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Create forward-compatible beans in EJB, Part 1

How to write EJB 1.0 beans to port to EJB 1.1 servers

By Richard Monson-haefel, JavaWorld.com, 12/29/99

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Enterprise JavaBeans (EJB), which celebrated its one-year anniversary in June 1999, has been cutting its teeth on real-world applications. During EJB's first year, several areas of improvement were identified, many of which have been incorporated into EJB 1.1. These improvements include mandating support for entity beans, updating the deployment descriptors to an XML-based format, improving the bean-container contract, and tightening the overall specification to reduce ambiguities and loopholes.

Server-Side Java: Read the whole series!

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Although EJB 1.1 provides a more stable and concrete specification, it falters with some conventions in the EJB 1.0 programming model, introducing forward compatibility problems. Beans developed for the EJB 1.0-compliant server today will not automatically port to EJB 1.1 servers tomorrow. This article provides solutions for these problems. More information on additional changes from EJB 1.0 to EJB 1.1 can be found in Appendix D of my book Enterprise JavaBeans (O'Reilly, 1999), which is posted in HMTL and PDF formats at the O'Reilly Web site (see Resources).

This is the first of two installments about forward compatibility in Enterprise JavaBeans. This installment covers the environment-naming context and the implementation of an abstraction that hides the differences between EJB 1.0 and EJB 1.1 when accessing bean properties, Java Database Connectivity (JDBC), and other beans. The second installment addresses security, changes specific to entity beans, and changes to the deployment descriptor.

This is an advanced-topic article and is not intended for individuals new to Enterprise JavaBeans. Readers should be familiar with Java, Java Naming and Directory Interface (JNDI), JDBC, and the EJB 1.0 specification. In addition, I have simplified the exception handling so that the example code is clear and easy to follow. If you are not yet familiar with these technologies, be sure to see the Resources section for a review.

The environment-naming context

Enterprise JavaBeans 1.0 provides one interface to the bean's environment, the EJBContext. The EJBContext provides the bean class with an interface to the container, allowing the bean to discover and interact with aspects of its environment. The interface provides methods concerned with caller identity, transactions, and accessing environment properties.

Enterprise JavaBeans 1.1 introduces a new bean-container interface called the environment-naming context (ENC). The ENC is a JNDI name space that is specific to a bean type and its context at runtime. To simplify the bean-container interface, the ENC is made available, by default, when a JNDI context is created. The JNDI ENC enhances the bean-container contract by adding new functionality, but it doesn't completely replace the EJBContext. In EJB 1.1, the JNDI ENC and the EJBContext together represent the complete bean-container interface.

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