TUTORIAL J2EE

Distributed Multitiered Applications
The J2EE platform uses a distributed multitiered application model for enterprise

applications. Application logic is divided into components according to function, and

the various application components that make up a J2EE application are installed

on different machines depending on the tier in the multitiered J2EE environment

to which the application component belongs. Figure 1-1 shows two multitiered J2EE

applications divided into the tiers described in the following list. The J2EE

application parts shown in Figure 1-1 are presented in J2EE Components.
Client-tier components run on the client machine. Web-tier components run

on the J2EE server. Business-tier components run on the J2EE server.
Enterprise information system (EIS)-tier software runs on the EIS server.
Although a J2EE application can consist of the three or four tiers shown

in Figure 1-1, J2EE multitiered applications are generally considered

to be three-tiered applications because they are distributed over

three locations: client machines, the J2EE server machine, and the database

or legacy machines at the back end. Three-tiered applications that run in

this way extend the standard two-tiered client and server model by placing

a multithreaded application server between the client application and back-end

storage.

http://java.sun.com/j2ee/1.4/docs/tutorial/doc/