I know that mdb is stateless. But, If I use instance variables just for one invocation of the mdb, for saving me passing parameters to methods, is it ok, or the bean can be used again even if the onMessage method did not finish?
One instance is used to serve one onMessage()... it is safe to use instance variables for a single invocation... but not safe to use these variables for multiple invocations as different invocations might be served by different instances...