Add support for @ResponseStatus in DefaultErrorAttributes

This commit adds support for @ResponseStatus in DefaultErrorAttributes
mimicking the semantics of @ResponseStatus in SpringMVC.

Throwables annotated with @ResponseStatus handled by
DefaultErrorAttributes will result in the following error attributes:
* 'status' set as the return value of the HttpStatus#value()
  defined as @ResponseStatus#value()
* 'error' set to the default reason phrase of the HttpStatus
  defined as @ResponseStatus#value()
* 'message' defined as the value of @ResponseStatus#reason(),
  or the default HttpStatus's reason phrase if left unspecified

See gh-14744

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/reactive/error/DefaultErrorAttributes.java

@@ -22,9 +22,11 @@ import java.util.Date;
 import java.util.LinkedHashMap;
 import java.util.Map;
 
+import org.springframework.core.annotation.AnnotatedElementUtils;
 import org.springframework.http.HttpStatus;
 import org.springframework.validation.BindingResult;
 import org.springframework.validation.ObjectError;
+import org.springframework.web.bind.annotation.ResponseStatus;
 import org.springframework.web.bind.support.WebExchangeBindException;
 import org.springframework.web.reactive.function.server.ServerRequest;
 import org.springframework.web.server.ResponseStatusException;
@@ -46,6 +48,7 @@ import org.springframework.web.server.ServerWebExchange;
  *
  * @author Brian Clozel
  * @author Stephane Nicoll
+ * @author Michele Mancioppi
  * @since 2.0.0
  * @see ErrorAttributes
  */
@@ -91,6 +94,14 @@ public class DefaultErrorAttributes implements ErrorAttributes {
 		if (error instanceof ResponseStatusException) {
 			return ((ResponseStatusException) error).getStatus();
 		}
+
+		ResponseStatus responseStatus = AnnotatedElementUtils
+				.findMergedAnnotation(error.getClass(), ResponseStatus.class);
+
+		if (responseStatus != null) {
+			return responseStatus.code();
+		}
+
 		return HttpStatus.INTERNAL_SERVER_ERROR;
 	}
 
@@ -98,9 +109,18 @@ public class DefaultErrorAttributes implements ErrorAttributes {
 		if (error instanceof WebExchangeBindException) {
 			return error.getMessage();
 		}
+
 		if (error instanceof ResponseStatusException) {
 			return ((ResponseStatusException) error).getReason();
 		}
+
+		ResponseStatus responseStatus = AnnotatedElementUtils
+				.findMergedAnnotation(error.getClass(), ResponseStatus.class);
+
+		if (responseStatus != null) {
+			return responseStatus.reason();
+		}
+
 		return error.getMessage();
 	}
 

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/reactive/error/DefaultErrorAttributesTests.java

@@ -35,6 +35,7 @@ import org.springframework.mock.web.server.MockServerWebExchange;
 import org.springframework.validation.BindingResult;
 import org.springframework.validation.MapBindingResult;
 import org.springframework.validation.ObjectError;
+import org.springframework.web.bind.annotation.ResponseStatus;
 import org.springframework.web.bind.support.WebExchangeBindException;
 import org.springframework.web.reactive.function.server.ServerRequest;
 import org.springframework.web.server.ResponseStatusException;
@@ -90,6 +91,29 @@ public class DefaultErrorAttributesTests {
 		assertThat(attributes.get("status")).isEqualTo(500);
 	}
 
+	@Test
+	public void annotatedResponseStatusCode() {
+		Exception error = new CustomException();
+		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
+		Map<String, Object> attributes = this.errorAttributes
+				.getErrorAttributes(buildServerRequest(request, error), false);
+		assertThat(attributes.get("error"))
+				.isEqualTo(HttpStatus.I_AM_A_TEAPOT.getReasonPhrase());
+		assertThat(attributes.get("status")).isEqualTo(HttpStatus.I_AM_A_TEAPOT.value());
+	}
+
+	@Test
+	public void annotatedResponseStatusCodeWithCustomReasonPhrase() {
+		Exception error = new Custom2Exception();
+		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
+		Map<String, Object> attributes = this.errorAttributes
+				.getErrorAttributes(buildServerRequest(request, error), false);
+		assertThat(attributes.get("error"))
+				.isEqualTo(HttpStatus.I_AM_A_TEAPOT.getReasonPhrase());
+		assertThat(attributes.get("status")).isEqualTo(HttpStatus.I_AM_A_TEAPOT.value());
+		assertThat(attributes.get("message")).isEqualTo("Nope!");
+	}
+
 	@Test
 	public void includeStatusCode() {
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
@@ -214,4 +238,14 @@ public class DefaultErrorAttributesTests {
 		return 42;
 	}
 
+	@ResponseStatus(HttpStatus.I_AM_A_TEAPOT)
+	private static class CustomException extends RuntimeException {
+
+	}
+
+	@ResponseStatus(value = HttpStatus.I_AM_A_TEAPOT, reason = "Nope!")
+	private static class Custom2Exception extends RuntimeException {
+
+	}
+
 }