ResponseEntity declared as Object in WebFlux controller

Issue: SPR-15785

Author: rstoyanchev

spring-webflux/src/main/java/org/springframework/web/reactive/HandlerResult.java

@@ -92,15 +92,18 @@ public Object getReturnValue() {
 	}
 
 	/**
-	 * Return the type of the value returned from the handler.
+	 * Return the type of the value returned from the handler -- e.g. the return
+	 * type declared on a controller method's signature. Also see
+	 * {@link #getReturnTypeSource()} to obtain the underlying
+	 * {@link MethodParameter} for the return type.
 	 */
 	public ResolvableType getReturnType() {
 		return this.returnType;
 	}
 
 	/**
-	 * Return the {@link MethodParameter} from which
-	 * {@link #getReturnType() returnType} was created.
+	 * Return the {@link MethodParameter} from which {@link #getReturnType()
+	 * returnType} was created.
 	 */
 	public MethodParameter getReturnTypeSource() {
 		return (MethodParameter) this.returnType.getSource();

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

@@ -80,14 +80,25 @@ public ResponseEntityResultHandler(List<HttpMessageWriter<?>> writers,
 
 	@Override
 	public boolean supports(HandlerResult result) {
-		if (isSupportedType(result.getReturnType().getRawClass())) {
+		Class<?> valueType = resolveReturnValueType(result);
+		if (isSupportedType(valueType)) {
 			return true;
 		}
 		ReactiveAdapter adapter = getAdapter(result);
 		return adapter != null && !adapter.isNoValue() &&
 				isSupportedType(result.getReturnType().getGeneric().resolve(Object.class));
 	}
 
+	@Nullable
+	private static Class<?> resolveReturnValueType(HandlerResult result) {
+		Class<?> valueType = result.getReturnType().getRawClass();
+		Object value = result.getReturnValue();
+		if ((valueType == null || valueType.equals(Object.class)) && value != null) {
+			valueType = value.getClass();
+		}
+		return valueType;
+	}
+
 	private boolean isSupportedType(@Nullable Class<?> clazz) {
 		return (clazz != null && HttpEntity.class.isAssignableFrom(clazz) &&
 				!RequestEntity.class.isAssignableFrom(clazz));

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

@@ -120,6 +120,11 @@ public void supports() throws NoSuchMethodException {
 
 		returnType = on(TestController.class).resolveReturnType(CompletableFuture.class, entity(String.class));
 		assertTrue(this.resultHandler.supports(handlerResult(value, returnType)));
+
+		// SPR-15785
+		value = ResponseEntity.ok("testing");
+		returnType = on(TestController.class).resolveReturnType(Object.class);
+		assertTrue(this.resultHandler.supports(handlerResult(value, returnType)));
 	}
 
 	@Test
@@ -190,6 +195,9 @@ public void handleReturnTypes() throws Exception {
 		MethodParameter returnType = on(TestController.class).resolveReturnType(entity(String.class));
 		testHandle(returnValue, returnType);
 
+		returnType = on(TestController.class).resolveReturnType(Object.class);
+		testHandle(returnValue, returnType);
+
 		returnValue = Mono.just(ok("abc"));
 		returnType = on(TestController.class).resolveReturnType(Mono.class, entity(String.class));
 		testHandle(returnValue, returnType);
@@ -387,6 +395,9 @@ private static class TestController {
 		Mono<ResponseEntity<?>> monoResponseEntityWildcard() { return null; }
 
 		Flux<?> fluxWildcard() { return null; }
+
+		Object object() { return null; }
+
 	}
 
 }