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/*
* Copyright 2002-2016 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.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.messaging.simp.annotation.support;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.core.MethodParameter;
import org.springframework.messaging.Message;
import org.springframework.messaging.MessageHeaders;
import org.springframework.messaging.core.MessageSendingOperations;
import org.springframework.messaging.handler.annotation.SendTo;
import org.springframework.messaging.handler.invocation.HandlerMethodReturnValueHandler;
import org.springframework.messaging.simp.SimpMessageHeaderAccessor;
import org.springframework.messaging.simp.SimpMessageType;
import org.springframework.messaging.simp.SimpMessagingTemplate;
import org.springframework.messaging.simp.annotation.SendToUser;
import org.springframework.messaging.simp.annotation.SubscribeMapping;
import org.springframework.messaging.support.MessageHeaderInitializer;
import org.springframework.util.Assert;
/**
* {@code HandlerMethodReturnValueHandler} for replying directly to a
* subscription. It is supported on methods annotated with
* {@link org.springframework.messaging.simp.annotation.SubscribeMapping
* SubscribeMapping} such that the return value is treated as a response to be
* sent directly back on the session. This allows a client to implement
* a request-response pattern and use it for example to obtain some data upon
* initialization.
*
* <p>The value returned from the method is converted and turned into a
* {@link Message} that is then enriched with the sessionId, subscriptionId, and
* destination of the input message.
*
* <p><strong>Note:</strong> this default behavior for interpreting the return
* value from an {@code @SubscribeMapping} method can be overridden through use
* of the {@link SendTo} or {@link SendToUser} annotations in which case a
* message is prepared and sent to the broker instead.
*
* @author Rossen Stoyanchev
* @author Sebastien Deleuze
* @since 4.0
*/
public class SubscriptionMethodReturnValueHandler implements HandlerMethodReturnValueHandler {
private static final Log logger = LogFactory.getLog(SubscriptionMethodReturnValueHandler.class);
private final MessageSendingOperations<String> messagingTemplate;
private MessageHeaderInitializer headerInitializer;
/**
* Construct a new SubscriptionMethodReturnValueHandler.
* @param template a messaging template to send messages to,
* most likely the "clientOutboundChannel" (must not be {@code null})
*/
public SubscriptionMethodReturnValueHandler(MessageSendingOperations<String> template) {
Assert.notNull(template, "messagingTemplate must not be null");
this.messagingTemplate = template;
}
/**
* Configure a {@link MessageHeaderInitializer} to apply to the headers of all
* messages sent to the client outbound channel.
* <p>By default this property is not set.
*/
public void setHeaderInitializer(MessageHeaderInitializer headerInitializer) {
this.headerInitializer = headerInitializer;
}
/**
* Return the configured header initializer.
*/
public MessageHeaderInitializer getHeaderInitializer() {
return this.headerInitializer;
}
@Override
public boolean supportsReturnType(MethodParameter returnType) {
return (returnType.hasMethodAnnotation(SubscribeMapping.class) &&
!returnType.hasMethodAnnotation(SendTo.class) &&
!returnType.hasMethodAnnotation(SendToUser.class));
}
@Override
public void handleReturnValue(Object returnValue, MethodParameter returnType, Message<?> message)
throws Exception {
if (returnValue == null) {
return;
}
MessageHeaders headers = message.getHeaders();
String destination = SimpMessageHeaderAccessor.getDestination(headers);
String sessionId = SimpMessageHeaderAccessor.getSessionId(headers);
String subscriptionId = SimpMessageHeaderAccessor.getSubscriptionId(headers);
if (subscriptionId == null) {
throw new IllegalStateException("No subscriptionId in " + message +
" returned by: " + returnType.getMethod());
}
if (logger.isDebugEnabled()) {
logger.debug("Reply to @SubscribeMapping: " + returnValue);
}
MessageHeaders headersToSend = createHeaders(sessionId, subscriptionId, returnType);
this.messagingTemplate.convertAndSend(destination, returnValue, headersToSend);
}
private MessageHeaders createHeaders(String sessionId, String subscriptionId, MethodParameter returnType) {
SimpMessageHeaderAccessor accessor = SimpMessageHeaderAccessor.create(SimpMessageType.MESSAGE);
if (getHeaderInitializer() != null) {
getHeaderInitializer().initHeaders(accessor);
}
accessor.setSessionId(sessionId);
accessor.setSubscriptionId(subscriptionId);
accessor.setHeader(SimpMessagingTemplate.CONVERSION_HINT_HEADER, returnType);
accessor.setLeaveMutable(true);
return accessor.getMessageHeaders();
}
}
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