001/* 002 * Copyright 2002-2019 the original author or authors. 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * https://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package org.springframework.web.method.support; 018 019import org.springframework.core.MethodParameter; 020import org.springframework.lang.Nullable; 021 022/** 023 * A return value handler that supports async types. Such return value types 024 * need to be handled with priority so the async value can be "unwrapped". 025 * 026 * <p><strong>Note: </strong> implementing this contract is not required but it 027 * should be implemented when the handler needs to be prioritized ahead of others. 028 * For example custom (async) handlers, by default ordered after built-in 029 * handlers, should take precedence over {@code @ResponseBody} or 030 * {@code @ModelAttribute} handling, which should occur once the async value is 031 * ready. By contrast, built-in (async) handlers are already ordered ahead of 032 * sync handlers. 033 * 034 * @author Rossen Stoyanchev 035 * @since 4.2 036 */ 037public interface AsyncHandlerMethodReturnValueHandler extends HandlerMethodReturnValueHandler { 038 039 /** 040 * Whether the given return value represents asynchronous computation. 041 * @param returnValue the value returned from the handler method 042 * @param returnType the return type 043 * @return {@code true} if the return value type represents an async value 044 */ 045 boolean isAsyncReturnValue(@Nullable Object returnValue, MethodParameter returnType); 046 047}