Polish "Set UTF-8 charset for whitelabel HTML error pages"

Closes gh-16611

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

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.autoconfigure.web.reactive.error;
 
+import java.nio.charset.StandardCharsets;
 import java.util.Collections;
 import java.util.EnumMap;
 import java.util.List;
@@ -73,6 +74,9 @@ import static org.springframework.web.reactive.function.server.RouterFunctions.r
  */
 public class DefaultErrorWebExceptionHandler extends AbstractErrorWebExceptionHandler {
 
+	private static final MediaType TEXT_HTML_UTF8 = new MediaType("text", "html",
+			StandardCharsets.UTF_8);
+
 	private static final Map<HttpStatus.Series, String> SERIES_VIEWS;
 
 	static {
@@ -105,8 +109,6 @@ public class DefaultErrorWebExceptionHandler extends AbstractErrorWebExceptionHa
 				this::renderErrorResponse);
 	}
 
-	private static final MediaType HTML_CONTENT_TYPE =  MediaType.valueOf(MediaType.TEXT_HTML_VALUE+";charset=UTF-8");
-
 	/**
 	 * Render the error information as an HTML view.
 	 * @param request the current request
@@ -117,7 +119,7 @@ public class DefaultErrorWebExceptionHandler extends AbstractErrorWebExceptionHa
 		Map<String, Object> error = getErrorAttributes(request, includeStackTrace);
 		HttpStatus errorStatus = getHttpStatus(error);
 		ServerResponse.BodyBuilder responseBody = ServerResponse.status(errorStatus)
-				.contentType(HTML_CONTENT_TYPE);
+				.contentType(TEXT_HTML_UTF8);
 		return Flux
 				.just("error/" + errorStatus.value(),
 						"error/" + SERIES_VIEWS.get(errorStatus.series()), "error/error")

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/error/ErrorMvcAutoConfiguration.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.autoconfigure.web.servlet.error;
 
+import java.nio.charset.StandardCharsets;
 import java.util.Date;
 import java.util.Map;
 import java.util.stream.Collectors;
@@ -66,6 +67,7 @@ import org.springframework.context.annotation.Conditional;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.Ordered;
 import org.springframework.core.type.AnnotatedTypeMetadata;
+import org.springframework.http.MediaType;
 import org.springframework.web.servlet.DispatcherServlet;
 import org.springframework.web.servlet.View;
 import org.springframework.web.servlet.view.BeanNameViewResolver;
@@ -202,6 +204,9 @@ public class ErrorMvcAutoConfiguration {
 	 */
 	private static class StaticView implements View {
 
+		private static final MediaType TEXT_HTML_UTF8 = new MediaType("text", "html",
+				StandardCharsets.UTF_8);
+
 		private static final Log logger = LogFactory.getLog(StaticView.class);
 
 		@Override
@@ -212,6 +217,7 @@ public class ErrorMvcAutoConfiguration {
 				logger.error(message);
 				return;
 			}
+			response.setContentType(TEXT_HTML_UTF8.toString());
 			StringBuilder builder = new StringBuilder();
 			Date timestamp = (Date) model.get("timestamp");
 			Object message = model.get("message");

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

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.autoconfigure.web.reactive.error;
 
+import java.nio.charset.StandardCharsets;
+
 import javax.validation.Valid;
 
 import org.junit.jupiter.api.Test;
@@ -55,6 +57,9 @@ import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
  */
 public class DefaultErrorWebExceptionHandlerIntegrationTests {
 
+	private static final MediaType TEXT_HTML_UTF8 = new MediaType("text", "html",
+			StandardCharsets.UTF_8);
+
 	private final LogIdFilter logIdFilter = new LogIdFilter();
 
 	@RegisterExtension
@@ -106,8 +111,8 @@ public class DefaultErrorWebExceptionHandlerIntegrationTests {
 			WebTestClient client = getWebClient(context);
 			String body = client.get().uri("/").accept(MediaType.TEXT_HTML).exchange()
 					.expectStatus().isEqualTo(HttpStatus.INTERNAL_SERVER_ERROR)
-					.expectHeader().contentType(MediaType.TEXT_HTML)
-					.expectBody(String.class).returnResult().getResponseBody();
+					.expectHeader().contentType(TEXT_HTML_UTF8).expectBody(String.class)
+					.returnResult().getResponseBody();
 			assertThat(body).contains("status: 500").contains("message: Expected!");
 		});
 	}
@@ -201,7 +206,7 @@ public class DefaultErrorWebExceptionHandlerIntegrationTests {
 					String body = client.get().uri("/").accept(MediaType.TEXT_HTML)
 							.exchange().expectStatus()
 							.isEqualTo(HttpStatus.INTERNAL_SERVER_ERROR).expectHeader()
-							.contentType(MediaType.TEXT_HTML).expectBody(String.class)
+							.contentType(TEXT_HTML_UTF8).expectBody(String.class)
 							.returnResult().getResponseBody();
 					assertThat(body).contains("Whitelabel Error Page")
 							.contains(this.logIdFilter.getLogId())
@@ -219,7 +224,7 @@ public class DefaultErrorWebExceptionHandlerIntegrationTests {
 					String body = client.get().uri("/html").accept(MediaType.TEXT_HTML)
 							.exchange().expectStatus()
 							.isEqualTo(HttpStatus.INTERNAL_SERVER_ERROR).expectHeader()
-							.contentType(MediaType.TEXT_HTML).expectBody(String.class)
+							.contentType(TEXT_HTML_UTF8).expectBody(String.class)
 							.returnResult().getResponseBody();
 					assertThat(body).contains("Whitelabel Error Page")
 							.contains(this.logIdFilter.getLogId())
@@ -235,7 +240,7 @@ public class DefaultErrorWebExceptionHandlerIntegrationTests {
 					WebTestClient client = getWebClient(context);
 					String body = client.get().uri("/notfound")
 							.accept(MediaType.TEXT_HTML).exchange().expectStatus()
-							.isNotFound().expectHeader().contentType(MediaType.TEXT_HTML)
+							.isNotFound().expectHeader().contentType(TEXT_HTML_UTF8)
 							.expectBody(String.class).returnResult().getResponseBody();
 					assertThat(body).contains("Whitelabel Error Page")
 							.contains(this.logIdFilter.getLogId())

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/servlet/error/ErrorMvcAutoConfigurationTests.java

@@ -56,6 +56,8 @@ public class ErrorMvcAutoConfigurationTests {
 					new IllegalStateException("Exception message"), false);
 			errorView.render(errorAttributes.getErrorAttributes(webRequest, true),
 					webRequest.getRequest(), webRequest.getResponse());
+			assertThat(webRequest.getResponse().getContentType())
+					.isEqualTo("text/html;charset=UTF-8");
 			String responseString = ((MockHttpServletResponse) webRequest.getResponse())
 					.getContentAsString();
 			assertThat(responseString).contains(