Describe EJB architecture

Briefly describe EJB architecture.

- The EJB architecture is an extension of Web architecture.

- It has an additional tier.

- The clients of an enterprise bean can be a traditional java application – an applet, a JSP or servlet.

- Like in a web application, client browser has to go all the way to web container to use a servlet or JSP, the communication between beans and clients is performed by the EJB container.

- The following are the flows of the EJB architecture.

1. The client is working on a web browser.
2. There is a database server that hosts a database, like MySQL / Oracle.
3. The J2EE server machine is running on an application server
4. The client interface is provided with JSP / Servlet. The enterprise beans reside in the business tier providing to the client tier.
5. The Application Server manages the relationships between the client and database machines.

Briefly describe EJB architecture.

- An enterprise bean is a non-visual component of a distributed, transaction-oriented enterprise application.

- Enterprise beans are typically deployed in EJB containers and run on EJB servers.

- Every EJB has three classes:

1. A home interface which acts as a factory of remote objects.
2. A remote object which is used for client interaction
3. A bean object which contains all the business logic

Remote client view :

- Its specification is available only in EJB 2.0 and an enterprise bean remote client view is location independent.

Remote interface :

- It specifies the remote business methods that a client can call on an enterprise bean.

- Remote home interface.

- It specifies the methods used by remote clients for locating, creating, and removing instances of the enterprise bean classes.

Local client view :

- Its specification is only available in EJB 2.0 and the local client view of a bean is location dependent, unlike the remote client view.

1. Local interface :

- It is a lightweight version of the remote interface, but for local clients.
- It includes business logic methods that can be called by a local client.

2. Local home interface :

- The local home interface specifies the methods used by local clients for locating, creating, and removing instances of enterprise bean classes.

EJB client JAR file :

- An EJB client JAR file is an optional JAR file that can contain all the class files that a client program needs to use the client view of the enterprise beans that are contained in the EJB JAR file.

- If you decide not to create a client JAR file for an EJB module, all of the client interface classes will be in the EJB JAR file.

EJB container :

- An EJB container is a run-time environment that manages one or more enterprise beans.

- It manages the life cycles of enterprise bean objects, coordinates distributed transactions and implements object security.

Deployment descriptor :

- A deployment descriptor is an XML file packaged with the enterprise beans in an EJB JAR file or an EAR file.

- It contains metadata describing the contents and structure of the enterprise beans, and runtime transaction and security information for the EJB container.

EJB server :

- An EJB server is a high-level process or application that provides a run-time environment to support the execution of server applications that use enterprise beans.

- An EJB server provides a JNDI-accessible naming service.

- It manages and coordinates the allocation of resources to client applications, provides access to system resources and provides a transaction service.
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Web technology
Plz give me ejb architecture
Rajesh 05-23-2018