messagebased RPC with topic - spring

Question

A simple message-based RPC is very easy to create. The server side exports the service, the client side uses a proxy.
What is the best way, to make the same thing with multiple repliers?
I want to send a request from a client. Then the client waits while all (maybe with timeout) replies are received.

Answer 1

You could use an aggregator with appropriate correlation and release strategies (and a group timeout).
EDIT:
Here's a version using a JMS Topic...
<bean id="connectionFactory" class="org.springframework.jms.connection.CachingConnectionFactory">
<property name="targetConnectionFactory">
<bean class="org.apache.activemq.ActiveMQConnectionFactory">
<property name="brokerURL" value="vm://localhost"/>
</bean>
</property>
<property name="sessionCacheSize" value="10"/>
</bean>
<bean id="requestTopic" class="org.apache.activemq.command.ActiveMQTopic">
<constructor-arg value="topic.demo"/>
</bean>
<bean id="replyQueue" class="org.apache.activemq.command.ActiveMQQueue">
<constructor-arg value="queue.reply"/>
</bean>
<int-stream:stdin-channel-adapter id="stdin" channel="stdinToJmsoutChannel"/>
<int:channel id="stdinToJmsoutChannel"/>
<int:chain input-channel="stdinToJmsoutChannel">
<int:header-enricher>
<int:header name="jms_replyTo" ref="replyQueue" />
</int:header-enricher>
<int-jms:outbound-channel-adapter destination="requestTopic" />
</int:chain>
<int-jms:message-driven-channel-adapter channel="jmsReplyChannel"
destination="replyQueue"/>
<int:channel id="jmsReplyChannel" />
<int:chain input-channel="jmsReplyChannel">
<int:aggregator group-timeout="5000" expire-groups-upon-timeout="false"
send-partial-result-on-expiry="true"
discard-channel="logLateArrivers"
correlation-strategy-expression="headers['jms_correlationId']"
release-strategy-expression="size() == 2"/>
<int-stream:stdout-channel-adapter append-newline="true"/>
</int:chain>
<int:logging-channel-adapter id="logLateArrivers" />
<!-- Subscribers -->
<int-jms:inbound-gateway request-channel="upcase" request-destination="requestTopic" />
<int-jms:inbound-gateway request-channel="upcase" request-destination="requestTopic" />
<int:transformer input-channel="upcase" expression="payload.toUpperCase()" />
Type requests into the console:
Please type something and hit <enter>
foo
[FOO, FOO]
bar
[BAR, BAR]
baz
[BAZ, BAZ]