To use FKache you need to take the FKache jar file and put in the server library folder and restart the server, so it can be accessed from all usercode, such as Servlets, EJBs etc. Do not put it as a library inside a WAR/EAR/EJB-JAR, as its not designed for this use in mind. You also need to install the concurrent.jar into the same location. If your server already uses Dough Lea's concurrency library, its not neccessary to install this. JBoss 2.4 and upwards has concurrency.jar pre-installed.