Papi-provider-queue is a project mainly written in Java, it's free.
A queue framework for single-threading implementation of SOPERA PAPI-based providers
This is a simple example on how to create the SOPERA Provider that is handling requests within a single Thread.
In SOPERA PAPI we have a limitation that once MessageHandler recieved a message it should read and respond to it in the same thread. This limitation could be avoided by using the QueuedMessageHandler class.
See example inside org.sopera.talend.test.TestProviderQueue.
Basically I can add a usefull feature! :-)