The journey of EJB Technology (i)

EJB Technology is now a selling point for many products, so it becomes important for developers to master this skill. EJB technology has not been born for a long time, in the domestic application has just started, there are a lot of this information, books, but there are such a few problems. First, there is no depth of content, such as the use of what tools to develop an EJB instance, step-by-step to teach the reader the specific application, this content for beginners to have some help. Second, the EJB technology is very good, why is it good? We all use it, and I think a lot of people ignore the internal mechanism of technology itself. Third, each technology area has its own core content, these materials do not teach readers how to face the new technology quickly cut into the core layer of methods, if the future appeared "Java 3"? And so on, these are the issues that we deserve to consider. In foreign countries, EJB technology used a lot, through the http://java.sun.com provided in the EJB mailing list content to know the level of others.

In fact, although the EJB technology is complex, difficult to learn, but there is a good way to learn, like UML, grasp the fundamental, regardless of the details of the part, this is the title of this article is the purpose!

Take these questions and start our EJB technology trip. I hope you have a pleasant journey.

Open question

The EJB technology, invented by Sun, has released 3 versions of EJB specifications since its invention, 1.0,1.1,2.0. EJB version 2.1 has released the proposed final draft (http://java.sun.com/products/ejb/, detailed address). The EJB specification defines the respective responsibilities of component developers and EJB server vendors. Component developers write EJBS based on the programming model defined in the EJB specification. EJBs that follow the EJB specification can be ported in each EJB server. Such a programming model provides an excellent convenience to EJB developers, and what is the background of EJB generation?

EJB technology absorbs the benefits of TP monitors and distributed-component services while discarding their shortcomings. TP monitors is a kind of running process language, such as COBOL, PL/1, written application reliable, powerful platform, the Platform management application environment, such as transactional, security, resource management, load balancing, fault tolerance and so on. So this platform advantage provides a good infrastructure for "mission-critical" Enterprise-class applications. At the same time, TP monitors adopts industry advanced 3-tier architecture, which consists of presentation layer, business logic layer and back-end resource. Distributed-component Services provides a more advanced 3-tier architecture, where business objects, components are placed in the middle tier, and other processes can access themselves through the Romote proxies they provide (familiar with CORBA, Java RMI, DCOM's friends, all know this).

The advantage of distributed components and loads over traditional TP monitors applications is that it provides greater reusability and flexibility because they can integrate different kinds of business objects, but such components are difficult to write and the lack of TP The robust infrastructure provided by monitors. If we can combine the advantages of the two, it will constitute the cause of the EJB emergence. The EJB server provides an environment similar to TP monitors for distributed components. In the EJB server, the monitors environment such as TP reduces the complexity of the development, and the distributed components makes the developer's development efficiency greatly improved.

EJB clients are accessed through Jndi, Java Rmi-iiop. Such customers may be Java applications, JSPs (Servlets), other EJBs, or applications written in other languages.

Sun's definition of EJB architecture:

"The Enterprise JavaBeans architecture is a component architecture for the development and deployment of componentbased di stributed business Applications. Applications written using the Enterprise JavaBeans architecture are scalable, transactional, and multi-user secure. These applications may are written once, and then deployed on no server platform that supports the Enterprise JavaBeans SP Ecification. "

Such a definition reflects that EJB is suitable for "mission-critical" enterprise applications.

Article Organization structure:

This series of articles is mainly based on the technology involved in the EJB 2.0 specification. Development tools recommend the use of JBuilder 7, the server itself random. I use WebLogic 7.0. Regarding the integration of both, it is advisable to look at the integration white Paper provided by Borland, the link address I gave in the previous article.

Each article will give an analysis of a key technology in the EJB, or a design example.