what are the contents of J2EE and where it is used in compters?

Answer 1

J2EE stands for "Java 2 Enterprise Edition," though the latest edition is version 5 so it is now called just "Java EE." It is a framework for implementing scalable/modular software solutions. Sun's web site (see "sources") says:

"Java Platform, Enterprise Edition (Java EE) is the industry standard for developing portable, robust, scalable and secure server-side Java applications. Building on the solid foundation of the Java Platform, Standard Edition (Java SE), Java EE provides web services, component model, management, and communications APIs that make it the industry standard for implementing enterprise-class service-oriented architecture (SOA) and next-generation web applications."

We use J2EE for the "middle tier" of our corporate systems. The upper tier is the web servers, the middle tier is all the business logic, and the back end is a number of databases.

Answer 2

J2EE is a middleware component, which consists of Application Server , Web Server.
It's used to develop and deploy a Web based application on the Internet.

Answer 3

I'm not that familiar with J2EE, but I thought the main feature it had was the container that executed Java Beans, and allowed for deploying the beans across multiple machines, and a directory service to manage resources. That way you can divide the application vertically, by "layer", as well as horizontally between peers in each layer.

This architecture competes with Microsoft's COM technology (aka COM+ aka .NET aka DCOM), and competes with CORBA. It's been successful, and has inspired .NET.