Chapter 3 Creating J2EE Applications for Sybase EAServer

Enterprise JavaBean

Enterprise JavaBean (EJB) is a component model for Java.

There are several types of EJBs: Entity Bean, Session Bean, and Message Driven Bean.

Entity Bean is used for persistent objects. There are two types of persistence management: Container Managed Persistence (CMP) and Bean Managed Persistence (BMP). In CMP mode, the application server handles persistence. An EJB deployer has to define the O/R mapping information to allow the application server to know how to manage the persistence. In BMP mode, the persistence management code is defined in the EJB implementation class.

J2EE 1.3 has a new EJB 2.0 component model. The EJB 2.0 specification introduces a number of improvements: better definition for CMP, local interfaces, EJB Query Language (EJB-QL) and ejbSelect methods.

PowerDesigner supports UML object modeling and data modeling. It is interesting for customers to use the same tool to define objects, database schema, O/R mapping and to generate EJBs. PowerDesigner supports O/R mapping definition and EJB generation. It fully supports the EJB 2.0 specification. It can support any application server supporting EJB 2.0.

With PowerDesigner, you can:

• Define EJBs using the UML Class Diagram and Component Diagram
• Generate or reverse engineer a database using the Physical Data Model (PDM)
• Define O/R mapping
• Create CMP EJBs, BMP EJBs, Session Beans and Message Driven Beans
• Generate EJB source code, deployment descriptor
• Generate application server specific descriptor
• Compile Java code and generate the EJB JAR file
• Run the J2EE verifier
• Deploy EJBs into an application server
• Customize the EJB code generator and the application server support

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