The three-tier Web application architecture generally includes the connection of a server-side Java application to the database through a JDBC connection (see Figure 2-3). In this pattern, TopLink resides within a Java server (a J2EE server or a custom server), with several possible server integration points. The application can support Web clients such as servlets, Java clients, and generic clients using XML or Common Object Request Broker Architecture (CORBA).

The three-tier application is a common architecture in which TopLink resides within a Java server (either a J2EE server or a custom server). In this architecture, the server session provides clients with shared access to JDBC connections and a shared object cache. Because it resides on a single JVM, this architecture is simple and easily scalable. The TopLink persistent entities in this architecture are generally Java objects.

This architecture often supports Web-based applications in which the client application is a Web client, a Java client, or a server component.

Although not all three-tier applications are Web-based, this architecture is ideally suited to distributed Web applications. In addition, although it is also common to use EJB in a Web application, this TopLink architecture does not.

Example Implementations

Examples of three-tier architecture implementation include the following:

* A Model-View-Controller Model 2 architectural design pattern that runs in a J2EE container with servlets and JSP that uses TopLink to access data without EJB.
* A Swing or Abstract Window Toolkit (AWT) client that connects to a server-side Java application through RMI, without an application server or container.

Advantages and Disadvantages

The three-tier Web application architecture offers the following advantages:

* High performance, lightweight persistent objects
* High degree of flexibility in deployment platform and configuration

The disadvantage of this architecture is it is less standard than EJB.

Attached Images

3tierov.gif (19.4 KB, 1 views)

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