This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
The onMessage() method of MessageListener interface is called whenever a message arrives at the queue, to which it is registered. Therefore, I don't see the meaning of "how to get all messages in the queue". It will be called whenever a message arrives to the queue automatically.