Spring Integration - Convert Service Activator with Java Configuration - spring

Question

I try to convert the "Hello World example" from Spring Integration samples (https://github.com/spring-projects/spring-integration-samples/tree/master/basic/helloworld) from XML, to Java Configuration, (so with the #Configuration annotation).
The configuration class looks like this :
#Configuration
#EnableIntegration
public class BasicIntegrationConfig{
#Bean
public DirectChannel inputCHannel() {
return new DirectChannel();
}
#Bean
public QueueChannel outputChannel() {
return new QueueChannel();
}
#Bean
#ServiceActivator(inputChannel= "inputChannel", outputChannel= "outputChannel" )
public MessageHandler fileWritingMessageHandler() {
MessageHandler mh = new MessageHandler() {
#Override
public void handleMessage(Message<?> message) throws MessagingException {
System.out.println("Message payload: " + message.getPayload());
}
};
return mh;
}
}
To test it, I use the main() supplied from sample project :
DirectChannel fileChannel = applicationContext.getBean("inputChannel", DirectChannel.class);
QueueChannel outputChannel = applicationContext.getBean("outputChannel", QueueChannel.class);
System.out.println("********** SENDING MESSAGE");
fileChannel.send(new GenericMessage<>("test"));
System.out.println(outputChannel.receive(0).getPayload());
I see in the console "Message payload: test", but unfortunately, I don't receive the message on the outputchannel (I have a NullPointerException on outputChannel.receive(0).
Do you have an idea why the Service Activator does not send the message to the output channel?

Answer 1

Your MessageHandler returns void.
You need to subclass AbstractReplyProducingMessageHandler instead.

Answer 2

Thank you Gary, it works perfectly after switching to :
#Bean
#ServiceActivator(inputChannel= "inputChannel")
public AbstractReplyProducingMessageHandler fileWritingMessageHandler() {
AbstractReplyProducingMessageHandler mh = new AbstractReplyProducingMessageHandler() {
#Override
protected Object handleRequestMessage(Message<?> message) {
String payload= (String)message.getPayload();
return "Message Payload : ".concat(payload);
}
};
mh.setOutputChannelName("outputChannel");
return mh;
}
As a side note, I had to remove the output channel attribute in #ServiceActivator annotation, and put it in method body instead (Bean Validation Exception if not).