Business Object, General Class - Advanced Java Fat-Client-Development

This document
* describes the mission of the General Class of a Business Object and
* gives a To-Do-List for the steps necessary to code the class.

Prerequisites:

• Business Object, Overview describes the inheritance structure (subclassing) of Business Objects.
  It gives an overview how the subclasses for a business-entity cooperate.

Mission of the General Class:

The General Class of the Business Object, designed for a business entity, comprehends
* variables,
* constants for Stati that might occur when a method is performed and
* methods that are needed both on the subclass for the Client-Side and on the subclass for the Server-Side.

To-Do-List to implement the class:

Please obey, that all General Classes for Business Objects are put into a package (suggestion: application.bo) that is different for those for Client-Side Classes (suggestion: application.boc) and Server-Side Classes (suggestion: application.bos).
This is done to simplify the packaging-script when the application is versioned to run as Client/Server.
The General Classes are needed on both the Client-Application as on the EJB (Enterprise Java Bean) that is running under a JAS (Java Application Server).
The Client-Side Classes are only needed on the Client Application (and packed into the JAR-file for it) while the Server-Side Classes are only needed within the EJB.

A fast way to get the code is to copy from an existing class and modify it.
A class with working code (from the tutorial Develop a Fat-Client in Java) is JS_ErrDB_Project_BO.

Steps to code the class:

• Create a plain java-class under the package 'application.bo'.

• Inherit from the class JSBS_BO :
  Example:
  public class JS_ErrDB_Project_BO extends JSBS_BO {

• Code the variables specific for the business entity the Business Object reflects.
  Example:
  /*
   * Project-Code, that is the shortcut for the Project. */
      public String ProjectCode = "";

• Code the method to copy the variables from another object of this class.
  This method is needed to transfer the data from the Server-Side Object to the Client-Side object.
  This is necessary as the Server-Side Object exists only as long as the database-operation lasts and the data is transferred to the client.
  (It is handled as a 'transaction' like it was with CICS, IMS/DC, etc. - if some old folks can remember ;-) )
  Example:
  /*
 * --------------------
 * Method to copy the values from another object into this object. */
    public void getJS_ErrDB_Project_BO(JS_ErrDB_Project_BO parmJS_ErrDB_Project_BO) {
/*
 * Use the method of the super-class to copy the Common Attributes,
 * StatusCode and StatusMsg. */
        super.getJSBS_BO(parmJS_ErrDB_Project_BO);
        ProjectCode = parmJS_ErrDB_Project_BO.ProjectCode;
        LanguageCode = parmJS_ErrDB_Project_BO.LanguageCode;
        TargetDirectory = parmJS_ErrDB_Project_BO.TargetDirectory;
    }

If a variable is another Business Object, use the copy-method of this object to copy.
Example:
        InvoicePositions.getJS_HSepp_InvoicePositionList_BO(parmJS_HSepp_Invoice_BO.InvoicePositions);

• Code the method to check if a Business variable (variables that are not Common Attributes) is different from that of another object.
This method is needed to check if a change to the Business Object was made.
This will save some database-access-time if the user did not change something and requests a 'store'.
Example:
/*
 * --------------------
 * Method to compare two Business Objects and check if
 * at least one of the Business Attributes is different. */
    public boolean isDifferent(JS_ErrDB_Project_BO parmJS_ErrDB_Project_BO) {
/*
 * Use the method of the super-class to copy the Common Attributes,
 * StatusCode and StatusMsg. */
        if (this.ProjectCode != parmJS_ErrDB_Project_BO.ProjectCode) return true;
        if (this.LanguageCode != parmJS_ErrDB_Project_BO.LanguageCode) return true;
        if (this.TargetDirectory != parmJS_ErrDB_Project_BO.TargetDirectory) return true;
        return false;
    }

If a variable is another Business Object, use the copy-method of this object to copy.
Example:
        InvoicePositions.getJS_HSepp_InvoicePositionList_BO(parmJS_HSepp_Invoice_BO.InvoicePositions);

The next implementation steps (for this class) may arise as the specifications are more detailed analyzed.
If you are going to have a feedback how the basic implementation works (e.g. to see and correct semantical misconceptions), it is recommended to start coding the Client-Side Class of the Business Object.
To to this, please follow this link.

• Code the constants specific for the Business Object.
The requierement mostly arises when the Server-Side subclass for the Business Object are developed and coded.
Code the constants as the demand for them arises.

• Code the methods specific for the Business Object.
There is no general guideline which additional methods are needed..

top.

Related Documents:

• A simplified overview how data is written to / read from a database:
Using Business Objects to handle data-storage and retrieval.