Does this mean that you have seen those 100 messages? Or merely that you think that's what might happen? If you see just one of these, just forget about them. If you see 100 after you have sent 100 messages, then you need to investigate further (in this case I'd suspect that the API that is sending these messages -whatever that means- is not being used correctly).
SEVERE: The web application [/app] appears to have started a thread named [Connection Keep-Alive nullBroker #1@xxx:6849] but has failed to stop it. This is very likely to create a memory leak.