How to Integrates a new functionality code to Java-EE application?

I have built a simple java-ee system and I want users to extends its functionality by developing an independent java application and upload it to my server as a .jar file.

My system is using EJB-3.2 to implement the business logic which is a list of services where each service is represented by a stateless session bean.

Is it a good practice to integrate a .jar files to the system like here, here, or here? What are the best practices used to integrate new code to a java system?

Thanks in advance.