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
- Management of transactions
- Pooling objects
Types of Beans
There are three categories of EJB:
- Session Bean
- Message Driven Bean
- Entity 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.
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.
Enterprise Java Beans: When to Use Them
- needs for applications Remote entry
- The application must be expandable.
- The Application requires business logic that is contained.
Enterprise Java Beans' benefits
- Enterprise beans receive system-level services from the EJB repository, allowing bean developers to concentrate on finding solutions to practical business issues. The EJB repository, not the bean developer, is in charge of system-level operations including transaction management and security authorisation.
- The client developer can focus on the client's interface since the business logic of the application is located in the beans rather than the clients. The client developer is not required to write the code for the pattern that accesses databases or executes business rules. As a result, the clients are slimmer, which is a feature that is crucial for clients that operate on small devices.
- The application assembler can create new apps from pre-existing enterprise Java beans because they are portable components.
Enterprise Java Beans' drawbacks:
- The application server is necessary
- Requires only java client. For another language client, you need to go for a web service.
- EJB application development is challenging.