EAR (Enterprise Application aRchive) is a file format used by Jakarta EE for packaging one or more modules into a single archive so that the deployment of the various modules onto an application server happens simultaneously and coherently.
The JBoss application servers before Version 5 were notable in that it does not isolate deployed components.
The Unified Classloader design reduces communications overhead between running applications, as class data can be shared by reference or simple copies.
It also allows developers to avoid having to understand the problems that a tree of classloaders can create.
However, it prevents different versions of dependent libraries from being deployed in separate applications.