Difference between Interceptors and Callback methods in EJB3

[Ravi Kiran Va]

Hi ,


I the process of Learning EJB Interceptors . I came across

The interceptor method runs before any of the bean's business methods are invoked.

In essence , interceptors give you a way to add functionality to your business methods without modifying the methods' code. For example, you can use an interceptor to validate parameters before they're passed to a business method, or perform security checks at the time the business method is called.


As per my thinking these tasks can be achivied using @PostConstruct callback methods know .

so please tell me when to use Interceptors and Callback methods ??

[Jaikiran Pai]

The @PostConstruct gets invoked only at the bean construction. It's not invoked before every business method invocation. The interceptor methods (@AroundInvoke) allow you to provide hooks before every business method is invoked.

[Ravi Kiran Va]

Thanks that was a good explanation .
import javax.ejb.*;

@Stateless

public class HelloWorldBean implements HelloWorld {

  public void sayHello() {
    System.out.println("Hello!");
  }

  @AroundInvoke
public Object myInterceptor(InvocationContext ctx) throws Exception 
{
    System.out.println("checkPermission interceptor invoked");
      ctx.getMethod());
    }

} 

Can you please tell me

For example if i have Method Level Interceptor like this when exactly this Interceptor is executed actually ?

I mean after the execution of sayHello or Before sayHello

[Leonardo Carreira]

Hi Ravi Kiran Varre..

It's nice to see you..
as far as i know.. EJB interceptors is executed before method execution..
Perhaps you could change your code as followed :

 
@Interceptors(MyFirstInterceptor.class)
@Stateless
public class HelloWorldBean implements HelloWorld {

  public void sayHello() {
    System.out.println("Hello!");
  }
} 

 
public class MyFirstInterceptor {
   public Object myInterceptor(InvocationContext ctx) throws Exception {
      //do some tasks
      System.out.println(ctx.getMethod().getName() + " is executed");
   }
}   

Hope this help..
Please correct me if i'm wrong..

Thanks

[Ravi Kiran Va]

Thank you very much , you solved my another query also that is how to write a Seperate class for Interceptor .