message-driven-channel-adapter and jms channel?

[jebscar]

Whats the difference betweeen these two configs (or is there one)?

	<int-jms:channel id="exampleChannel" connection-factory="connFactory" queue="inQueue" message-driven="true" />

	<int-jms:message-driven-channel-adapter id="jmsIn" connection-factory="connFactory" destination="inQueue" channel="exampleChannel"/>

[oleg.zhurakousky]

Have you read this:
http://static.springsource.org/sprin...e/#jms-channel
and this
http://static.springsource.org/sprin...hannel-adapter

Don't get me wrong, the reason why I am asking is if it is not clear from the documentation we would like to know what is not clear so we can improve.

[jebscar]

Oleg, I have read and re-read so many times that I think I am confusing myself. If I read correctly, JMS channels, are really on useful when performing async messaging within the same application. Messaging between two SI apps are probably better serve by an outbound-channel-adapter on one side and a message-driven-channel-adapter. Would that be save to say?

[oleg.zhurakousky]

Well, yes you are correct.
However the interesting thing is that you can accomplish async communication even without JMS, by simply configuring a channel as an Executor Channel http://static.springsource.org/sprin...ingle/#channel

So the question is really about wether you need to have JMS in between, One of the use case could be *reliability* where you may have persistent JMS destination which can guarantee that the message will not be lost.

Another use case could be that the JMS destination is a Topic which would mean you can have another external subscriber also retrieving that message etc...

Let me know if that clarifies.

[menulis]

I believe there is one significant difference between a jms:channel and a pair of ordinary int:channel and jms:outbound-channel-adapter.

If the intention is to fire and forget (e.g. using wire-tap) a message to the JMS backed channel, following configuration will not work if there is no listener (e.g. jms:message-driven-channel-adapter) available at the time message is sent to the channel:

<jms:channel
	id="logger"
	queue="logQueue"
	message-driven="false"
/>

It will throw ChannelResolutionException exception:

org.springframework.integration.support.channel.ChannelResolutionException: no output-channel or replyChannel header available

I believe this is not always the desired behavior since JMS messages might be consumed later and/or by different process. In order to avoid this exception, you a pair of ordinary int:channel and jms:outbound-channel-adapter is needed:

<int:channel id="logger"/>
<jms:outbound-channel-adapter
	channel="logger"
	destination="logQueue"
/>

Since message-driven attribute of jms:channel is not documented, I would expect setting it to true should not even set the channel to pollable, but also not to require JMS listener.

The difference between jms:channel and jms:outbound-channel-adapter shall definitely be underlined in the documentation along with an explanation of message-driven attribute of jms:channel.