Enterprise Java Beans (EJBs) V2

The Java TM 2 Platform, Enterprise Edition (J2EE TM) is a Java platform that defines the standard for developing multi-tier enterprise applications. J2EE simplifies enterprise applications by basing them on standardized, reusable modular components, it provides a complete set of services to those components, and handles many details of application behavior automatically without complex programming.

Java 2 Enterprise Edition supports the following technologies that you can use in PowerDesigner:

Enterprise JavaBean (EJB)
Java Servlets (Servlets)
Java Server Page (JSP)

The following sections develop how to use these technologies in PowerDesigner.

EJB

Sun Microsystems definition of Enterprise JavaBeans TM is:

"The Enterprise JavaBeans architecture is a component architecture for the development and deployment of component-based distributed business applications. Applications written using the Enterprise JavaBeans architecture are scalable, transactional and multi-user secure. These applications may be written once and then deployed on any server platform that supports the Enterprise JavaBeans specification".

EJBs are non-visual, remotely executable components that can be deployed on a server, they provide a component architecture framework for creating distributed n-tier middleware. They communicate with clients to make some services available to them.

Enterprise JavaBeans enable rapid and simplified development of distributed, transactional, secure, and portable Java applications. EJB servers reduce the complexity of developing middleware by providing automatic support for middleware services such as transactions, security and database connectivity.

For more information on EJB, a specification is available from Sun Web site, at http://java.sun.com.

PowerDesigner supports the EJB 2.0 specification, with special emphasis on entity beans (both CMP and BMP). PowerDesigner implementation of EJB support can take full advantage of the tight integration between PDM and OOM.

What Do You Need to Work with EJBs?

You need Java 2 SDK Standard Edition (J2SE TM) 1.3 (final release), Java 2 SDK Enterprise Edition (J2EE TM) 1.3 (final release), a Java IDE or a text editor. You also need a J2EE application server supporting EJB 2.0.

It is also recommended that you set up the JAVA_HOME and J2EE_HOME system variables in your environment as follows:

In CLASSPATH:

%JAVA_HOME%\lib;%J2EE_HOME%\lib\j2ee.jar;%J2EE_HOME%\lib

In Path:

%JAVA_HOME%\bin;%J2EE_HOME%\bin

Using EJB Types
You can define the following types of EJB components:
EJB Properties
You can open the EJB page in the component property sheet to display the following properties:
Creating an EJB with the Wizard
You can create an EJB component with the wizard that will guide you through the creation of the component. It is only available if the language is Java.
Defining Interfaces and Classes for EJBs
An EJB comprises a number of specific interfaces and implementation classes. Interfaces of an EJB are always exposed, you define a public interface and expose it. You can attach an interface or class to only one EJB at a time.
Defining Operations for EJBs
You can create the following types of operations for an EJB from the property sheet of the Bean class or EJB interfaces:
Understanding EJB Support in an OOM
PowerDesigner simplifies the development process by transparently handling EJB concepts and enforcing the EJB programming contract through the following levels of support:
Using the EJB Deployment Descriptor
An EJB deployment descriptor describes the structure and properties of one or more EJBs in an XML file format. It is used for deploying the EJB in the application server. It declares the properties of EJBs, the relationships and the dependencies between EJBs. One deployment descriptor is automatically generated per package or model, it describes all EJBs defined in the package.
Generating EJBs
The EJB generation process allows you to generate EJB source code that is compliant with J2EE 1.3 (EJB 2.0). The code generator (Java, EJB, XML, etc...) is based on templates and macros. You can customize the generated code by editing the Java object language from Tools Resources Object Languages .
Generating JARs
In order to package the EJB, the bean classes, interfaces and the deployment descriptor are placed into a .JAR file. This process is common to all EJB components.
Reverse Engineering EJBs
You can reverse engineer EJB into an OOM for the Java language only. The reverse engineering feature processes .JAR files, Class or Java directories and reverses the deployment descriptor.

Parent topic: Working with Java