Intercepting Method Invocations in EJB

Intercepting method invocations is a powerful feature provided by Enterprise JavaBeans (EJB). It allows you to add custom logic before, after, or around method executions in your EJB applications. This tutorial will guide you through the steps of intercepting method invocations in EJB and leveraging this feature to enhance your 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: Create an Interceptor Class

The first step is to create an interceptor class that implements the javax.interceptor.InvocationHandler interface. This interface provides a single method, invoke(), which is called when a method invocation is intercepted. Here's an example of a simple interceptor class that logs method invocations:


  import javax.interceptor.InvocationContext;

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

Step 2: Apply the Interceptor to EJB Methods

Once you have the interceptor class, you can apply it to specific EJB methods using the @Interceptors annotation. This annotation allows you to specify the interceptor class(es) to be applied. Here's an example of how to apply the LoggingInterceptor to an EJB method:


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

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

Common Mistakes

Forgetting to implement the InvocationHandler interface in the interceptor class.
Applying the interceptor to the wrong method or class.

Frequently Asked Questions

Q1: Can I apply multiple interceptors to a single method?

Yes, you can apply multiple interceptors to a single method by using the @Interceptors annotation and specifying multiple interceptor classes.

Q2: Can I intercept method invocations in a lifecycle callback method?

No, interceptors can only be applied to business methods in EJBs. They cannot intercept lifecycle callback methods.

Q3: Can I access the method parameters within an interceptor?

Yes, you can access the method parameters within an interceptor by using the InvocationContext object. It provides methods to retrieve method parameters and modify them if necessary.

Q4: Can I cancel or skip a method invocation from within an interceptor?

Yes, you can cancel or skip a method invocation by not calling the proceed() method of the InvocationContext object.

Q5: Can I apply interceptors to inherited methods?

Yes, interceptors can be applied to both inherited and non-inherited methods in EJBs.

Summary

Intercepting method invocations in EJB applications allows you to add custom behavior and logic to your methods. By following the steps outlined in this tutorial, you can create and apply interceptors to intercept method invocations in your EJBs. Remember to create the interceptor class, apply it using the @Interceptors annotation, and avoid common mistakes. Now you have the knowledge to leverage method invocation interception in your EJB applications and enhance their functionality!

Intercepting Method Invocations in EJB - Tutorial