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EJB Container Annotations

With J2EE Enterprise JavaBeans components can be developed ( enterprise beans) can then be reused and assembled into different applications that have to do for the company.
component-based development promises a step in the path of object-oriented programming. With programming you can reuse object-oriented classes, but you can reuse components n greater level of functionality and even these features can be modified and adapted to each particular work environment without touching the code of the component.
At this moment we see a component as a traditional object with a set of additional services supported at runtime by the container components. The container component called EJB container and is like the operating system in which they reside. Remember that in Java there is a programming model called RMI remote objects. With RMI you can send requests to objects running in another Java virtual machine. We can see an EJB component as an RMI remote object that resides in an EJB container that provides a set of additional services.

Services provided by the EJB container

• transaction management: opening and closing transactions associated with calls to the methods of the bean.
• Security: Check access permissions to the methods of the bean.
• attendance: simultaneous call to one bean from multiple clients.
• Network Services: Communication between the client and the bean on different machines.
• Resource Management: automatic management of multiple resources, such as message queues, databases or data sources in legacy applications that have not been translated into new languages \u200b\u200b/ environments and are still used in the company.
• Persistence: data synchronization between the bean and tables in a database.
• message management: Managing Java Message Service (JMS).
• Scalability: ability to form clusters of application servers with multiple hosts to respond to surges in application load by simply adding additional hosts. Adaptation
• deployment time: the possibility of modification all these characteristics at the time of deployment of the bean.

Performance of EJB components

The performance of EJB components is based primarily on the work of the EJB container. The EJB container is a Java program running on the server that contains all classes and objects necessary for the proper functioning of the enterprise beans.

In the figure below you can see a very high level representation of the basic operation of the enterprise beans. First, you can see that the client making requests to the bean and the server that contains the bean are running on different Java virtual machines. Even can be in different hosts. Another thing to note is that the client never communicates directly with the enterprise bean, but the EJB container provides a EJBObject to interface. Any request (a call to a business method enterprise bean) should be done through the EJB object, which calls the EJB container a number of services and communicates with the enterprise bean. Finally, the bean performs the requests for the database.

The EJB container is concerned with issues such as:

• Does the client have permission to call the method?
• should be open transaction at the beginning of the call and close it when finished.
• Is it necessary to refresh the bean with data from the database?

high-level representation of the operation of the enterprise beans.