Merge pull request #11909 from sdeleuze:improved-error-logging

* pr/11909:
  Polish
  Improve WebFlux error logging

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

@@ -39,6 +39,7 @@ import org.springframework.web.reactive.function.server.RouterFunction;
 import org.springframework.web.reactive.function.server.RouterFunctions;
 import org.springframework.web.reactive.function.server.ServerRequest;
 import org.springframework.web.reactive.function.server.ServerResponse;
+import org.springframework.web.server.ResponseStatusException;
 
 /**
  * Basic global {@link org.springframework.web.server.WebExceptionHandler}, rendering
@@ -188,16 +189,43 @@ public class DefaultErrorWebExceptionHandler extends AbstractErrorWebExceptionHa
 	}
 
 	/**
-	 * Log the original exception if handling it results in a Server Error.
+	 * Log the original exception if handling it results in a Server Error or a Bad Request
+	 * (Client Error with 400 status code) one.
 	 * @param request the source request
 	 * @param errorStatus the HTTP error status
 	 */
 	protected void logError(ServerRequest request, HttpStatus errorStatus) {
 		if (errorStatus.is5xxServerError()) {
 			Throwable ex = getError(request);
-			logger.error("Failed to handle request [" + request.methodName() + " "
-					+ request.uri() + "]", ex);
+			if (ex instanceof ResponseStatusException) {
+				logger.error(buildMessage(request, ex));
+			}
+			else {
+				logger.error(buildMessage(request, null), ex);
+			}
+		}
+		else if (errorStatus == HttpStatus.BAD_REQUEST) {
+			Throwable ex = getError(request);
+			if (ex instanceof ResponseStatusException) {
+				logger.warn(buildMessage(request, ex));
+			}
+			else {
+				logger.warn(buildMessage(request, null), ex);
+			}
 		}
 	}
 
+	private String buildMessage(ServerRequest request, Throwable ex) {
+		StringBuilder message = new StringBuilder("Failed to handle request [");
+		message.append(request.methodName());
+		message.append(" ");
+		message.append(request.uri());
+		message.append("]");
+		if (ex != null) {
+			message.append(": ");
+			message.append(ex.getMessage());
+		}
+		return message.toString();
+	}
+
 }

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

@@ -131,6 +131,9 @@ public class DefaultErrorWebExceptionHandlerIntegrationTests {
 					.isEqualTo(("/bind")).jsonPath("exception").doesNotExist()
 					.jsonPath("errors").isArray().jsonPath("message").isNotEmpty();
 		});
+		this.output.expect(allOf(containsString("Failed to handle request [POST /bind]"),
+				containsString("Validation failed for argument"),
+				containsString("Field error in object 'dummyBody' on field 'content'")));
 	}
 
 	@Test