ResponseStatusException reason as problem detail should be updated vi…

…a MessageSource

Closes GH-30222

spring-web/src/main/java/org/springframework/web/ErrorResponse.java

@@ -40,6 +40,7 @@
  * {@code @RestController} or {@code RestControllerAdvice} class.
  *
  * @author Rossen Stoyanchev
+ * @author Yanming Zhou
  * @since 6.0
  * @see ErrorResponseException
  */
@@ -124,6 +125,14 @@ default ProblemDetail updateAndGetBody(@Nullable MessageSource messageSource, Lo
 			if (detail != null) {
 				getBody().setDetail(detail);
 			}
+			else {
+				// detail from ResponseStatusException reason may be message code
+				detail = getBody().getDetail();
+				if (detail != null) {
+					detail = messageSource.getMessage(detail, null, detail, locale);
+					getBody().setDetail(detail);
+				}
+			}
 			String title = messageSource.getMessage(getTitleMessageCode(), null, null, locale);
 			if (title != null) {
 				getBody().setTitle(title);

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

@@ -58,6 +58,7 @@
 import org.springframework.web.context.request.async.AsyncRequestTimeoutException;
 import org.springframework.web.context.support.StaticWebApplicationContext;
 import org.springframework.web.multipart.support.MissingServletRequestPartException;
+import org.springframework.web.server.ResponseStatusException;
 import org.springframework.web.servlet.DispatcherServlet;
 import org.springframework.web.servlet.ModelAndView;
 import org.springframework.web.servlet.NoHandlerFoundException;
@@ -72,6 +73,7 @@
  * Unit tests for {@link ResponseEntityExceptionHandler}.
  *
  * @author Rossen Stoyanchev
+ * @author Yanming Zhou
  */
 public class ResponseEntityExceptionHandlerTests {
 
@@ -189,6 +191,30 @@ public void errorResponseProblemDetailViaMessageSource() {
 		}
 	}
 
+	@Test
+	public void reasonAsDetailShouldBeUpdatedViaMessageSource() {
+
+		Locale locale = Locale.UK;
+		LocaleContextHolder.setLocale(locale);
+
+		String code = "bad.request";
+		String message = "Breaking Bad Request";
+		try {
+			StaticMessageSource messageSource = new StaticMessageSource();
+			messageSource.addMessage(code, locale, message);
+
+			this.exceptionHandler.setMessageSource(messageSource);
+
+			ResponseEntity<?> entity = testException(new ResponseStatusException(HttpStatus.BAD_REQUEST, code));
+
+			ProblemDetail body = (ProblemDetail) entity.getBody();
+			assertThat(body.getDetail()).isEqualTo(message);
+		}
+		finally {
+			LocaleContextHolder.resetLocaleContext();
+		}
+	}
+
 	@Test
 	public void conversionNotSupported() {
 		testException(new ConversionNotSupportedException(new Object(), Object.class, null));