EJB

EJB is the component architecture for the development and deployment of robust.

It is world class component-based distributed application using the java language. The EJB is a complex topic and requires a lot of effort to master it.

EJB 3.0 is framework that facilitate productive development of distributed an application can be broadly divided in to two parts.

1. Application logic and Data that is to be distributed.
2. System level services such as object management. State management or transaction management, persistence etc. Which are required to expose business logic an application data as distributed component. In an EJB application , The application developer focus, only one define business logic and data in such a way that they can be expose as an distributed component by EJB container.

The Enterprise JavaBeans (EJB) 3.0 specification defines an architecture for the development and deployment of transactional. It's a distributed object applications-based and also it's a server-side software components. The Organizations can build their own components or purchase components from third-party vendors.

These server-side components, called enterprise beans, are distributed objects that are hosted in Enterprise JavaBean containers and provide remote services for clients distributed throughout the network.

The Enterprise JavaBeans specification defines an architecture for a transactional, distributed object system based on components. The specification mandates a programming model; that is, conventions or protocols and a set of classes and interfaces which make up the EJB API.

The EJB programming model provides bean developers and EJB server vendors with a set of contracts that defines a common platform for development. The goal of these contracts is to ensure portability across vendors while supporting a rich set of functionality.

EJB as a technology contains in two things-

1. An API's Which as used to an application programming to define business logic and application data.
2. A runtime environment called EJB container which provide system level services.

Enterprise JavaBeans are server-side, modular, and it is using to reusable components that comprise specific units of functionality. They are similar to the Java classes we create every day EJB , but are subject to special restrictions and must provide specific interfaces for container and client use and access.

In addition, they can only run properly in an EJB container, which manages and invokes specific life cycle behavior. You should consider using EJB components when the application design requires scalability, transactional processing, or availability to multiple client types.

Most Probably EJB have components come in three varieties, each with its own defined role and life cycle:

1. Session beans:These may be either statefull or stateless, and are primarily used to encapsulate business logic, carry out tasks on behalf of a client, and act as controllers or managers for other beans.
2. Entity beans:Entity beans represent persistent objects or business concepts that exist beyond a specific application's lifetime; they are typically stored in a relational database. Entity beans can be developed using bean-managed persistence, which is implemented by the developer, or container-managed persistence, implemented by the container.
3. Message-driven beans: Message-driven beans listen asynchronously for Java Message Service (JMS) messages from any client or component and are used for loosely coupled, typically batch-type, processing.