Chapter 4 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 Beans are used for persistent objects. There are two types of persistence management:

• Container Managed Persistence (CMP) - 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.
• Bean Managed Persistence (BMP) - 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 useful for designers 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, including 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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