How do you create a Java EE application using EJB?

Table of Contents

• Introduction
• Steps to Create a Java EE Application Using EJB
  • 1. Set Up the Development Environment
  • 2. Create a Maven Project
    • Example pom.xml for EJB:
  • 3. Create a Session Bean
    • Example: Stateless Session Bean
    • Example: Stateful Session Bean
  • 4. Create an EJB Client
    • Example: Calling the Stateless EJB from a Servlet
  • 5. Define a Transaction Management Strategy
    • Example: Managing Transactions in EJB
  • 6. Deploy and Run the Application
  • 7. Access EJB via a Web Interface (JSF or Servlet)
  • 8. Test and Debug
• Conclusion

Introduction

Java EE (Enterprise Edition) provides a robust platform for building enterprise-grade applications. One of its core components is Enterprise JavaBeans (EJB), which simplifies the development of business logic by providing built-in support for transactions, security, and concurrency. EJB enables developers to focus on writing business logic without worrying about underlying complexities like transaction management, persistence, and security.

In this guide, we'll walk you through the process of creating a simple Java EE application using EJB. You'll learn how to create different types of EJBs (Session Beans, Message-Driven Beans), configure them, and integrate them into your Java EE application.

Steps to Create a Java EE Application Using EJB

1. Set Up the Development Environment

Before you start coding, make sure you have the following tools set up:

• IDE: Use an Integrated Development Environment (IDE) such as Eclipse or IntelliJ IDEA, which support Java EE development and offer tools for creating and deploying Java EE applications.
• Java EE Server: Set up a Java EE-compliant application server such as WildFly, GlassFish, or Payara to deploy and run your application.
• JDK: Ensure you have the appropriate version of the Java Development Kit (JDK) installed (usually JDK 8 or above).

2. Create a Maven Project

In most Java EE applications, Maven is used to manage dependencies and build the application. You can create a Maven-based project in your IDE and add the necessary dependencies for EJB.

Example pom.xml for EJB:

This will include the necessary libraries for EJB and other Java EE components.

3. Create a Session Bean

In EJB, Session Beans are used to implement business logic. They can be stateful or stateless, depending on whether you need to maintain client-specific state between method calls.

Example: Stateless Session Bean

A Stateless Session Bean does not maintain any client-specific state between method calls. It is ideal for performing simple business operations that do not need to track client interactions.

In this example:

• The CalculatorBean is a Stateless EJB because it does not maintain any state between method calls.
• The @Stateless annotation defines this as an EJB bean.
• The Calculator interface defines the methods that will be implemented by the bean.

Example: Stateful Session Bean

A Stateful Session Bean can maintain the client's state across multiple method calls. This is useful if you need to track client-specific information during a conversation.

• The ShoppingCartBean is a Stateful EJB that tracks items in a shopping cart between method calls.

4. Create an EJB Client

Once you have your EJB components, you need a client to invoke them. In a Java EE application, clients can be EJBs, Servlets, JSF beans, or other types of Java EE components.

Example: Calling the Stateless EJB from a Servlet

• The @EJB annotation is used to inject the CalculatorBean (Stateless EJB) into the CalculatorServlet.
• The servlet can now call the business logic provided by the EJB.

5. Define a Transaction Management Strategy

Java EE provides built-in support for transaction management. In EJB, transactions are typically managed automatically, but you can also configure custom transaction attributes using the @TransactionAttribute annotation.

Example: Managing Transactions in EJB

• The @TransactionAttribute annotation specifies how transactions are handled. In this case, it requires a transaction to be active when the method is invoked.

6. Deploy and Run the Application

Once you've written your EJB components and configured them, the next step is to deploy the application to your Java EE application server.

• Use the Maven build process to package your application as a .war or .ear file.
• Deploy the package to the server (e.g., WildFly, GlassFish).
• Access the web pages (e.g., via Servlets or JSF) or test the EJB functionality through HTTP requests.

7. Access EJB via a Web Interface (JSF or Servlet)

You can access your EJB from the front-end of your application. For example, using JSF, you can call EJB methods and display results.

• Here, shoppingCartBean is a Stateful EJB injected into the JSF Managed Bean and used to track items in the shopping cart.

8. Test and Debug

After deployment, thoroughly test your application by checking the functionality of the EJB components, transaction management, and interaction with the client-side interface (e.g., JSF or Servlet). Utilize logging and debugging tools to track issues and ensure the application works as expected.

Conclusion

Creating a Java EE application using EJB allows you to build robust, scalable enterprise applications with minimal overhead. By leveraging the power of EJB, you can easily implement business logic, manage transactions, and integrate components like Servlets, JSF, and other Java EE technologies. The simplicity of EJBs, combined with the Java EE container's built-in features (like transaction management, security, and concurrency), makes it easier to focus on building business logic without worrying about low-level details.