ResponseStatusException associated headers

A ResponseStatus exception now exposes extra method to return headers
for the response. This is used in ResponseStatusExceptionHandler to
apply the headers to the response.

Closes gh-23741

spring-web/src/main/java/org/springframework/web/server/MethodNotAllowedException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -19,12 +19,15 @@ package org.springframework.web.server;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashSet;
+import java.util.Map;
 import java.util.Set;
 
 import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.CollectionUtils;
+import org.springframework.util.StringUtils;
 
 /**
  * Exception for errors that fit response status 405 (method not allowed).
@@ -37,7 +40,7 @@ public class MethodNotAllowedException extends ResponseStatusException {
 
 	private final String method;
 
-	private final Set<HttpMethod> supportedMethods;
+	private final Set<HttpMethod> httpMethods;
 
 
 	public MethodNotAllowedException(HttpMethod method, Collection<HttpMethod> supportedMethods) {
@@ -51,10 +54,21 @@ public class MethodNotAllowedException extends ResponseStatusException {
 			supportedMethods = Collections.emptySet();
 		}
 		this.method = method;
-		this.supportedMethods = Collections.unmodifiableSet(new HashSet<>(supportedMethods));
+		this.httpMethods = Collections.unmodifiableSet(new HashSet<>(supportedMethods));
 	}
 
 
+	/**
+	 * Return a Map with an "Allow" header.
+	 * @since 5.1.11
+	 */
+	@Override
+	public Map<String, String> getHeaders() {
+		return !CollectionUtils.isEmpty(this.httpMethods) ?
+				Collections.singletonMap("Allow", StringUtils.collectionToDelimitedString(this.httpMethods, ", ")) :
+				Collections.emptyMap();
+	}
+
 	/**
 	 * Return the HTTP method for the failed request.
 	 */
@@ -66,6 +80,7 @@ public class MethodNotAllowedException extends ResponseStatusException {
 	 * Return the list of supported HTTP methods.
 	 */
 	public Set<HttpMethod> getSupportedMethods() {
-		return this.supportedMethods;
+		return this.httpMethods;
 	}
+
 }

spring-web/src/main/java/org/springframework/web/server/NotAcceptableStatusException.java

@@ -18,9 +18,11 @@ package org.springframework.web.server;
 
 import java.util.Collections;
 import java.util.List;
+import java.util.Map;
 
 import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
+import org.springframework.util.CollectionUtils;
 
 /**
  * Exception for errors that fit response status 406 (not acceptable).
@@ -51,6 +53,17 @@ public class NotAcceptableStatusException extends ResponseStatusException {
 	}
 
 
+	/**
+	 * Return a Map with an "Accept" header, or an empty map.
+	 * @since 5.1.11
+	 */
+	@Override
+	public Map<String, String> getHeaders() {
+		return !CollectionUtils.isEmpty(this.supportedMediaTypes) ?
+				Collections.singletonMap("Accept", MediaType.toString(this.supportedMediaTypes)) :
+				Collections.emptyMap();
+	}
+
 	/**
 	 * Return the list of supported content types in cases when the Accept
 	 * header is parsed but not supported, or an empty list otherwise.

spring-web/src/main/java/org/springframework/web/server/ResponseStatusException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -16,6 +16,9 @@
 
 package org.springframework.web.server;
 
+import java.util.Collections;
+import java.util.Map;
+
 import org.springframework.core.NestedExceptionUtils;
 import org.springframework.core.NestedRuntimeException;
 import org.springframework.http.HttpStatus;
@@ -72,12 +75,21 @@ public class ResponseStatusException extends NestedRuntimeException {
 
 
 	/**
-	 * The HTTP status that fits the exception (never {@code null}).
+	 * Return the HTTP status associated with this exception.
 	 */
 	public HttpStatus getStatus() {
 		return this.status;
 	}
 
+	/**
+	 * Return response headers associated with the exception, possibly required
+	 * for the given status code (e.g. "Allow", "Accept").
+	 * @since 5.1.11
+	 */
+	public Map<String, String> getHeaders() {
+		return Collections.emptyMap();
+	}
+
 	/**
 	 * The reason explaining the exception (potentially {@code null} or empty).
 	 */
@@ -86,6 +98,7 @@ public class ResponseStatusException extends NestedRuntimeException {
 		return this.reason;
 	}
 
+
 	@Override
 	public String getMessage() {
 		String msg = this.status + (this.reason != null ? " \"" + this.reason + "\"" : "");

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -22,6 +22,7 @@ import reactor.core.publisher.Mono;
 
 import org.springframework.http.HttpStatus;
 import org.springframework.http.server.reactive.ServerHttpRequest;
+import org.springframework.http.server.reactive.ServerHttpResponse;
 import org.springframework.lang.Nullable;
 import org.springframework.web.server.ResponseStatusException;
 import org.springframework.web.server.ServerWebExchange;
@@ -62,8 +63,7 @@ public class ResponseStatusExceptionHandler implements WebExceptionHandler {
 
 	@Override
 	public Mono<Void> handle(ServerWebExchange exchange, Throwable ex) {
-		HttpStatus status = resolveStatus(ex);
-		if (status == null || !exchange.getResponse().setStatusCode(status)) {
+		if (!updateResponse(exchange.getResponse(), ex)) {
 			return Mono.error(ex);
 		}
 
@@ -86,16 +86,25 @@ public class ResponseStatusExceptionHandler implements WebExceptionHandler {
 		return "Resolved [" + reason + "] for HTTP " + request.getMethod() + " " + path;
 	}
 
-	@Nullable
-	private HttpStatus resolveStatus(Throwable ex) {
+	private boolean updateResponse(ServerHttpResponse response, Throwable ex) {
+		boolean result = false;
 		HttpStatus status = determineStatus(ex);
-		if (status == null) {
-			Throwable cause = ex.getCause();
-			if (cause != null) {
-				status = resolveStatus(cause);
+		if (status != null) {
+			if (response.setStatusCode(status)) {
+				if (ex instanceof ResponseStatusException) {
+					((ResponseStatusException) ex).getHeaders()
+							.forEach((name, value) -> response.getHeaders().add(name, value));
+				}
+				result = true;
 			}
 		}
-		return status;
+		else {
+			Throwable cause = ex.getCause();
+			if (cause != null) {
+				result = updateResponse(response, cause);
+			}
+		}
+		return result;
 	}
 
 	/**