001/*
002 * Copyright 2002-2017 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.messaging.simp.annotation.support;
018
019import org.apache.commons.logging.Log;
020import org.apache.commons.logging.LogFactory;
021
022import org.springframework.core.MethodParameter;
023import org.springframework.messaging.Message;
024import org.springframework.messaging.MessageHeaders;
025import org.springframework.messaging.core.MessageSendingOperations;
026import org.springframework.messaging.handler.annotation.SendTo;
027import org.springframework.messaging.handler.invocation.HandlerMethodReturnValueHandler;
028import org.springframework.messaging.simp.SimpMessageHeaderAccessor;
029import org.springframework.messaging.simp.SimpMessageType;
030import org.springframework.messaging.simp.SimpMessagingTemplate;
031import org.springframework.messaging.simp.annotation.SendToUser;
032import org.springframework.messaging.simp.annotation.SubscribeMapping;
033import org.springframework.messaging.support.MessageHeaderInitializer;
034import org.springframework.util.Assert;
035
036/**
037 * {@code HandlerMethodReturnValueHandler} for replying directly to a
038 * subscription. It is supported on methods annotated with
039 * {@link org.springframework.messaging.simp.annotation.SubscribeMapping
040 * SubscribeMapping} such that the return value is treated as a response to be
041 * sent directly back on the session. This allows a client to implement
042 * a request-response pattern and use it for example to obtain some data upon
043 * initialization.
044 *
045 * <p>The value returned from the method is converted and turned into a
046 * {@link Message} that is then enriched with the sessionId, subscriptionId, and
047 * destination of the input message.
048 *
049 * <p><strong>Note:</strong> this default behavior for interpreting the return
050 * value from an {@code @SubscribeMapping} method can be overridden through use
051 * of the {@link SendTo} or {@link SendToUser} annotations in which case a
052 * message is prepared and sent to the broker instead.
053 *
054 * @author Rossen Stoyanchev
055 * @author Sebastien Deleuze
056 * @since 4.0
057 */
058public class SubscriptionMethodReturnValueHandler implements HandlerMethodReturnValueHandler {
059
060        private static final Log logger = LogFactory.getLog(SubscriptionMethodReturnValueHandler.class);
061
062
063        private final MessageSendingOperations<String> messagingTemplate;
064
065        private MessageHeaderInitializer headerInitializer;
066
067
068        /**
069         * Construct a new SubscriptionMethodReturnValueHandler.
070         * @param template a messaging template to send messages to,
071         * most likely the "clientOutboundChannel" (must not be {@code null})
072         */
073        public SubscriptionMethodReturnValueHandler(MessageSendingOperations<String> template) {
074                Assert.notNull(template, "messagingTemplate must not be null");
075                this.messagingTemplate = template;
076        }
077
078
079        /**
080         * Configure a {@link MessageHeaderInitializer} to apply to the headers of all
081         * messages sent to the client outbound channel.
082         * <p>By default this property is not set.
083         */
084        public void setHeaderInitializer(MessageHeaderInitializer headerInitializer) {
085                this.headerInitializer = headerInitializer;
086        }
087
088        /**
089         * Return the configured header initializer.
090         */
091        public MessageHeaderInitializer getHeaderInitializer() {
092                return this.headerInitializer;
093        }
094
095
096        @Override
097        public boolean supportsReturnType(MethodParameter returnType) {
098                return (returnType.hasMethodAnnotation(SubscribeMapping.class) &&
099                                !returnType.hasMethodAnnotation(SendTo.class) &&
100                                !returnType.hasMethodAnnotation(SendToUser.class));
101        }
102
103        @Override
104        public void handleReturnValue(Object returnValue, MethodParameter returnType, Message<?> message)
105                        throws Exception {
106
107                if (returnValue == null) {
108                        return;
109                }
110
111                MessageHeaders headers = message.getHeaders();
112                String sessionId = SimpMessageHeaderAccessor.getSessionId(headers);
113                String subscriptionId = SimpMessageHeaderAccessor.getSubscriptionId(headers);
114                String destination = SimpMessageHeaderAccessor.getDestination(headers);
115
116                if (subscriptionId == null) {
117                        throw new IllegalStateException("No subscription id in " + message +
118                                        " returned by: " + returnType.getMethod());
119                }
120
121                if (logger.isDebugEnabled()) {
122                        logger.debug("Reply to @SubscribeMapping: " + returnValue);
123                }
124                MessageHeaders headersToSend = createHeaders(sessionId, subscriptionId, returnType);
125                this.messagingTemplate.convertAndSend(destination, returnValue, headersToSend);
126        }
127
128        private MessageHeaders createHeaders(String sessionId, String subscriptionId, MethodParameter returnType) {
129                SimpMessageHeaderAccessor accessor = SimpMessageHeaderAccessor.create(SimpMessageType.MESSAGE);
130                if (getHeaderInitializer() != null) {
131                        getHeaderInitializer().initHeaders(accessor);
132                }
133                accessor.setSessionId(sessionId);
134                accessor.setSubscriptionId(subscriptionId);
135                accessor.setHeader(SimpMessagingTemplate.CONVERSION_HINT_HEADER, returnType);
136                accessor.setLeaveMutable(true);
137                return accessor.getMessageHeaders();
138        }
139
140}