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 Head First EJB book MDB chapter says that queues are not ordered. The ordering of messages is not guaranteed and we should not program depending on an order. The JMS book by RMH says that queue messages will be ordered and will be delivered to the receivers in the same order in which they were delivered to the queue by the message server. So which is right? Are queue messages ordered or unordered? Are they guaranteed to be delivered to the receiver in the same order in which they were sent by the sender? What happens if there are multiple receivers? Will that affect the ordering? Please clarify.
As far as I know you cannot code according to the order of messages because if one message fails (transaction rolled back) then it is placed at the back of the queue behind any messages that were posted before it.