Using Interceptors in EJB

In Enterprise JavaBeans (EJB), interceptors are a powerful feature that allows you to enhance and customize the behavior of your applications. Interceptors can be used to intercept method invocations and perform additional tasks before, after, or around the method execution. This tutorial will guide you through the steps of using interceptors in EJB applications.

Prerequisites

Before you begin, make sure you have the following:

Basic understanding of EJB and Java EE
Java Development Kit (JDK) installed
Integrated Development Environment (IDE) for Java development

Step 1: Define the Interceptor Class

The first step is to create an interceptor class by implementing the javax.interceptor.InvocationContext interface. This class will contain the interception logic. Here's an example of a simple interceptor class that logs the method invocation:


  import javax.interceptor.AroundInvoke;
  import javax.interceptor.InvocationContext;

  public class LoggingInterceptor {
  
      @AroundInvoke
      public Object logMethodInvocation(InvocationContext context) throws Exception {
          System.out.println("Method " + context.getMethod().getName() + " called.");
          return context.proceed();
      }
  }

Step 2: Annotate EJB Methods with Interceptor

Once you have the interceptor class, you can apply it to EJB methods using the @Interceptor and @Interceptors annotations. Here's an example of how to apply the LoggingInterceptor to an EJB method:


  import javax.ejb.Stateless;
  import javax.interceptor.Interceptor;
  import javax.interceptor.Interceptors;

  @Stateless
  @Interceptors(LoggingInterceptor.class)
  public class MyEJB {
  
      public void doSomething() {
          // Method implementation
      }
  }

Common Mistakes

Forgetting to add the @Interceptor annotation to the interceptor class.
Applying the interceptor to the wrong target, such as a non-EJB class or method.

Frequently Asked Questions

Q1: Can I have multiple interceptors for a single EJB method?

Yes, you can apply multiple interceptors to a single EJB method by specifying them in the @Interceptors annotation.

Q2: Can I apply an interceptor to all methods in an EJB class?

Yes, you can apply an interceptor to all methods in an EJB class by adding the @Interceptors annotation at the class level.

Q3: Can interceptors modify the method parameters?

No, interceptors cannot modify the method parameters directly. They are intended for observation and manipulation of method invocations.

Q4: Can I control the order of interceptor execution?

Yes, you can specify the interceptor order using the @Priority annotation or by implementing the javax.annotation.Priority interface.

Q5: Can I apply interceptors to EJB lifecycle callback methods?

Yes, you can apply interceptors to EJB lifecycle callback methods by annotating them with the interceptor annotations.

Summary

Interceptors are a powerful feature in EJB that allow you to add custom logic to method invocations in your enterprise applications. By following the steps outlined in this tutorial, you can easily apply interceptors to your EJB methods and enhance their behavior. Remember to define your interceptor class, annotate EJB methods with the interceptor, and avoid common mistakes. Now you're ready to take advantage of interceptors in your EJB applications!

Using Interceptors in EJB - Tutorial