This post will explain What is EJB?. EJB is an architecture that is used to share software components among numerous customers. You may create and deploy programmes across all platforms using its robust server-side capabilities. You can learn more about EJB in this tutorial, including its many types, client access methods, lifecycles of various EJB, constructing EJB, packaging EJB, and mapping EJB with references.
What is EJB?
In this article, you can know about What is EJB? here are the details below;
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What Is EJB?
Enterprise JavaBeans are abbreviated as EJB.
It is based on JavaBeans technology and is a component of the J2EE platform.
A server-client approach is used by EJB, a server-side platform.
This platform offers the software building blocks needed to create distributed and reliable business applications.
The majority of the software’s components are written in Java.
EJBs, Java application servers, and EJB containers make up the three parts of the EJB architecture.
A runtime environment where EJB applications can be run is all that the EJB container is in this case.
The business logic of applications is primarily the emphasis of EJB.
The basic functionality of an application is represented by business logic.
Large-scale commercial applications can be made simpler with EJB.
Also, you may easily create and implement extremely scalable and high-performance applications.
Are you interested in learning why EJB is one of the effective frameworks for creating complex Java applications?
The following information will be useful to you in this regard:
- While leveraging EJB software components, clients can operate on compact devices without issue.
- Portable EJB.
- EJB can therefore be used on any J2EE server.
- System-level services are offered by the EJB container.
- Hence, in EJB apps, you can easily manage transaction management and security authorisation.
- By successfully managing the business logic of applications, EJB assists in resolving business issues.
- Scalability of EJB
- Hence, the number of machines running EJB can be effortlessly increased.
- Data integrity is ensured by EJB.
- It enables parallel access to shared objects.
- EJB can be instantly found by remote clients.
What Are the Types EJB?
Understand that there are three different sorts of EJB, as listed below:
Beans that are message-driven.
Let’s prepare to examine the various varieties of beans and their characteristics in the parts that follow.
Session beans are what?
You can create interactive sessions with clients by utilising session beans.
After the clients leave, the interactive sessions come to an end.
Session beans essentially offer online services and carry out activities for clients.
Session beans come in two varieties: stateful and stateless.
Let’s take a quick look at them as follows:
What are session Beans?
In other words, they keep track of many calls, all session bean-to-client interactions, and the conversational state.
Remember that every instance of a stateful session bean will have a unique identification.
And the EJB container assigns this identity while creating an instance.
The instance variables in this type represent the status of a session bean.
Stateless Beans: In contrast to stateful beans, stateless beans do not keep track of session data.
In other words, they don’t maintain a conversational state.
Stateless bean instances will all share a unique identifier.
In this kind, the instance variables retain the session’s state until the end.
The state of the session won’t be preserved after it is done.
It implies that all session beans have the same condition when there is no session.
The EJB container can issue session bean instances to any client without worrying about the beans’ current state.
Scalability is good with stateless beans.
They can therefore accommodate any quantity of customers.
Stateless beans perform better than stateful beans as a result.
Stateful beans are written in secondary storage, as opposed to stateless beans, which are not.
It makes sense that only a stateless bean could offer web services.
Configuring the EJB Components is a great resource.
How to create the Enterprise bean?
2. What are Entity Beans?
Entity beans are representations of business entity objects kept in a persistent storage system, such as a relational database.
Customers, goods, orders, etc. may make up the company entity.
Be aware that entity beans offer a wide range of characteristics, including shared access, main keys, persistence, and relationships with other beans.
Let’s talk about the following features:
Entity Bean adheres to persistence.
It implies that a bean’s state is retained long after an application has ended.
Entity beans adhere to two different types of persistence.
One is bean-managed persistence, and another is container-managed persistence.
You must incorporate calls to databases in your code in order to use bean-managed persistence.
EJB containers automatically add calls in codes for container-managed persistence, so you don’t need to do it. Also check Six Sigma Tools.
Shared Access: Entity beans can be shared among many clients.
Yet, because clients might modify data, they must work within transactions.
EJB containers control the transactions in this respect.
Recognize that each entity bean is given a special object identifier.
This identification is nothing more than a primary key.
A primary key enables a client to rapidly find an entity bean in the application server.
A customer number, for instance, might be used as a primary key to find a customer object.
Relationships: Every entity bean has a relationship with every other entity bean.
Bean-managed connections and container-managed relationships are two different kinds of relationships that EJB supports.
Bean-managed interactions rely heavily on codes, while container-managed relationships rely heavily on EJB containers.
3. What are Message-driven Beans?
- It makes sense that a single message-driven bean can handle many messages from various clients.
- The messages could be JMS or any other type of message.
- In this context, JMS is merely an API that facilitates communication between multiple application components.
- You can create, receive, transmit, and read messages using it as middleware.
- Moreover, JMS messages can be forwarded to Enterprise beans, web components, and application clients without any issues.
- While neither message-driven beans nor stateless beans maintain the state of their bean instances at any given time, they are somewhat comparable.
- Above all, message-driven beans support asynchronous Java programme execution.
What are the Different Client-Access methods used in EJB with interfaces?
- There is no denying that any kind of client can always access Enterprise Beans.
- The client could be a local, web service, or distant client.
- Clients can access entity beans and session beans by using interfaces.
- Message-driven beans, on the other hand, cannot be accessible using interfaces.
- Moreover, EJB only permits client access through the interface-defined methods.
- EJB employs three different types of client access techniques: local, web service, and remote.
- Considerations for local or remote access include container-managed connections, the degree of coupling between related beans, component distribution, client types, and performance.
- Remote Clients: A remote client could be a programme or a web component.
- It’s possible that it’s another Enterprise bean, which is not surprising.
- The remote client is unaware of the Enterprise bean’s location in this type.
- You must create codes for both the home interface and the remote interface in order to remotely access Enterprise beans.
- Remote interface outlines business practises.
- The home interface also specifies the lifecycle methods for the bean.
- Remember that business methods handle business operations like credit, deposit, etc., whereas lifecycle methods handle the create and delete actions.
- Local Clients: A local client can be a web component or any other Enterprise bean.
- Local clients and Enterprise Beans must both be located by the same JavaVirtualMachine (JVM).
- The location of an Enterprise bean is not transparent to local clients, in contrast to remote access.
- It is a good idea to have a backup plan in place in case something goes wrong.
- The local interface in this case defines the business methods of the bean, whereas the local home interface defines the lifecycle methods.
- Web service clients: There are two ways a web service can access Java applications.
- A web service built using JAX-RPC can be accessed by a client in one way or another.
- An XML-based remote procedure call is all that JAX-RPC is in this context.
- A stateless session bean’s business methods can also be swiftly called by a web service.
- A web service client, in contrast to remote and local clients, employs business-oriented interfaces.
- And the web service endpoint interface defines the business procedures.
- What Are the life Cycles of Different EJB?
- Whether it a session, message-driven, or entity Enterprise Bean, they all have various lifecycles.
Let’s talk about them below:
1. Life Cycle of a Stateful Session Bean
- By calling the “create” method, a client can start a stateful session bean’s lifecycle.
- The session bean’s setSessionContext function is raised by the EJB container once it has been instantiated.
- The ejbCreate method in the bean is then raised.
- The session bean is now prepared to support business methods.
- The EJB container has the option of activating or passivating the session bean when it enters the ready state.
- The EJB container raises the ejbPassivate method for passivation.
- The bean is transferred from memory to secondary storage during the passivation process.
- The EJB container enables the bean through the ejb Activate method when the client raises the business methods.
- The bean is then moved to a ready state by the EJB container.
- The client uses the delete method to terminate the session bean.
- When everything is finished, the EJB container invokes the ejbRemove function to end the session.
2. Life Cycle of a Stateless Session Bean
- In the lifecycle of a stateless session bean, there is no passivation stage.
- Only two phases make up a stateless session bean.
- The first stage is referred to as “non-existent,” and the second stage is referred to as “ready.”
- In most cases, the business techniques are brought up during the “ready” stage.
3. Life Cycle of an Entity Bean
- The EJB container creates an entity bean’s instance as the initial stage in the life cycle of an entity bean.
- The entity context is then transferred to the bean by the EJB container using the setEntityContext function.
- The bean then travels to the instance pool.
- Upon shifting the entity bean instance to the ready state, the EJB container constructs an identity for it.
- Entity beans can be transferred from the pooled state to the ready state utilising two methods.
- The EJB container raises the EJBCreate method after a client raises the create method, in one way.
- It then invokes the ejbPostCreate function.
- The ejbActivate method is also raised by the EJB container.
- As you are aware, customers can raise business strategies when beans are in the ready state.
- Entity Bean Life Cycle
- Beans can travel from a ready condition to a pooled state in two different ways.
- The EJB container calls the ejb Remove method once the client raises the remove method in one way.
- The client also invokes the ejbPassivate method.
- The unsetEntityContext method is raised at the conclusion of this lifecycle by the EJB container.
- The entity bean instances are then deleted from the pool.
4. Life Cycle of a Message-Driven Bean
- There are only two stages in the life cycle of a message-driven bean.
- One stage is “non-existent,” and another is “ready” to accept communications.
- The life cycle of a message-driven bean is not passivated, much like the life cycle of a stateless session bean.
- A collection of message-driven bean instances are produced by the EJB container during this lifespan.
- By using the setMessageDrivenContext function, the EJB container then gives the context object to each instance.
- The ejbCreate function is then invoked.
- At the conclusion of this lifecycle, the EJB container raises the ejb Uninstall method.
- A Message-Driven Bean’s Lifecycle
- Here, we’ll learn how to develop an Enterprise Bean called ConverterBean.
- The software programme used to convert currencies is called ConverterBean.
- Take into account that this bean is the stateless session bean.
- To construct the ConverterBean, you must perform the two steps listed below.
- The bean’s implementation class must be programmed.
- The source code must be compiled.
- Let’s explore how to do these two steps one at a time.
Step 1: Coding the Enterprise Bean Class
- The Enterprise Bean class used in this example is ConverterBean.
- The YenToEuro and DollerToYen currency conversions are supported by this class.
- And because it doesn’t implement a business interface, this class represents a no-interface and local view.
- Also, this class’s public methods are accessible to customers.
- The following is the source code for the Enterprise Bean class:
Step 2: Creating the converter Web Client
- Recognize that a Java Servlet is merely a web component that may react to HTTPS requests.
- The following Servlet class contains the web client.
- The ConverterServlet class often uses dependency injection to refer to the ConverterBean.
- When declaring a private member variable converter, the javax.ejb.EJB annotation is also used.
- As ConverterBean represents no-interface and a local view, Enterprise Bean implementation class is the variable type.
- The following codes can help you comprehend this.
- Making the Converter Web Client
- When you enter the amount converted from Yen to Euro or Dollar to Yen, the value is taken from the request parameters.
- The conversion will be carried out by calling methods like ConverterBean.
- YenToEuro and ConverterBean.
Step 3: Running the Converter
- At this point, you can compile the Enterprise Bean class and Servlet class.
- The compiled classes can then be packaged in a WAR file.
- You may create, package, run, and deploy the codes using either Maven or the NetBeans IDE.
- The steps listed below can be used if you want to run the scripts using the NetBeans IDE:
- Launch the GlassFish Server.
- Choose “Open Project” from the “File” menu.
- Choose the “Converter” folder.
- Then select “OpenProject.”
- Under the ‘Projects’ tab, right-click the ‘converter’ project.
- Choose “Build” now.
- Launch the Servlet Converter.
- Enter the number 100 in the field on the Servlet page.
- You can now retrieve the converted values by clicking “Submit.”
How to Package the Enterprise bean in the EJB JAR file?
You must launch the “edit Enterprise bean wizard” of the “deploy tool” application in order to package Enterprise Beans. The wizard will carry out the following tasks when you begin this process. The Enterprise Bean’s “deployment descriptor” is created by the wizard. It creates an EJB JAR file containing the Bean classes and the “deployment descriptor.”
The EJB JAR file is then added to ConverterApp.ear by the wizard. Let’s examine how the above-mentioned processes are used to package Enterprise Beans in the parts that follow. Start the “edit Enterprise Bean wizard” first. Then pick “file,” “new,” and “Enterprise Bean” from the menu. The wizard will now display the following dialogue windows, as you can see.
Introductory Dialog Box
You can read the wizard’s feature explanations in this dialogue box.
Next, press the “Next” button.
EJB JAR Dialog Box
- As a first step, click the “create new JAR Module” button in this dialogue box.
- Choose “ConverterApp” from the combo box below.
- In the JAR Display name field, type “ConverterJAR”
- You can now select the “Edit Contents” button.
- Find the build/converter subfolder in the tree under the accessible files.
- From the accessible files tree, you can choose classes like Converter.class, ConverterBean.class, and ConverterHome.class.
- Then, click “Add” and then “OK.”
- Lastly, press the “Next” button.
General Dialog Box
- You can first select the “stateless session” option under the Bean type in this generic dialogue box.
- Choose the converter next.
- ConverterBean in the Enterprise Bean Class combo box
- Enter ConverterBean in the Enterprise Bean Name field.
- Choose the converter next.
- ConverterHome is included in the Remote Home Interface combo box.
- Choose the converter.
- Converter in the Remote Interface combo box
- Hit the “Next” button.
- On the “Expose as Web Service Endpoint” dialogue box, select “No.”
- Click the “Next” and “Finish” buttons to finish.
How to Map the Enterprise bean References?
You must refer to the beans differently in your code depending on whether you’re accessing the same Enterprise Bean through a web client or an application client. Simply put, the web client refers to the bean’s home as ejb /TheConverter, whereas the application client refers to it as ejb /SimpleConverter. Also check Six Sigma Tools
You can use the lookup method to find the home bean if only the references in the codes are mapped to the JNDI names of the Enterprise Beans. The steps documented below can be used to map code references to JNDI names.
- First, select ConvertApp from the tree.
- Hit the’sun-specific settings’ option.
- Choose the JDNI names in the view field.
- Currently, you can see in the application table that ConverterBean is the JDNI name for the Enterprise bean.
- Then, for each row in the reference’s database, enter ConverterBean in the JNDI name field.
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What are the Advantages of EJB?
- When clients design and deploy Java applications using the EJB framework, there are many benefits.
- Here are some of them:
- Effectively managing EJB lifecycles, EJB containers offer system-level services.
- Several APIs, like JSPs and Servlets, are compatible with the EJB architecture.
- Business logic is the primary focus of EJB.
- Because of this, it creates large-scale applications and solves difficult business challenges quickly.
- It’s simple to pool EJB instances.
- On Java web application servers, EJB-based applications can execute.
- Portable EJB components
What are the Limitations of EJB?
- EJB does, without a doubt, have some restrictions.
- Here are some of them:
- Large and complex, the EJB specification
- An application server is necessary for EJB.
- EJB can only be used by Java clients.
- EJB development takes a little longer.
- Continuous revisions are released by EJB.
To put it briefly, EJB is the framework for offering software components (beans) for the creation of distributed and substantial enterprise applications. The business logic of an application serves as the foundation for EJB functions, which help developers create reliable Java applications.
Effective transaction management and security features in EJB applications are ensured by EJB’s system-level services. This tutorial examined enterprise beans’ numerous types, client access options, and lifecycles. It could have been easier to learn the EJB ideas in depth if there were more concrete examples of how to generate, package, and map enterprise beans.