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Accelerate EJB 2.0 development with EJBGen

Simplify development and maintenance in your EJB CMP 2.0 model

By Thierry Janaudy, JavaWorld.com, 02/22/02

Developers who have worked with Enterprise JavaBeans (EJB) technology since its inception have experienced the hassle of the EJB development lifecycle. When I started to work with EJB 1.1 containers, I had to maintain classes and interfaces, usually using the Business Interface pattern to spot errors at compile time. I even had to manually create, edit, and maintain the XML deployment descriptors. In addition to being bug-prone, those steps usually delayed my development process.

Since then, the implementation of various projects has eased the EJB development process by automatically generating the deployment descriptors and remote, home, and local interfaces -- based on information provided by the bean class (that which implements javax.ejb.SessionBean or javax.ejb.EntityBean).

In this article, I will present EJB expert Cedric Beust's EJBGen tool. EJBGen limits your code editing to just one file, the bean class, which you annotate with javadoc tags. EJBGen, which is basically a doclet, parses your entity bean source file and generates the remote, home, and local interfaces for you.

EJBGen, doclet, and javadoc explained

As a Java developer, you certainly know javadoc, the JDK tool that lets you generate some HTML documentation based on comments you embed in your source code.

Javadoc uses the Doclet API to specify the content and format of its output. Sun Microsystems provides a default doclet that outputs HTML documentation. That doclet is composed of the classes in the com.sun.tools.doclets, com.sun.tools.doclets.standard, and com.sun.tools.doclets.standard.tags packages. The default doclet is used unless you select the javadoc's -doclet option. However, you can write your own doclet for enhanced functionality.

EJBGen is a doclet that outputs Java source code (local, remote, home interfaces) and XML deployment descriptors (ejb-jar.xml). In addition, EJBGen can generate proprietary deployment descriptors, weblogic-cmp-rdbms-jar.xml and weblogic-ejb-jar.xml, for BEA WebLogic 6.1.

EJBGen is easy to use because:

• You can quickly implement a large schema and entity bean relationships in just a few days
• You maintain just one class, the bean class
• You no longer manually maintain XML deployment descriptors

To show how to use EJBGen, I implemented an example from the EJB 2.0 specification, section 10.3.12: "An Order Entity Bean that Has Relationships with Line Items and Customers."

If you're new to EJB, I strongly suggest you read Chapter 10 of the EJB 2.0 specification: "Entity Bean Component Contract for Container-Managed Persistence."

Entity bean CMP 2.0

I don't intend to give you an in-depth presentation on entity beans; that would exceed the scope of this article. However, I would like to outline some of the many features and advantages that container-managed persistence (CMP) 2.0 can bring to your projects:

• An entity bean CMP class is small and maintainable
• The container generates the SQL code for persistence and finder queries, based on your portable EJBQL queries
• With a 2.0-compliant container, you can define relationships between entity beans (one-to-one, one-to-many, and many-to-many) and let the container manage these relations
• The container implements lazy loading techniques and other performance tricks
• You can focus on the business code, rather than the technical infrastructure
• You are not restricted to one vendor

Obviously, the EJB specification is not perfect. Some people were turned away by entity bean CMP in the EJB 1.1 specification, so they disregard it in EJB 2.0. However, if you're one of those people, you should reconsider your position and see how much this technology has improved.

 

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