Why connection.start() need to be called before consumer.rec

[anthonylee]

Hi,

In examples I realized that there is always connection.start() before consumer.receive(),
but it is OK that there is NO connection.start() before producer.send().
It is not so clear for me.
If a connection.start() before producer.send() and consumer.receive() then that is clearer.

Can someone explain a little bit the reason?

Thanks in advance.

[ataylor]

because this is what the JMS spec says it should do :).

connection.start() Starts (or restarts) a connection's delivery of incoming messages.

So you only need it for consumers.

[timfox]

See the JMS javadoc:

http://java.sun.com/javaee/5/docs/api/javax/jms/Connection.html#start%28%29

[anthonylee]

Oh, I see.
Thanks ataylor and tim.

[anthonylee]

So, why the JMS spec make connection.start() for producer.send() implicit but make it explicit for consumer.receive()?

[timfox]

"anthonylee" wrote:
So, why the JMS spec make connection.start() for producer.send() implicit but make it explicit for consumer.receive()?

Connection.start() just means "start *delivering* any messages on this connection", so clearly it's meaningless when applied to *sending* messages.

[anthonylee]

Hi Tim,

Thanks for reply, it helps me understand it clearly.

My confusion came from that I thought *delivery* include sending message too.
Actually, it just means the Queue/Topic begin to allow consumer to receive message.
I tested it, without connection.start(), consumer.receive() didn't receive any message.

Thanks again!

[timfox]

Glad to be of help.

In messaging delivery usually means the transfer of messages from the messaging system to any recipients, whereas sending/publishing/posting is the transfer of messages from the client to the messaging system.

This is similar terminology to how a postal system operates.

When you post a letter, you post it into the post box, you wouldn't say you deliver it to the post box.

The mail company then delivers the message to the recipient.

[anthonylee]

Yes, that is exactly what I was thinking: Postal system.

When you just move to another place, you may inform the post office to hold your mails for 1 month, and then you settle down in new place and tell the post office to begin to deliver mails to new place.

[anthonylee]

The last question is:

For Message Driven Bean, is there a way to start connection like a standalone consumer?

[ataylor]

The connection will be started when the MDB is deployed. This is controlled by the J2EE layer not hornetq.