bind.annotation.PutMapping;
 import org.springframework.web.bind.annotation.RequestBody;
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RequestMethod;
@@ -60,6 +59,7 @@ import static org.mockito.Mockito.mock;
  *
  * @author Rossen Stoyanchev
  * @author Olga Maciaszek-Sharma
+ * @author Sam Brannen
  */
 class RequestMappingHandlerMappingTests {
 
@@ -231,7 +231,9 @@ class RequestMappingHandlerMappingTests {
 
 
 	@Controller @SuppressWarnings("unused")
+	// gh-31962: The presence of multiple @RequestMappings is intentional.
 	@RequestMapping(consumes = MediaType.APPLICATION_JSON_VALUE)
+	@ExtraRequestMapping
 	static class ComposedAnnotationController {
 
 		@RequestMapping
@@ -250,7 +252,10 @@ class RequestMappingHandlerMappingTests {
 		public void post(@RequestBody(required = false) Foo foo) {
 		}
 
-		@PutMapping("/put")
+		// gh-31962: The presence of multiple @RequestMappings is intentional.
+		@PatchMapping("/put")
+		@RequestMapping(path = "/put", method = RequestMethod.PUT) // local @RequestMapping overrides meta-annotations
+		@PostMapping("/put")
 		public void put() {
 		}
 
@@ -267,6 +272,13 @@ class RequestMappingHandlerMappingTests {
 	}
 
 
+	@RequestMapping
+	@Target(ElementType.TYPE)
+	@Retention(RetentionPolicy.RUNTIME)
+	@interface ExtraRequestMapping {
+	}
+
+
 	@RequestMapping(method = RequestMethod.POST,
 			produces = MediaType.APPLICATION_JSON_VALUE,
 			consumes = MediaType.APPLICATION_JSON_VALUE)