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   Using BEA Jolt

The Jolt Class Library gives the BEA Tuxedo application developer the tools to develop client-side applications or applets that run as independent Java applications or in a Java-enabled Web browser. The bea.jolt package contains the Jolt Class Library. To use the Jolt Class Library, the client program or applet must import this package. For an example of how to import the bea.jolt package, refer to the listing Jolt Transfer of Funds Example (SimXfer.java).

Java programs that run in a browser are called applets. Applets are small, easily downloaded parts of an overall application that perform specific functions. Many popular browsers impose limitations on the capabilities of Java applets in order to provide a high degree of security for the users of the browser. Applets have the following restrictions:

• An applet ordinarily cannot read or write files on any host system.

• An applet cannot start any program on the host (client) that is executing the applet.

• An applet can make a network connection only to the host from which the applet originated; it cannot make other network connections, not even to the client machine.

Programming workarounds exist for most restrictions on Java applets. Check your browser's Web site (for example, www.netscape.com or www.microsoft.com) or developer documentation for specific information about the applet capabilities that the browser supports or restricts. You can also use Jolt Relay to work around some of the network connection restrictions.

The Jolt Class Library has the following characteristics:

• Features fully thread-safe classes.

• Encapsulates typical transaction functions such as logon, synchronous calling, transaction begin, commit, rollback, and logoffs as Java objects.

• Contains methods that allow you to set idle time-outs for continuous and intermittent client network connections.

• Features methods that allow a Jolt client to subscribe to and receive event-based notifications.

Error and Exception Handling

The Jolt Class Library returns both Jolt interpreter and BEA Tuxedo errors as exceptions. The Jolt Class Library Reference contains the Jolt classes and lists the errors or exceptions thrown for each class. The API Reference in Javadoc contains the Error and Exception Class Reference.

BEA Jolt works in a distributed client/server environment and connects Java clients to BEA Tuxedo based applications.

The following figure illustrates the client/server relationship between a Jolt program and the Jolt Server.

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As illustrated in the figure, the Jolt Server acts as a proxy for a native BEA Tuxedo client, implementing functionality available through the native BEA Tuxedo client. The BEA Jolt Server accepts requests from BEA Jolt clients and maps those requests into BEA Tuxedo service requests through the BEA Tuxedo ATMI interface. Requests and associated parameters are packaged into a message buffer and delivered over the network to the BEA Jolt Server. The BEA Jolt Connection Manager handles all communication between the BEA Jolt Server and the BEA Jolt applet using the BEA Jolt Transaction Protocol. The BEA Jolt Server unpacks the data from the message, performs any necessary data conversions, such as numeric format conversions or character set conversions, and makes the appropriate service request to BEA Tuxedo as specified by the message.

Once a service request enters the BEA Tuxedo system, it is executed in exactly the same manner as any other BEA Tuxedo request. The results are returned through the ATMI interface to the BEA Jolt Server, which packages the results and any error information into a message that is sent to the BEA Jolt client applet. The BEA Jolt client then maps the contents of the message into the various BEA Jolt client interface objects, completing the request.

On the client side, the user program contains the client application code. The Jolt Class Library packages a JoltSession and JoltTransaction, which in turn handle service requests.

The following table describes the client-side requests and Jolt Server-side actions in a simple example program.

Jolt Client/Server Interaction

Jolt Client		Jolt Server
1	attr=new JoltSessionAttributes(); attr.setString(attr.APPADDRESS, "//myhost:8000");	Binds the client to the BEA Tuxedo environment
2	session=new JoltSession(attr, username, userRole, userPassword, appPassword);	Logs the client onto BEA Tuxedo
3	withdrawal=new JoltRemoteService( servname, session );	Looks up the service attributes in the Repository
4	withdrawal.addString("accountnumber", "123"); withdrawal.addFloat("amount", (float) 100.00);	Populates variables in the client (no Jolt Server activity)
5	trans=new JoltTransaction( time-out, session);	Begins a new Tuxedo transaction
6	withdrawal.call(trans);	Executes the BEA Tuxedo service
7	trans.commit() or trans.rollback();	Completes or rolls back transaction
8	balance=withdrawal.getFloatDef("balance," (float) 0.0);	Retrieves the results (no Jolt Server activity)
9	session.endSession();	Logs the client off of BEA Tuxedo

The following tasks summarize the interaction shown in the previous table, Jolt Client/Server Interaction.

1. Bind the client to the BEA Tuxedo environment using the JoltSessionAttributes class.

2. Establish a session.

3. Set variables.

4. Perform the necessary transaction processing.

5. Log the client off of the BEA Tuxedo system.

Each of these activities is handled through the use of the Jolt Class Library classes. These classes include methods for setting and clearing data and for handling remote service actions. Jolt Object Relationships describes the Jolt Class Library classes in more detail.