Spring Integration Load Balance to JMS Queues - spring-integration

Question

I would like to take JMS msgs from a single input queue and fan them out onto N output queues.
I have a simple flow that will forward messages to a single destination but can not figure out how to apply LoadBalancer to allow for multiple destinations in round-robin fashion.
Any ideas how to do this?
#Configuration
public class TestLoadBalance {
public static final String INPUT_QUEUE = "_dev.lb.input";
public static final String OUTPUT_QUEUE_PREFIX = "_dev.lb.output-";
#Bean
public IntegrationFlow testLoadBalanceFlow(
ConnectionFactory jmsConnectionFactory) {
IntegrationFlow flow = IntegrationFlows.from(
Jms.messageDrivenChannelAdapter(jmsConnectionFactory)
.destination(INPUT_QUEUE)
)
.handle(buildOutput(jmsConnectionFactory, 1))
// cant have 2nd handle. gets warn & flow end:
// The 'currentComponent' (org.springframework.integration.jms.JmsSendingMessageHandler#516462cc)
// is a one-way 'MessageHandler' and it isn't appropriate to configure 'outputChannel'
//.handle(buildOutput(jmsConnectionFactory, 2))
.get();
return flow;
}
private JmsSendingMessageHandler buildOutput(ConnectionFactory jmsConnectionFactory, int i){
return Jms.outboundAdapter(jmsConnectionFactory)
.destination(OUTPUT_QUEUE_PREFIX + i).get();
}
}

Answer 1

There are a couple of ways to do it; you can either have multiple subscribers on the channel...
#Bean
public IntegrationFlow inbound(ConnectionFactory cf) {
return IntegrationFlows.from(Jms.messageDrivenChannelAdapter(cf)
.destination("foo"))
.channel(roundRobin())
.get();
}
#Bean
public DirectChannel roundRobin() {
return new DirectChannel();
}
#Bean
public IntegrationFlow outbound1(ConnectionFactory cf) {
return IntegrationFlows.from(roundRobin())
.bridge() // otherwise log() will wire tap the roundRobin channel
.log()
.log(new LiteralExpression("Sending to bar"))
.handle(Jms.outboundAdapter(cf)
.destination("bar"))
.get();
}
#Bean
public IntegrationFlow outbound2(ConnectionFactory cf) {
return IntegrationFlows.from(roundRobin())
.bridge() // otherwise log() will wire tap the roundRobin channel
.log()
.log(new LiteralExpression("Sending to baz"))
.handle(Jms.outboundAdapter(cf)
.destination("baz"))
.get();
}
Or, you can use a destination expression:
#Bean
public AtomicInteger toggle() {
return new AtomicInteger();
}
#Bean
public IntegrationFlow inbound(ConnectionFactory cf) {
return IntegrationFlows.from(Jms.messageDrivenChannelAdapter(cf)
.destination("foo"))
.handle(Jms.outboundAdapter(cf)
.destinationExpression("#toggle.getAndIncrement() % 2 == 0 ? 'bar' : 'baz'"))
.get();
}
#JmsListener(destination = "bar")
public void bar(String in) {
System.out.println("received " + in + " from bar");
}
#JmsListener(destination = "baz")
public void baz(String in) {
System.out.println("received " + in + " from baz");
}
Result:
received test1 from bar
received test2 from baz

Answer 2

Based on Gary's examples I went with the destinationExpression approach as:
#Configuration
public class TestLoadBalance {
public static final String INPUT_QUEUE = "_dev.lb.input";
public static final String OUTPUT_QUEUE_PREFIX = "_dev.lb.output-";
#Bean
public JmsDestinationPartitioner partitioner() {
return new JmsDestinationPartitioner(OUTPUT_QUEUE_PREFIX,1,3);
}
#Bean
public IntegrationFlow testLoadBalanceFlow(
ConnectionFactory jmsConnectionFactory) {
IntegrationFlow flow = IntegrationFlows.from(
Jms.messageDrivenChannelAdapter(jmsConnectionFactory)
.destination(INPUT_QUEUE)
)
.handle(Jms.outboundAdapter((jmsConnectionFactory))
.destinationExpression("#partitioner.nextDestination()"))
.get();
return flow;
}
}
With a wrapper around AtomicInt to handling naming with a prefix:
public class JmsDestinationPartitioner {
private int min;
private int max;
private String prefix;
private AtomicInteger current;
public JmsDestinationPartitioner(String prefix, int min, int max){
this.prefix = prefix;
this.min = min;
this.max = max;
current = new AtomicInteger(min);
}
public int getAndIncrement(){
int i = current.get();
current.getAndIncrement();
if (current.get() > max){
current.set(min);
}
return i;
}
public String nextDestination(){
return prefix + getAndIncrement();
}
}