Use sendError in ResponseStatusExceptionResolver

Prior to this commit, the `ResponseStatusExceptionResolver` would use:
* `HttpServletResponse.sendError` if both a status and a reason are set
on the `@ResponseStatus` annotation
* `HttpServletResponse.setStatus` if only a status is set on the
`@ResponseStatus` annotation

This is actually a change of behavior, since this Resolver was using
`sendError` in all cases previously.

Because this change can create issues such as
https://github.com/spring-projects/spring-boot/issues/3623
this commit rollbacks those changes and clarifies the behavior on the
javadoc of the annotation itself.

Issue: SPR-11193, SPR-13226

spring-web/src/main/java/org/springframework/web/bind/annotation/ResponseStatus.java

@@ -30,11 +30,23 @@ import org.springframework.http.HttpStatus;
  * {@link #reason} that should be returned.
  *
  * <p>The status code is applied to the HTTP response when the handler
- * method is invoked, or whenever said exception is thrown.
+ * method is invoked.
+ *
+ * <p><strong>Note:</strong> when using this annotation on an exception class,
+ * or when setting the {@code reason} attribute of the annotation,
+ * the {@code HttpServletResponse.sendError} method will be used.
+ *
+ * With {@code HttpServletResponse.sendError}, the response is considered
+ * complete and should not be written to any further.
+ * Furthermore servlet container will typically write an HTML error page
+ * therefore making the use of a reason unsuitable for REST APIs.
+ * For such cases prefer the use of {@link org.springframework.http.ResponseEntity}
+ * as a return type and avoid {@code ResponseStatus} altogether.
  *
  * @author Arjen Poutsma
  * @author Sam Brannen
  * @see org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver
+ * @see javax.servlet.http.HttpServletResponse#sendError(int, String)
  * @since 3.0
  */
 @Target({ElementType.TYPE, ElementType.METHOD})
@@ -54,18 +66,13 @@ public @interface ResponseStatus {
 	 * typically be changed to something more appropriate.
 	 * @since 4.2
 	 * @see javax.servlet.http.HttpServletResponse#setStatus(int)
+	 * @see javax.servlet.http.HttpServletResponse#sendError(int)
 	 */
 	@AliasFor("value")
 	HttpStatus code() default HttpStatus.INTERNAL_SERVER_ERROR;
 
 	/**
 	 * The <em>reason</em> to be used for the response.
-	 * <p><strong>Note:</strong> due to the use of
-	 * {@code HttpServletResponse.sendError(int, String)}, the response will be
-	 * considered complete and should not be written to any further. Furthermore
-	 * servlet container will typically write an HTML error page therefore making
-	 * the use of a reason unsuitable for REST APIs. For such cases prefer
-	 * sending error details in the body of the response.
 	 * @see javax.servlet.http.HttpServletResponse#sendError(int, String)
 	 */
 	String reason() default "";

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

@@ -100,7 +100,7 @@ public class ResponseStatusExceptionResolver extends AbstractHandlerExceptionRes
 			reason = this.messageSource.getMessage(reason, null, reason, LocaleContextHolder.getLocale());
 		}
 		if (!StringUtils.hasLength(reason)) {
-			response.setStatus(statusCode);
+			response.sendError(statusCode);
 		}
 		else {
 			response.sendError(statusCode, reason);

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

@@ -57,6 +57,7 @@ public class ResponseStatusExceptionResolverTests {
 		assertNotNull("No ModelAndView returned", mav);
 		assertTrue("No Empty ModelAndView returned", mav.isEmpty());
 		assertEquals("Invalid status code", 400, response.getStatus());
+		assertTrue("Response has not been committed", response.isCommitted());
 	}
 
 	@Test
@@ -67,6 +68,7 @@ public class ResponseStatusExceptionResolverTests {
 		assertTrue("No Empty ModelAndView returned", mav.isEmpty());
 		assertEquals("Invalid status code", 410, response.getStatus());
 		assertEquals("Invalid status reason", "You suck!", response.getErrorMessage());
+		assertTrue("Response has not been committed", response.isCommitted());
 	}
 
 	@Test