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Background documentation J2EE Application Concepts  Locate the document in its SAP Library structure

JavaÔ 2 Enterprise Edition Specification, version 1.3, defines an extensible and reliable platform for building high-volume, secure and scalable business Web applications. It defines two types of Web components that can build a J2EE Web application and a runtime environment where they run.

The Web components are:

·        JavaÔ Servlets – defined by Java Servlet Specification, version 2.3.

·        JavaÔ Server Pages (JSP pages) – defined by JavaÔ Server Pages Specification, version 1.2.

They receive client requests through the underlying Web Container, process them and return dynamically generated responses back to the client.

The runtime environment where Web components reside is referred to as the Web Container.

Web Application Models

Most J2EE Web applications use HTTP to communicate with clients. The client is often a Web browser. Depending on where the business logic of the application is implemented, we differentiate two basic application models:

Simple Two-tier Application

The simple two-tier model enables a JSP page (or a servlet) to access external resources such as a database or other legacy applications directly to service client requests. The advantage of such a scheme is that it is simple to design and easy to program. However, this architecture does not scale for a large number of simultaneous clients, because each one must establish or share a potentially scarce and costly connection to the backend resource(s). It also does not provide clear separation of the presentation logic from the business logic, which makes maintenance of such an application a tiresome job.

Two-tier Application Model

This graphic is explained in the accompanying text

N-tier Application

In this model, the application is composed of three or more tiers, where the JSP page or the servlet (located in the middle tier) interact with the backend resources using an EJB component. The EJB and the EJB Container provide managed access to resources, thereby addressing the performance issues. This is the programming model that separates the presentation layer from the business logic and is the central application model of the J2EE platform.

N-tier Application Model

This graphic is explained in the accompanying text

For more information about EJB components and the J2EE Engine EJB Container, see Developing Enterprise JavaBeans.

 

 

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