Chapter 3 EAServer and Application Issues

Client application development

If you are familiar with EAServer, writing client applications that use Application Integrator components is a straightforward task. Because an Application Integrator component is defined in EAServer as are other Java components, writing client applications is similar to writing applications for non-Application Integrator components.

For example, building client applications in EAServer consists of the following steps:

1. Generate the stub classes.
2. Write the application logic, including:
   1. Instantiate proxy instances.
   2. Execute component methods.
   3. Process results.
   4. Handle errors.
3. Deploy the application.
   
   See the EAServer Programmer's Guide for details on perform these tasks.

   All IDL modules for Application Integrator components are defined with the module property com.sybase.jaguar.module.java.package set to the Java package name that was specified for this component in the Component Builder. Therefore, this is also the Java package name for Java stubs generated for Application Integrator components.

When you write client applications in EAServer, you should understand the following characteristics of Application Integrator components:

• Components can contain one or more methods.
• Each method corresponds to a target stored procedure.
• The input and output parameters for each method are mapped to parameters in the procedure. Typically, only procedures can have output parameters.
• The return type of the method is based on whether result sets are returned from the procedure. The number of result sets maps to IDL statements as follows:

  Number of result sets	IDL mapping
  0	void
  1	TabularResults::ResultSet
  More than 1	TabularResults::ResultSets

• If the target stored procedure has a return value, it appears in the method signature as an output parameter.
• Parameters declared as nullable cause Application Integrator to add a parameter (with the same mode as the nullable parameter) to the method to communicate whether the corresponding parameter contains a NULL value.
• Exceptions caught by the component are propagated to the client stub as a user-defined exception type of AIUserException. These exceptions contain a single field called Message that contains the error message text for the exception.

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