Enterprise Java Beans

One of the many Java APIs for the common development of corporate software is Enterprise Java Beans (EJB). An EJB, a server-side software component, contains the business logic of an application. The Enterprise Java Beans web repository creates a runtime domain for web-related software elements including computer dependability, Java Servlet Lifecycle (JSL) management, transactional logic, and other web services. The Java EE enumeration is broken down into the EJB enumeration.

The EJB enumeration was initially created by IBM in 1997, and Sun Microsystems later accepted it and improved it as part of the Java Community Process.

A standard method of implementing the server-side business software often included in enterprise systems is provided by the EJB enumeration. Such machine code deals with the same issues, and programmers frequently re-implement solutions to these issues. Programmers are free to concentrate on the specific components of the enterprise software at hand because it is anticipated that Enterprise Java Beans will handle such common problems as endurance, transactional integrity, and security in a standard manner.

To run EJB applications, like Jboss, Glassfish, Weblogic, Websphere, etc., we need an application server (EJB Container). In doing so, it accomplishes the following:

management of the life cycle
Safety
Management of transactions
Pooling objects

Types of Beans

There are three categories of EJB:

Session Bean
Message Driven Bean
Entity Bean

Session Bean:

Business logic that may be accessed by local, remote, or web service clients is contained in the session bean. Session beans come in two varieties:

stateful session beans and
stateless session beans.

Stateful session bean:

Typically, stateful session beans store information about a particular client's session and keep it there during the entire session (as opposed to Stateless Session Beans). There is only one client attached to a Stateful EJB object. The number of EJB instances in a client's session is unlimited. And uses a state to help them carry out commercial tasks. By keeping the data in an instance variable, a stateful session bean may be utilised to access different method calls. Some applications need data to be stored across various method calls. The things a customer selects on a shopping site must be saved as data, an example of a stateful session bean.

Stateless Session bean:

An enterprise bean type that is typically utilised to carry out autonomous tasks is a stateless session bean. According to its name, a stateless session bean has no linked client state but may maintain its instance state. Typically, the EJB container constructs a small pool of stateless bean instances and uses those objects to handle client requests. Instance variable values across lookups and method calls are not always guaranteed due to the pool.

Message Driven Bean:

Enterprise beans that enable Java EE applications to handle messages asynchronously are known as message-driven beans. This type of bean often plays the part of a JMS message listener, which is similar to an event listener but receives JMS messages instead of events. Any Java EE component, including application clients, additional enterprise beans, and web components, as well as JMS systems and applications that don't use Java EE technology, may send the messages. JMS and other types of messages can be processed by message-driven beans.

Entity Bean:

It enumerates the possible states for the database. It has been retired. JPA has since taken its place (Java Persistent API). Entity beans come in two different flavours:

(i) Bean Managed Persistence :

The code for database calls must be written by the programmer in an entity bean with a bean-managed persistence type. It endures numerous sessions and clients.

(ii) Container Managed Persistence :

Enterprise beans with container-controlled persistence maintain their state across databases. Database calls are handled by the container in container controlled persistence.