In JMS, the only portable solution to determine the number of messages in a queue is to create a javax.jms.QueueBrowser object. With the QueueBrowser, you can enumerate and count the messages in the queue, without consuming the messages.
This works well if the queue is rather small (up to 100 messages maybe), but can be very time consuming if there are many messages in the queue.
A JMS provider can offer administration APIs that allow you to obtain the number of message in a queue, in a more efficient manner. But these are vendor proprietary extensions and limit the portability of your JMS application.
This was first published in February 2002