Project Notes

Project: CORBA Reference Application

•  Cliffhanger Adventure Gear Credit Approval Server
•  Cliffhanger Adventure Gear Credit Approval Applet

Description:
This sample provides an example of a credit approval/credit card issuing system for a fictitious company selling outdoor adventure gear. The company, Cliffhanger Adventure Gear, requires an automated system for processing the credit history of an applicant to determine if a credit card should be issued.  If a credit card is issued, the system calculates the credit limit and expiration date for the account.

The sample consists of two JBuilder projects, a Credit Approval Server application and a Credit Approval Client applet. The Credit Approval Server and Credit Approval Applet communicate by means of a set of CORBA objects, illustrating how to create and use CORBA objects in JBuilder. Generation of Java code from IDL source, a server application, a client applet, and a callback are demonstrated. For simplicity, the client and server are set up to run on the same machine. This sample also provides an example of using JBuilder's DataExpress database components to enforce a set of business rules.

Setup
To run this sample, you must

• Use a version of JBuilder that includes the JBuilder DataExpress database architecture components.

  Note: All versions of JBuilder provide direct access to SQL data through the JavaSoft JDBC API. Some versions of JBuilder provide additional DataExpress components (on the Data Access tab of the Component Palette) that greatly simplify RAD visual development of database applications. Refer to the JBuilder product page from the Borland Web site for availability of features in each JBuilder version.

• Have the Visigenic VisiBroker for Java ORB installed. It's installed, along with this application, when you perform a "Typical" JBuilder installation or select "Visigenic's VisiBroker Files" in a "Custom" installation.

• Have Local InterBase and the Visigenic ODBC driver for InterBase installed. Local InterBase can be installed from the main JBuilder Client/Server installer. Within the InterBase installation, there is an option to install the ODBC driver.

• Have the main Cliffhanger reference application installed, have its database, CLIFFHANGER.GDB, available, and have an ODBC data source called "Cliffhanger" that points to it. The application is installed if you select the "Typical" JBuilder installation or the "Reference Applications" option of the "Custom" installation.

• Define another ODBC data source. The Cliffhanger Credit Approval application includes in its Db subdirectory an InterBase database called ACMECreditBureau.GDB. To define an ODBC data source called "AcmeCreditBureau" that points to it:
  • Launch "32bit ODBC" from the Windows Control Panel
  • Click the Add button
  • Select the Visigenic InterBase driver and click Ok
  • Set Data Source Name to "AcmeCreditBureau"; set Database to the fully-qualified name of the database (usually C:\JBuilder\samples\borland\reference\creditapproval\db\ACMECreditBureau.GDB."); set Username to "SYSDBA"; and set Password to "masterkey"
  • Click Test Connect. Correct the information entered if necessary; when it's okay, click Ok and close the Data Sources dialog.

Executing the Sample
To execute the CORBA sample, follow this order of events:

1. Start the VisiBroker OSAGENT.EXE executable, which is located in JBuilder\bin. On Windows NT, use the -C command line parameter. "VisiBroker Smart Agent" appears on the Windows Taskbar.
2. Execute the Server portion of this sample: CreditApprovalServer.jpr. The server runs and displays messages in a console window. You should see the message "Awaiting client requests".
3. Execute the Client applet portion of this sample: CreditApprovalClient.jpr. Enter the data required to apply for a credit card and click the Submit button. The request is sent to the server, which processes it and sends a response back to the client applet.
   

Other documentation and data files
One other document included in this sample, Reusable Code, highlights some of the reusable code snippets from this sample project that might be useful for your own JBuilder projects.

In addition to the InterBase database ACMECreditBureau.GDB, this application's Db directory contains text files that can be used to generate clean copies of the CLIFFHANGER.GDB and ACMECreditBureau.GDB databases. To use them:

• First, be sure you want to discard an existing database. If you don't, move it to a safe place before continuing.
• Run the "InterBase Windows ISQL" tool from the InterBase program group.
• Choose File | Run an ISQL Script.
• To delete ACMECreditBureau.GDB and re-create it, navigate to "ACME schema.sql" and select it.
• Choose to save output to a file, and supply a name.
• If there are errors, check the output file, correct them, and repeat these steps.
• This will create a new ACMECreditBureau.GDB in the directory that "ACMESchema.sql" is in and fill it with sample data.
• To delete and re-create CLIFFHANGER.GDB, follow the same steps, but run the db.sql script first, then DataStock.sql.

Description:
The Approval Server is responsible for reviewing an applicants credit history and to make a determination as to whether the applicant should or should not be approved for a Cliffhanger Credit Card.  The server also issues credit cards to approved applicants consisting of a credit card number, an expiration date and a credit limit.

The server uses two databases:

1. The Cliffhanger Database: This database contains Cliffhanger Credit Card account information such as card holder information, credit card number, expiration date, balance, credit limit and account status.  Records are created in this database when an applicant is issued a credit card.
2. The ACME Credit Bureau Database: This database contains account history for all active/inactive accounts of people tracked by the ACME Credit Bureau.  This database is used in the Credit Card Approval process. Since using real credit history information is not feasible, this database is populated using randomly generated, fictional sample data.

•  Using IDL to Generate Java Classes
•  ORB Usage
•  Data Module

Using IDL to Generate Java Classes
The first step in creating CORBA objects is defining their interfaces using IDL. The IDL defined interfaces for this project are located in CreditApproval.idl.  Interfaces only need to be created for objects that are going to be distributed using CORBA.
Once these interfaces have been defined, use JBuilder's CORBA Settings Wizard (from Tools | CORBA Settings) to create Java helper interfaces and classes.  For this project, these generated classes are located in the CreditApprovalCORBAInterface package.  Files generated with the _example_  prefix demonstrate how to use the Java classes and interfaces generated by the wizard.

The CreditApprobal.idl interface file demonstrates the following:

• Definition of Structures - IDL defined structures appear in Java as classes.
• Definition of Exceptions - CORBA Exceptions can be thrown and caught across process boundaries.
• Definition of Class Interfaces

ORB Usage
CORBA Class implementation, initialization, registration and usage are demonstrated by the following classes:

CreditApprovalServer Class demonstrates the following:

• Initialization of the ORB
• Creation and registration of a CORBA object
• Processing of CORBA Service Requests

• Creation and registration of a pool of CORBA objects. This technique is outlined in Client/Server Programming with Java and CORBA by Robert Orfali and Dan Harkey; John Wiley & Sons, 1997.

• Use of a transient callback class to provide status information to the client
• Use of the IDL defined CORBA exceptions

Data Module
Three data module classes are used in this sample.  These classes contain Database components, QueryDataSet components, and all the business rules logic. Data modules simplify reuse and multiple use of collections of dataset components.

One of these data modules, the CreditHsitoryReviewer class, demonstrates the following:

• Connecting to the sample InterBase database, ACMECreditBureau.GDB, using the Database and QueryDataSet components via JDBC. (See the "Connecting to a database using JDBC" and "Querying a database" topics in the Database Application Developer's Guide)
• Using QueryDataSet components to obtain record sets used in aggregate processing.

Description:
The Credit Approval Applet is used to collect information from the user to be processed by the Credit Approval Server.

The Credit Approval Applet notes are divided into discussions of demonstrated features as follows:

•  ORB Usage
•  Required Field Processing

ORB Usage
This Applet uses CORBA to communicate with the server.  To receive status information, the applet creates a callback CORBA object that is passed to the server.  The following classes demonstrate ORB usage:

The CallbackThread class demonstrates the following:

• Creation of a transient CORBA object
• Use of a thread to process CORBA Service Requests.

• Broadcast of server status information through the use of observer/observables.

• Binding to a persistently named CORBA object: the Credit Approval Dispenser. This object is created, registered and serviced by the Credit Approval Server.
• Processing of thrown CORBA exceptions.

Required Field Processing
Required field processing is an important part of data entry.  A form cannot be submitted for processing until all required fields are complete. The applet uses a couple of techniques to notify the user of missing required fields.

1. The applet displays the name of the next required column that does not contain a value in the status line.
2. When the user attempts to submit an incomplete form, the applet displays a message to the user indicating the missing required field and then sets focus to that field.

• Use of a TableDataSet for the sole purpose of data entry.  This allows for the use of edit masks and required field processing associated with DataSets and Columns.
• Use of a status line to display the next required field that does not contain a value. This allows the user to more efficiently complete the form.

• Determination of the next required field in a DataSet that does not contain a value.
• Determination of the control within a Container that is associated with a specified DataSet column.  This allows the applet to set focus to the control of the next required column that does not contain a value.  This is used when the user attempts to submit an incomplete form for processing.