Chapter 1: Creating Component-Based Applications

Implementing components and clients

With the design in place, your component developers and client developers can begin implementing the clients and components that form the application.

Implementing components

To create a Java-CORBA or EJB component, use a Java development tool to create the Java component. You can perform deployment tasks with EAServer Manager, jagtool, or jagant.

To create a C or C++ component, generate skeletons using EAServer Manager, code the method bodies in the method implementation templates, and compile and install the C DLL in your EAServer installation.

To create an ActiveX component, use an ActiveX-enabled IDE to create the ActiveX component DLL, import the ActiveX definitions for the component into EAServer, and install the ActiveX component.

To create a PowerBuilder component, use the EAServer Component wizard in PowerBuilder to define the interface, code the component in PowerScript, and deploy to EAServer.

To learn how to develop components, see these references:

Type of component	Chapter
EJB	Chapter 7, “Creating Enterprise JavaBeans Components”
Java-CORBA	Chapter 11, “Creating CORBA Java Components”
CORBA C++	Chapter 14, “Creating CORBA C++ Components”
PowerBuilder	The Application Techniques manual included in the PowerBuilder documentation.
ActiveX	Chapter 19, “Creating ActiveX Components”
C	Appendix C, “Creating C Components”

Design and implement the clients

Client developers can work concurrently with component developers. To allow prototyping and testing of client programs, you may want to create a client test server that hosts stubbed versions of the application components (that is, components with minimal method implementations).

Choose Client Types Before creating client programs, decide which of the following EAServer client models best suits your needs, based on your preferred implementation languages and administrative requirements:

Web applications You can invoke components from Java servlets and JavaServer Pages (JSPs) in a Web application. This approach allows the user interface to run anywhere a Web browser is installed. However, complex user interfaces with a high degree of interaction are difficult to implement.
Java Java applets do not require customer installation and simplify the task of providing upgrades. The customer always downloads the most recent applet. Applets require that the customer’s browser support JDK 1.2 or later.

If the client application is large and requires many Java classes, download time might be unacceptable. In this case, use a Java application that is installed locally on the client machine. This approach is ideal for intranet customers or even regular Internet customers. Although not as simple as providing upgrades with an applet, Java applications are no more difficult to upgrade than conventional software.

For Java development, you can use an IDE such as Borland JBuilder with the EAServer plugin. You can also use Jakarta Ant with jagtool tasks, as described in Chapter 12, “Using jagtool and jagant,” in the EAServer System Administration Guide.
PowerBuilder PowerBuilder is a Rapid Application Development (RAD) environment that supports drag-and-drop user interface generation. You can implement PowerBuilder clients that execute EAServer component methods using NVO proxies generated within PowerBuilder. As with C++ clients, the PowerBuilder runtime files must be distributed to each client workstation.
C++ C++ clients offer the proven performance of a native compiled executable. Some developers may prefer C++ user-interface generators such as Microsoft Visual C++. Finally, your company may have a large investment in existing C++ user-interface classes. C++ clients do require installation by the customer, however.
ActiveX If you are more familiar developing applications with an ActiveX-enabled IDE rather than Java, you can create an ActiveX client. An ActiveX client requires the same runtime installation as a C++ client, plus an additional step to register EAServer’s client proxy ActiveX interfaces.
Methods As Stored Procedures (MASP) EAServer’s MASP interface allows component methods to be executed as if they were database stored procedures. Any front-end tool that can execute Adaptive Server Enterprise stored procedures can execute EAServer methods using the MASP interface.

In some situations, you might want to implement different versions of a client for different users. For example, you may implement a Web client version to allow new customers to connect over the Internet without installing a client program. For established customers who use the application heavily, you can implement a standalone client program that offers improved performance and a richer user interface.

To learn how to create clients, see these references:

Type of client	Chapter
Java	Chapter 8, “Creating Enterprise JavaBeans Clients” Chapter 12, “Creating CORBA Java Clients”
C++	Chapter 15, “Creating CORBA C++ Clients”
PowerBuilder	The Application Techniques manual included in the PowerBuilder documentation.
ActiveX	Chapter 20, “Creating ActiveX Clients”
MASP	Appendix A, “Executing Methods As Stored Procedures”

Client Design Issues In designing your client, plan to optimize network performance by keeping traffic between the client and components on the server to a minimum. To optimize network performance, plan to:

Cache property changes in client data structures.
Validate field values on the client.
Update only the rows and columns that have changed. For example, do not implement a Java client to update an entire table when only a few rows have changed.
Group data changes into larger sets with fewer method calls.

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