Architecture of EJB and its various types

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Short Answer

The architecture of EJB, or Enterprise JavaBeans, includes a few main parts: the EJB server, EJB containers, and the beans themselves.

There are three types of EJB:

  1. Session Beans: Handle business logic and can be stateful or stateless.
  2. Entity Beans: Represent data in a database.
  3. Message-Driven Beans: Deal with messages from other systems.

For example, a shopping cart might use a session bean to track your items, while entity beans represent the items in the store’s database.

Detailed Answer

The architecture of Enterprise JavaBeans (EJB) is designed to simplify the development of large-scale enterprise applications. It is a part of the Java EE platform and provides a framework for building modular components that can handle business logic, database interactions, and messaging.

EJB Architecture

  1. EJB Server: This is the application server that provides a runtime environment for EJBs. It manages system-level services like transactions, security, and threading.
  2. EJB Containers: These are part of the EJB server. They provide the environment where the beans run. Each bean gets its own container, which handles things like life cycle management and security.
  3. EJB Components: These are the beans themselves, which contain the business logic.

Types of EJB

  1. Session Beans: These are used to manage business processes. They come in two flavors:
    • Stateful Session Beans: Keep state information between method calls for a specific client.
    • Stateless Session Beans: Do not keep state information and can serve different clients with each method call.
  2. Entity Beans: These are now considered outdated and have been replaced by Java Persistence API (JPA). They were used to represent persistent data stored in a database.
  3. Message-Driven Beans: These beans allow asynchronous communication and can process messages sent by other applications or services.

For instance, in an online banking system, session beans might be used to handle user authentication and account transactions. Entity beans (or their modern JPA equivalents) would represent the customer’s account data. Message-driven beans could be used to process notifications or transactions received from external banking networks.

In conclusion, the EJB architecture is a robust framework for developing and deploying enterprise-level applications. It provides a scalable and secure environment for business logic, database operations, and message handling. The different types of EJBs offer specialized functionalities to cater to various aspects of application development.