Implementing an existing interface

You can create PowerBuilder implementations of existing interfaces using the EAServer Component Wizard on the Target or PB Object tab in the New dialog box. A typical use of this feature is to create an implementation of a standard API, such as protocols for online banking and securities trading.

On the Specify Interface Implementation page in the wizard, select Implement an Existing EAServer Remote Interface, then select the EAServer profile for the server that contains the IDL interface you want to implement. You can select only one interface from the list that displays when you expand the list of packages in the wizard.

For PowerBuilder components, the interface name is usually the same as the component name, but the list of interfaces does not map directly to the list of components on the server. The list includes all IDL modules of type interface.

Once you have selected the interface to implement, you can enter the EAServer name for the component. The name of the PowerBuilder custom class user object cannot be changed—it is always the same as the name of the remote interface. You can set most other options, such as package name, instance pooling, and so forth, as if you were creating a new interface.

If you are building a PowerBuilder implementation of a standard API, you will usually use the component name of the remote component, but you should not use the same package name.

Since the interface of the remote component cannot be changed, options that would change method signatures, such as supporting NULL values for arguments, cannot be set in the wizard.

In the custom class user object created by the wizard, public attributes of the remote interface are represented as public instance variables, and public methods as public functions. The scripts for functions contain return statements so that they do not produce compilation errors, but you need to provide a script to implement each function. If the remote interface includes other dependencies, such as structures, the wizard creates them in the same PBL as the user object.

If you are using EAServer 6.0 or later, PowerBuilder components are wrapped as EJB components, and a Remove method is generated by EAServer as part of the component interface. You do not need to use this method.

You can edit the user object just as you would any other custom class user object—the User Object painter does not impose any restrictions. However, you should not make any changes that affect its interface. You should not delete any instance variables and functions that correspond to attributes and methods in the existing interface or change their mode from public to private or protected. Functions cannot be overloaded and the return value or arguments cannot be NULL values.

The project created by the wizard contains information about the interface from which the wizard built the component. When you run the project, PowerBuilder checks that:

• All public attributes and methods in the existing IDL interface are defined as public instance variables and functions in the user object.

• No methods defined in the IDL interface are overloaded in the user object.

If one of these checks fails, the component is deployed but a warning displays in the Project painter and the Output window.

These checks are performed only if the component is deployed using the project that was created when the component was created. If you create a new project or add the component to another project, no checks are performed when you run the project.

When you deploy using the project created with the component, the new implementation always uses the existing IDL on the server. You should be cautious if you use a different project, because you will be able to deploy the component to the original package and overwrite the existing IDL without seeing any warnings about changes in the interface.