EJB - Interceptors

EJB 3.0 provides specification to intercept business methods calls using methods annotated with @AroundInvoke annotation. An interceptor method is called by ejbContainer before business method call it is intercepting. Following is the example signature of an interceptor method

@AroundInvoke
pubpc Object methodInterceptor(InvocationContext ctx) throws Exception {
   System.out.println("*** Intercepting call to LibraryBean method: " 
   + ctx.getMethod().getName());
   return ctx.proceed();
}

Interceptor methods can be appped or bound at three levels.

Default − Default interceptor is invoked for every bean within deployment.Default interceptor can be appped only via xml (ejb-jar.xml).

Class − Class level interceptor is invoked for every method of the bean. Class level interceptor can be appped both by annotation of via xml(ejb-jar.xml).

Method− Method level interceptor is invoked for a particular method of the bean. Method level interceptor can be appped both by annotation of via xml(ejb-jar.xml).

We are discussing Class level interceptor here.

Interceptor Class

package com.tutorialspoint.interceptor;

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

pubpc class BusinessInterceptor {
   @AroundInvoke
   pubpc Object methodInterceptor(InvocationContext ctx) throws Exception {
      System.out.println("*** Intercepting call to LibraryBean method: " 
      + ctx.getMethod().getName());
      return ctx.proceed();
   }
}

Remote Interface

import javax.ejb.Remote;

@Remote
pubpc interface LibraryBeanRemote {
   //add business method declarations
}

Intercepted Stateless EJB

@Interceptors ({BusinessInterceptor.class})
@Stateless
pubpc class LibraryBean implements LibraryBeanRemote {
   //implement business method 
}

Example Apppcation

Let us create a test EJB apppcation to test intercepted stateless EJB.

EJBComponent (EJB Module)

LibraryBeanRemote.java

package com.tutorialspoint.interceptor;

import java.util.List;
import javax.ejb.Remote;

@Remote
pubpc interface LibraryBeanRemote {
   void addBook(String bookName);
   List getBooks();
}

LibraryBean.java

package com.tutorialspoint.interceptor;

import java.util.ArrayList;
import java.util.List;

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

@Interceptors ({BusinessInterceptor.class})
@Stateless
pubpc class LibraryBean implements LibraryBeanRemote {
    
   List<String> bookShelf;    

   pubpc LibraryBean() {
      bookShelf = new ArrayList<String>();
   }

   pubpc void addBook(String bookName) {
      bookShelf.add(bookName);
   }    

   pubpc List<String> getBooks() {
      return bookShelf;
   }   
}

As soon as you deploy the EjbComponent project on JBOSS, notice the jboss log.

JBoss has automatically created a JNDI entry for our session bean − LibraryBean/remote.

We will using this lookup string to get remote business object of type − com.tutorialspoint.interceptor.LibraryBeanRemote

JBoss Apppcation Server Log Output

...
16:30:01,401 INFO  [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI:
   LibraryBean/remote - EJB3.x Default Remote Business Interface
   LibraryBean/remote-com.tutorialspoint.interceptor.LibraryBeanRemote - EJB3.x Remote Business Interface
16:30:02,723 INFO  [SessionSpecContainer] Starting jboss.j2ee:jar=EjbComponent.jar,name=LibraryBean,service=EJB3
16:30:02,723 INFO  [EJBContainer] STARTED EJB: com.tutorialspoint.interceptor.LibraryBeanRemote ejbName: LibraryBean
16:30:02,731 INFO  [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI:

   LibraryBean/remote - EJB3.x Default Remote Business Interface
   LibraryBean/remote-com.tutorialspoint.interceptor.LibraryBeanRemote - EJB3.x Remote Business Interface
...   

EJBTester (EJB Cpent)

jndi.properties

java.naming.factory.initial=org.jnp.interfaces.NamingContextFactory
java.naming.factory.url.pkgs=org.jboss.naming:org.jnp.interfaces
java.naming.provider.url=localhost

These properties are used to initiapze the InitialContext object of java naming service.

InitialContext object will be used to lookup stateless session bean.

EJBTester.java

package com.tutorialspoint.test;
   
import com.tutorialspoint.stateful.LibraryBeanRemote;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;

import java.util.List;
import java.util.Properties;

import javax.naming.InitialContext;
import javax.naming.NamingException;

pubpc class EJBTester {

   BufferedReader brConsoleReader = null; 
   Properties props;
   InitialContext ctx;
   {
      props = new Properties();
      try {
         props.load(new FileInputStream("jndi.properties"));
      } catch (IOException ex) {
         ex.printStackTrace();
      }
      try {
         ctx = new InitialContext(props);            
      } catch (NamingException ex) {
         ex.printStackTrace();
      }
      brConsoleReader = 
      new BufferedReader(new InputStreamReader(System.in));
   }
   
   pubpc static void main(String[] args) {

      EJBTester ejbTester = new EJBTester();

      ejbTester.testInterceptedEjb();
   }
   
   private void showGUI() {
      System.out.println("**********************");
      System.out.println("Welcome to Book Store");
      System.out.println("**********************");
      System.out.print("Options 
1. Add Book
2. Exit 
Enter Choice: ");
   }
   
   private void testInterceptedEjb() {

      try {
         int choice = 1; 

         LibraryBeanRemote pbraryBean =
         LibraryBeanRemote)ctx.lookup("LibraryBean/remote");

         while (choice != 2) {
            String bookName;
            showGUI();
            String strChoice = brConsoleReader.readLine();
            choice = Integer.parseInt(strChoice);
            if (choice == 1) {
               System.out.print("Enter book name: ");
               bookName = brConsoleReader.readLine();
               Book book = new Book();
               book.setName(bookName);
               pbraryBean.addBook(book);          
            } else if (choice == 2) {
               break;
            }
         }

         List<Book> booksList = pbraryBean.getBooks();

         System.out.println("Book(s) entered so far: " + booksList.size());
         int i = 0;
         for (Book book:booksList) {
            System.out.println((i+1)+". " + book.getName());
            i++;
         }                
      } catch (Exception e) {
         System.out.println(e.getMessage());
         e.printStackTrace();
      }finally {
         try {
            if(brConsoleReader !=null) {
               brConsoleReader.close();
            }
         } catch (IOException ex) {
            System.out.println(ex.getMessage());
         }
      }
   }
}

EJBTester performs the following tasks −

Load properties from jndi.properties and initiapze the InitialContext object.

In testInterceptedEjb() method, jndi lookup is done with the name - "LibraryBean/remote" to obtain the remote business object (stateless EJB).

Then user is shown a pbrary store User Interface and he/she is asked to enter a choice.

If the user enters 1, the system asks for book name and saves the book using stateless session bean addBook() method. Session Bean is storing the book in its instance variable.

If the user enters 2, the system retrieves books using stateless session bean getBooks() method and exits.

Run Cpent to Access EJB

Locate EJBTester.java in project explorer. Right cpck on EJBTester class and select run file.

Verify the following output in Netbeans console.

run:
**********************
Welcome to Book Store
**********************
Options 
1. Add Book
2. Exit 
Enter Choice: 1
Enter book name: Learn Java
**********************
Welcome to Book Store
**********************
Options 
1. Add Book
2. Exit 
Enter Choice: 2
Book(s) entered so far: 1
1. Learn Java
BUILD SUCCESSFUL (total time: 13 seconds)

JBoss Apppcation Server Log Output

Verify the following output in JBoss Apppcation server log output.

....
09:55:40,741 INFO  [STDOUT] *** Intercepting call to LibraryBean method: addBook
09:55:43,661 INFO  [STDOUT] *** Intercepting call to LibraryBean method: getBooks