From 7be3a61a14eb8bce18bfce091b51961666d8e7a7 Mon Sep 17 00:00:00 2001
From: Brian Clozel <brian.clozel@broadcom.com>
Date: Tue, 22 Sep 2026 16:56:40 +0200
Subject: [PATCH] ResponseStatusException should not override custom reason

Prior to this commit, `ResponseStatusException` would resolve the
"detail" part of a problem detail response from message codes only
(default or custom ones). If the `reason` given as an argument to the
exception was a custom message, it would be overwritten in the process.

This commit ensures that we use custom reason messages when they don't
resolve as message codes.

Fixes gh-36984
---
 .../web/server/ResponseStatusException.java   | 27 +++++++++++--------
 .../web/ErrorResponseExceptionTests.java      | 22 +++++++++++++++
 2 files changed, 38 insertions(+), 11 deletions(-)

diff --git a/spring-web/src/main/java/org/springframework/web/server/ResponseStatusException.java b/spring-web/src/main/java/org/springframework/web/server/ResponseStatusException.java
index 01f5bdfd3f4..9996c24900f 100644
--- a/spring-web/src/main/java/org/springframework/web/server/ResponseStatusException.java
+++ b/spring-web/src/main/java/org/springframework/web/server/ResponseStatusException.java
@@ -17,6 +17,7 @@
 package org.springframework.web.server;
 
 import java.util.Locale;
+import java.util.Objects;
 
 import org.jspecify.annotations.Nullable;
 
@@ -117,19 +118,23 @@ public class ResponseStatusException extends ErrorResponseException {
 
 	@Override
 	public ProblemDetail updateAndGetBody(@Nullable MessageSource messageSource, Locale locale) {
-		super.updateAndGetBody(messageSource, locale);
-
-		// The reason may be a code (consistent with ResponseStatusExceptionResolver)
-
-		if (messageSource != null && getReason() != null && getReason().equals(getBody().getDetail())) {
-			Object[] arguments = getDetailMessageArguments(messageSource, locale);
-			String resolved = messageSource.getMessage(getReason(), arguments, null, locale);
-			if (resolved != null) {
-				getBody().setDetail(resolved);
+		String reason = getReason();
+		if (reason != null) {
+			boolean detailNotCustomized = reason.equals(getBody().getDetail());
+			super.updateAndGetBody(messageSource, locale);
+			if (!detailNotCustomized) {
+				return getBody();
 			}
+			// The reason may itself be a code (consistent with ResponseStatusExceptionResolver)
+			String resolved = null;
+			if (messageSource != null) {
+				resolved = messageSource.getMessage(reason, getDetailMessageArguments(messageSource, locale), null, locale);
+			}
+			// set to the custom reason if no message was resolved
+			getBody().setDetail(Objects.requireNonNullElse(resolved, reason));
+			return getBody();
 		}
-
-		return getBody();
+		return super.updateAndGetBody(messageSource, locale);
 	}
 
 	@Override
diff --git a/spring-web/src/test/java/org/springframework/web/ErrorResponseExceptionTests.java b/spring-web/src/test/java/org/springframework/web/ErrorResponseExceptionTests.java
index 6c90e76e62c..3b8fa068c35 100644
--- a/spring-web/src/test/java/org/springframework/web/ErrorResponseExceptionTests.java
+++ b/spring-web/src/test/java/org/springframework/web/ErrorResponseExceptionTests.java
@@ -424,6 +424,28 @@ class ErrorResponseExceptionTests {
 		}
 	}
 
+	@Test  // gh-36984
+	void responseStatusExceptionCustomReason() {
+		Locale locale = Locale.UK;
+		LocaleContextHolder.setLocale(locale);
+
+		try {
+			String reason = "bad.request";
+			String message = "Breaking Bad Request";
+			StaticMessageSource messageSource = new StaticMessageSource();
+			messageSource.addMessage(reason, locale, message);
+
+			String customReason = "my custom reason";
+			ResponseStatusException ex = new ResponseStatusException(HttpStatus.BAD_REQUEST, customReason);
+
+			ProblemDetail problemDetail = ex.updateAndGetBody(messageSource, locale);
+			assertThat(problemDetail.getDetail()).isEqualTo(customReason);
+		}
+		finally {
+			LocaleContextHolder.resetLocaleContext();
+		}
+	}
+
 	private void assertStatus(ErrorResponse ex, HttpStatus status) {
 		ProblemDetail body = ex.getBody();
 		assertThat(ex.getStatusCode()).isEqualTo(status);