if the sender sends the message using pub/sub, suppose if the receiver is not available, then what will happen??
The message will be sent to the topic and will stay there until either the subscribers receive it or the message time to live expires, the server shuts down (for nondurable subscriptions) or the topic is deleted.
suppose sender want to rollback the message, how can he do??
You can use transactions with jms as well. JMS supports two types of transactions: transacted sessions and JTA transactions. Regards.