WebFlux supporst HttpHeaders return values

Issue: SPR-16006

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

@@ -28,6 +28,7 @@ import org.springframework.core.ReactiveAdapterRegistry;
 import org.springframework.http.HttpEntity;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
+import org.springframework.http.HttpStatus;
 import org.springframework.http.RequestEntity;
 import org.springframework.http.ResponseEntity;
 import org.springframework.http.codec.HttpMessageWriter;
@@ -100,8 +101,9 @@ public class ResponseEntityResultHandler extends AbstractMessageWriterResultHand
 	}
 
 	private boolean isSupportedType(@Nullable Class<?> clazz) {
-		return (clazz != null && HttpEntity.class.isAssignableFrom(clazz) &&
+		return (clazz != null && ((HttpEntity.class.isAssignableFrom(clazz) &&
-				!RequestEntity.class.isAssignableFrom(clazz));
+				!RequestEntity.class.isAssignableFrom(clazz)) ||
+				HttpHeaders.class.isAssignableFrom(clazz)));
 	}
 
 
@@ -123,8 +125,17 @@ public class ResponseEntityResultHandler extends AbstractMessageWriterResultHand
 		}
 
 		return returnValueMono.flatMap(returnValue -> {
-			Assert.isInstanceOf(HttpEntity.class, returnValue, "HttpEntity expected");
+			HttpEntity<?> httpEntity;
-			HttpEntity<?> httpEntity = (HttpEntity<?>) returnValue;
+			if (returnValue instanceof HttpEntity) {
+				httpEntity = (HttpEntity<?>) returnValue;
+			}
+			else if (returnValue instanceof HttpHeaders) {
+				httpEntity = new ResponseEntity<Void>((HttpHeaders) returnValue, HttpStatus.OK);
+			}
+			else {
+				throw new IllegalArgumentException(
+						"HttpEntity or HttpHeaders expected but got: " + returnValue.getClass());
+			}
 
 			if (httpEntity instanceof ResponseEntity) {
 				ResponseEntity<?> responseEntity = (ResponseEntity<?>) httpEntity;
@@ -139,7 +150,8 @@ public class ResponseEntityResultHandler extends AbstractMessageWriterResultHand
 						.filter(entry -> !responseHeaders.containsKey(entry.getKey()))
 						.forEach(entry -> responseHeaders.put(entry.getKey(), entry.getValue()));
 			}
-			if(httpEntity.getBody() == null) {
+
+			if(httpEntity.getBody() == null || returnValue instanceof HttpHeaders) {
 				return exchange.getResponse().setComplete();
 			}
 

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

@@ -24,6 +24,7 @@ import java.time.temporal.ChronoUnit;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.concurrent.CompletableFuture;
 
@@ -41,6 +42,7 @@ import org.springframework.core.codec.ByteBufferEncoder;
 import org.springframework.core.codec.CharSequenceEncoder;
 import org.springframework.core.io.buffer.support.DataBufferTestUtils;
 import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
 import org.springframework.http.codec.EncoderHttpMessageWriter;
@@ -121,6 +123,9 @@ public class ResponseEntityResultHandlerTests {
 		returnType = on(TestController.class).resolveReturnType(CompletableFuture.class, entity(String.class));
 		assertTrue(this.resultHandler.supports(handlerResult(value, returnType)));
 
+		returnType = on(TestController.class).resolveReturnType(HttpHeaders.class);
+		assertTrue(this.resultHandler.supports(handlerResult(value, returnType)));
+
 		// SPR-15785
 		value = ResponseEntity.ok("testing");
 		returnType = on(TestController.class).resolveReturnType(Object.class);
@@ -150,7 +155,7 @@ public class ResponseEntityResultHandlerTests {
 	}
 
 	@Test
-	public void statusCode() throws Exception {
+	public void responseEntityStatusCode() throws Exception {
 		ResponseEntity<Void> value = ResponseEntity.noContent().build();
 		MethodParameter returnType = on(TestController.class).resolveReturnType(entity(Void.class));
 		HandlerResult result = handlerResult(value, returnType);
@@ -163,7 +168,22 @@ public class ResponseEntityResultHandlerTests {
 	}
 
 	@Test
-	public void headers() throws Exception {
+	public void httpHeaders() throws Exception {
+		HttpHeaders headers = new HttpHeaders();
+		headers.setAllow(new LinkedHashSet<>(Arrays.asList(HttpMethod.GET, HttpMethod.POST, HttpMethod.OPTIONS)));
+		MethodParameter returnType = on(TestController.class).resolveReturnType(entity(Void.class));
+		HandlerResult result = handlerResult(headers, returnType);
+		MockServerWebExchange exchange = get("/path").toExchange();
+		this.resultHandler.handleResult(exchange, result).block(Duration.ofSeconds(5));
+
+		assertEquals(HttpStatus.OK, exchange.getResponse().getStatusCode());
+		assertEquals(1, exchange.getResponse().getHeaders().size());
+		assertEquals("GET,POST,OPTIONS", exchange.getResponse().getHeaders().getFirst("Allow"));
+		assertResponseBodyIsEmpty(exchange);
+	}
+
+	@Test
+	public void responseEntityHeaders() throws Exception {
 		URI location = new URI("/path");
 		ResponseEntity<Void> value = ResponseEntity.created(location).build();
 		MethodParameter returnType = on(TestController.class).resolveReturnType(entity(Void.class));
@@ -382,6 +402,8 @@ public class ResponseEntityResultHandlerTests {
 
 		ResponseEntity<Void> responseEntityVoid() { return null; }
 
+		HttpHeaders httpHeaders() { return null; }
+
 		Mono<ResponseEntity<String>> mono() { return null; }
 
 		Single<ResponseEntity<String>> single() { return null; }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.