Application Client for WAS

 

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In a traditional client-server environment, the client requests a service and the server fulfills the request. Multiple clients use a single server. Clients can also access several different servers. This model persists for Java clients except that now these requests use a client runtime environment.

WAS supports the pluggable client. In this model, the client application requires a servlet to communicate with the enterprise bean, and the servlet must reside on the same machine as the WAS.

The Application Client for WAS V6.1 (Application Client) consists of the following client applications:

• J2EE application client application (Uses services provided by the J2EE Client Container)
• Thin application client application (Does not use services provided by the J2EE Client Container)
• Applet application client application

• ActiveX to EJB Bridge application client application (Windows only)

The Application Client is packaged with the following components:

• Java Runtime Environment (JRE) (or an optional full Software Development Kit) that IBM provides.

• WAS run time for J2EE application client applications or Thin application client applications

• An ActiveX to EJB Bridge run time for ActiveX to EJB Bridge application client applications (Windows only)

• IBM plug-in for Java platforms for Applet client applications (Windows only)

  The Pluggable application client is a kind of Thin application client. However, the Pluggable application client uses a Sun JRE and Software Development Kit instead of the JRE and Software Development Kit that IBM provides.

The ActiveX application client model, uses JNI to programmatically access the JVM API. The JVM code exists in the same process space as the ActiveX application...

• Visual Basic
• VBScript Active Server Pages (ASP)

...and remains attached to the process until that process terminates.

The Applet client model has a Java applet embedded in a HTML document residing on a remote client machine from the WAS. With this type of client, the user accesses an enterprise bean in the WebSphere Application Server through the Java applet in the HTML document.

The J2EE application client is a Java application program that accesses enterprise beans, JDBC APIs, and JMS message queues. The J2EE application client program runs on client machines. This program follows the same Java programming model as other Java programs; however, the J2EE application client depends on the Application Client run time to configure its execution environment, and uses the JNDI name space to access resources.

The Pluggable and Thin application clients provide a lightweight Java client programming model. These clients are useful in situations where a Java client application exists but the application needs enhancements to use enterprise beans, or where the client application requires a thinner, more lightweight environment than the one offered by the J2EE application client. The difference between the Thin application client and the Pluggable application client is that the Thin application client includes a JVM API, and the Pluggable application client requires the user to provide this code. The Pluggable application client uses the Sun JDI, and the Thin application client uses the IBM Developer Kit for the Java platform.

The J2EE application client programming model provides the benefits of the J2EE platform for the Java client application. Use the J2EE application client to develop, assemble, deploy and launch a client application. The tooling provided with the WebSphere platform supports the seamless integration of these stages to help the developer create a client application from start to finish.

When you develop a client application using and adhering to the J2EE platform, you can put the client application code from one J2EE platform implementation to another. The client application package can require redeployment using each J2EE platform deployment tool, but the code that comprises the client application remains the same.

The Application Client run time supplies a container that provides access to system services for the client application code. The client application code must contain a main method. The Application Client run time invokes this main method after the environment initializes and runs until the Java virtual machine code terminates.

The J2EE platform supports the Application Client use of nicknames or short names, defined within the client application deployment descriptor, which identify enterprise beans or local resources...

• JDBC
• JMS
• JavaMail
• URL APIs

...for resolution through JNDI.

This simplified resolution to the enterprise bean reference and local resource reference eliminates changes to the client application code when the underlying object or resource either changes or moves to a different server.

When these changes occur, the Application Client can require redeployment.

The Application Client provides initialization of the run-time environment for client applications, with a deployment descriptor defining unique initializations.

The Application Client run time also provides support for security authentication to enterprise beans and local resources.

The Application Client uses RMI-IIOP, which enables the client application to access...

• enterprise bean references
• CORBA object references

When you combine the J2EE and CORBA environments or programming models in one client application, understand the differences between the two programming models to use and manage each appropriately.

View the Samples gallery for more information about the Application Client.

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Sub-topics

Application client functions
ActiveX application clients
Applet clients
J2EE application clients
Pluggable application clients
Thin application clients