Channel Channel Channel!!

DirectChannel

First of all, DirectChannel is not Pollable Channel. Since it is not Pollable Channel, it is not based on BlockingQueue. I was wrong about that before.

DirectChannel is a Subscribable Channel but with Point-to-point Semantics. It would be easy to understand from the implementation's point of view.

private boolean doDispatch(Message<?> message) {

boolean success = false;

Iterator<MessageHandler> handlerIterator = this.getHandlerIterator(message);

if (!handlerIterator.hasNext()) {

throw new MessageDispatchingException(message, "Dispatcher has no subscribers");

}

List<RuntimeException> exceptions = new ArrayList<RuntimeException>();

while (success == false && handlerIterator.hasNext()) {

MessageHandler handler = handlerIterator.next();

try {

handler.handleMessage(message);

success = true; // we have a winner.

}

catch (Exception e) {

RuntimeException runtimeException = (e instanceof RuntimeException)

? (RuntimeException) e

: new MessageDeliveryException(message,

"Dispatcher failed to deliver Message.", e);

if (e instanceof MessagingException &&

((MessagingException) e).getFailedMessage() == null) {

((MessagingException) e).setFailedMessage(message);

}

exceptions.add(runtimeException);

this.handleExceptions(exceptions, message, !handlerIterator.hasNext());

}

}

return success;

}

DirectChannel picks up the next available Handler and calls its handleMessage() method to send out the message. And that's it.

• It's point-to-point.
• It only call one handler successfully.
• And it won't queue!
• When the message arrives and the handler is not there, it will throw an exception.