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}