Question

I have client and server threads in my applications. When I run these apps as standalone apps, these threads communicate properly.

But when I run client as JUnit and server as standalone, client thread dies within few seconds.

I couldn’t get, why such different behavior.

Answer 1

When the JUnit runner terminates, all spawned threads etc. are killed too (as it is most likely run in a separate JVM instance).

Here is a (rather old) article describing the problem you experienced (the GroboUtils library it is recommending seems to have been abandoned long time ago though). And another, recent one, with a more modern solution using the new Java concurrency framework.

The gist of the latter solution is that it runs the threads via an executor, which publishes the results of the runs via Futures. And Future.get is blocking until the thread finishes with the task, automatically keeping the JUnit tests alive. You may be able to adapt this trick to your case.