Improve WebFlux exception logging

This commit updates HttpWebHandlerAdapter and
ResponseStatusExceptionHandler in order to specify the method/uri in the
logged message.

It also logs a WARN message for bad request (400) HTTP responses in
order to get some logs when an exception is thrown due to client error
(unable to deserialize request body for example).

Issue: SPR-16447

Author: sdeleuze

spring-web/src/main/java/org/springframework/web/server/adapter/HttpWebHandlerAdapter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -182,7 +182,7 @@ public ApplicationContext getApplicationContext() {
 	public Mono<Void> handle(ServerHttpRequest request, ServerHttpResponse response) {
 		ServerWebExchange exchange = createExchange(request, response);
 		return getDelegate().handle(exchange)
-				.onErrorResume(ex -> handleFailure(response, ex))
+				.onErrorResume(ex -> handleFailure(request, response, ex))
 				.then(Mono.defer(response::setComplete));
 	}
 
@@ -191,7 +191,7 @@ protected ServerWebExchange createExchange(ServerHttpRequest request, ServerHttp
 				getCodecConfigurer(), getLocaleContextResolver(), this.applicationContext);
 	}
 
-	private Mono<Void> handleFailure(ServerHttpResponse response, Throwable ex) {
+	private Mono<Void> handleFailure(ServerHttpRequest request, ServerHttpResponse response, Throwable ex) {
 		if (isDisconnectedClientError(ex)) {
 			if (disconnectedClientLogger.isTraceEnabled()) {
 				disconnectedClientLogger.trace("Looks like the client has gone away", ex);
@@ -204,7 +204,8 @@ else if (disconnectedClientLogger.isDebugEnabled()) {
 			return Mono.empty();
 		}
 		if (response.setStatusCode(HttpStatus.INTERNAL_SERVER_ERROR)) {
-			logger.error("Failed to handle request", ex);
+			logger.error("Failed to handle request [" + request.getMethod() + " "
+					+ request.getURI() + "]", ex);
 			return Mono.empty();
 		}
 		// After the response is committed, propagate errors to the server..

spring-web/src/main/java/org/springframework/web/server/handler/ResponseStatusExceptionHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,6 +21,7 @@
 import reactor.core.publisher.Mono;
 
 import org.springframework.http.HttpStatus;
+import org.springframework.http.server.reactive.ServerHttpRequest;
 import org.springframework.web.server.ResponseStatusException;
 import org.springframework.web.server.ServerWebExchange;
 import org.springframework.web.server.WebExceptionHandler;
@@ -42,11 +43,24 @@ public Mono<Void> handle(ServerWebExchange exchange, Throwable ex) {
 		if (ex instanceof ResponseStatusException) {
 			HttpStatus status = ((ResponseStatusException) ex).getStatus();
 			if (exchange.getResponse().setStatusCode(status)) {
-				logger.trace(ex.getMessage());
+				if (status.is5xxServerError()) {
+					logger.error(buildMessage(exchange.getRequest(), ex));
+				}
+				else if (status == HttpStatus.BAD_REQUEST) {
+					logger.warn(buildMessage(exchange.getRequest(), ex));
+				}
+				else {
+					logger.trace(buildMessage(exchange.getRequest(), ex));
+				}
 				return exchange.getResponse().setComplete();
 			}
 		}
 		return Mono.error(ex);
 	}
 
+	private String buildMessage(ServerHttpRequest request, Throwable ex) {
+		return "Failed to handle request [" + request.getMethod() + " "
+				+ request.getURI() + "]: " + ex.getMessage();
+	}
+
 }