001/*
002 * Copyright 2002-2018 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 java.util.ArrayList;
020import java.util.Collections;
021import java.util.List;
022
023import org.apache.commons.logging.Log;
024import org.apache.commons.logging.LogFactory;
025
026import org.springframework.core.MethodParameter;
027import org.springframework.lang.Nullable;
028import org.springframework.web.context.request.NativeWebRequest;
029
030/**
031 * Handles method return values by delegating to a list of registered {@link HandlerMethodReturnValueHandler HandlerMethodReturnValueHandlers}.
032 * Previously resolved return types are cached for faster lookups.
033 *
034 * @author Rossen Stoyanchev
035 * @since 3.1
036 */
037public class HandlerMethodReturnValueHandlerComposite implements HandlerMethodReturnValueHandler {
038
039        protected final Log logger = LogFactory.getLog(getClass());
040
041        private final List<HandlerMethodReturnValueHandler> returnValueHandlers = new ArrayList<>();
042
043
044        /**
045         * Return a read-only list with the registered handlers, or an empty list.
046         */
047        public List<HandlerMethodReturnValueHandler> getHandlers() {
048                return Collections.unmodifiableList(this.returnValueHandlers);
049        }
050
051        /**
052         * Whether the given {@linkplain MethodParameter method return type} is supported by any registered
053         * {@link HandlerMethodReturnValueHandler}.
054         */
055        @Override
056        public boolean supportsReturnType(MethodParameter returnType) {
057                return getReturnValueHandler(returnType) != null;
058        }
059
060        @Nullable
061        private HandlerMethodReturnValueHandler getReturnValueHandler(MethodParameter returnType) {
062                for (HandlerMethodReturnValueHandler handler : this.returnValueHandlers) {
063                        if (handler.supportsReturnType(returnType)) {
064                                return handler;
065                        }
066                }
067                return null;
068        }
069
070        /**
071         * Iterate over registered {@link HandlerMethodReturnValueHandler HandlerMethodReturnValueHandlers} and invoke the one that supports it.
072         * @throws IllegalStateException if no suitable {@link HandlerMethodReturnValueHandler} is found.
073         */
074        @Override
075        public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
076                        ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
077
078                HandlerMethodReturnValueHandler handler = selectHandler(returnValue, returnType);
079                if (handler == null) {
080                        throw new IllegalArgumentException("Unknown return value type: " + returnType.getParameterType().getName());
081                }
082                handler.handleReturnValue(returnValue, returnType, mavContainer, webRequest);
083        }
084
085        @Nullable
086        private HandlerMethodReturnValueHandler selectHandler(@Nullable Object value, MethodParameter returnType) {
087                boolean isAsyncValue = isAsyncReturnValue(value, returnType);
088                for (HandlerMethodReturnValueHandler handler : this.returnValueHandlers) {
089                        if (isAsyncValue && !(handler instanceof AsyncHandlerMethodReturnValueHandler)) {
090                                continue;
091                        }
092                        if (handler.supportsReturnType(returnType)) {
093                                return handler;
094                        }
095                }
096                return null;
097        }
098
099        private boolean isAsyncReturnValue(@Nullable Object value, MethodParameter returnType) {
100                for (HandlerMethodReturnValueHandler handler : this.returnValueHandlers) {
101                        if (handler instanceof AsyncHandlerMethodReturnValueHandler &&
102                                        ((AsyncHandlerMethodReturnValueHandler) handler).isAsyncReturnValue(value, returnType)) {
103                                return true;
104                        }
105                }
106                return false;
107        }
108
109        /**
110         * Add the given {@link HandlerMethodReturnValueHandler}.
111         */
112        public HandlerMethodReturnValueHandlerComposite addHandler(HandlerMethodReturnValueHandler handler) {
113                this.returnValueHandlers.add(handler);
114                return this;
115        }
116
117        /**
118         * Add the given {@link HandlerMethodReturnValueHandler HandlerMethodReturnValueHandlers}.
119         */
120        public HandlerMethodReturnValueHandlerComposite addHandlers(
121                        @Nullable List<? extends HandlerMethodReturnValueHandler> handlers) {
122
123                if (handlers != null) {
124                        this.returnValueHandlers.addAll(handlers);
125                }
126                return this;
127        }
128
129}