EJB - Embeddable Objects

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EJB 3.0 provides option to embed JAVA POJO (Plain Old Java Object) into an entity bean and allows to map column names with the methods of the embedded POJO class. A java POJO to be embedded must be annotated as @Embeddable.

@Embeddable
public class Publisher implements Serializable{
   private String name;
   private String address;
   ...
}

The above class can be embedded using @Embedded annotation.

@Entity
public class Book implements Serializable{
   private int id;
   private String name;
   private Publisher publisher;
   ...
   @Embedded
   @AttributeOverrides({
      @AttributeOverride(name = "name", 
                      column = @Column(name = "PUBLISHER")),
      @AttributeOverride(name = "address", 
                      column = @Column(name = "PUBLISHER_ADDRESS"))
   })
   public Publisher getPublisher() {
      return publisher;
   }
   ...
}

Example Application

Let us create a test EJB application to test embedded objects in EJB 3.0.

Step Description
1

Create a project with a name EjbComponent under a package com.howcodex.entity as explained in the EJB - Create Application chapter. Please use the project created in EJB - Persistence chapter as such for this chapter to understand embedded objects in EJB concepts.
2

Create Publisher.java under package com.howcodex.entity as explained in the EJB - Create Application chapter. Keep rest of the files unchanged.
3

Create Book.java under package com.howcodex.entity. Use EJB - Persistence chapter as reference. Keep rest of the files unchanged.
4

Clean and Build the application to make sure business logic is working as per the requirements.
5

Finally, deploy the application in the form of a jar file on JBoss Application Server. JBoss Application server will get started automatically if it is not started yet.
6

Now create the EJB client, a console based application in the same way as explained in the EJB - Create Application chapter under topic Create Client to access EJB.

Create/Alter Book Table

CREATE TABLE book (
   id     integer PRIMARY KEY,
   name   varchar(50)
);
Alter table book add publisher varchar(100);
Alter table book add publisher_address varchar(200);

EJBComponent (EJB Module)

Publisher.java

package com.howcodex.entity;

import java.io.Serializable;
import javax.persistence.Embeddable;

@Embeddable
public class Publisher implements Serializable{
    
   private String name;
   private String address;

   public Publisher() {}

   public Publisher(String name, String address) {
      this.name = name;
      this.address = address;
   }

   public String getName() {
      return name;
   }

   public void setName(String name) {
      this.name = name;
   }

   public String getAddress() {
      return address;
   }

   public void setAddress(String address) {
      this.address = address;
   }

   public String toString() {
      return name + "," + address;
   }    
}

Book.java

package com.howcodex.entity;

import com.howcodex.callback.BookCallbackListener;
import java.io.Serializable;

import javax.persistence.AttributeOverride;
import javax.persistence.AttributeOverrides;
import javax.persistence.Column;
import javax.persistence.Embedded;
import javax.persistence.Entity;
import javax.persistence.EntityListeners;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="book")
public class Book implements Serializable{

   private int id;
   private String name;
   private Publisher publisher;

   public Book() {        
   }

   @Id
   @GeneratedValue(strategy= GenerationType.IDENTITY)
   @Column(name="id")
   public int getId() {
      return id;
   }

   public void setId(int id) {
      this.id = id;
   }

   public String getName() {
      return name;
   }

   public void setName(String name) {
      this.name = name;
   }


   @Embedded
   @AttributeOverrides({
      @AttributeOverride(name = "name", 
         column = @Column(name = "PUBLISHER")),
      @AttributeOverride(name = "address", 
         column = @Column(name = "PUBLISHER_ADDRESS"))
   })
   public Publisher getPublisher() {
      return publisher;
   }

   public void setPublisher(Publisher publisher) {
      this.publisher = publisher;
   }    
}

LibraryPersistentBeanRemote.java

package com.howcodex.stateless;

import com.howcodex.entity.Book;
import java.util.List;
import javax.ejb.Remote;

@Remote
public interface LibraryPersistentBeanRemote {

   void addBook(Book bookName);

   List<Book> getBooks();
    
}

LibraryPersistentBean.java

package com.howcodex.stateless;

import com.howcodex.entity.Book;
import java.util.List;
import javax.ejb.Stateless;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

@Stateless
public class LibraryPersistentBean implements LibraryPersistentBeanRemote {
    
   public LibraryPersistentBean() {
   }

   @PersistenceContext(unitName="EjbComponentPU")
   private EntityManager entityManager;         

   public void addBook(Book book) {
      entityManager.persist(book);
   }    

   public List<Book> getBooks() {
      return entityManager.createQuery("From Book").getResultList();
   }
}

  • 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 − LibraryPersistentBean/remote.

  • We will be using this lookup string to get remote business object of type − com.howcodex.interceptor.LibraryPersistentBeanRemote

JBoss Application Server Log Output

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

   LibraryPersistentBean/remote - EJB3.x Default Remote Business Interface
   LibraryPersistentBean/remote-com.howcodex.interceptor.LibraryPersistentBeanRemote - EJB3.x Remote Business Interface
...

EJBTester (EJB Client)

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 initialize the InitialContext object of java naming service.

  • InitialContext object will be used to lookup stateless session bean.

EJBTester.java

package com.howcodex.test;
   
import com.howcodex.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;

public 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));
   }
   
   public static void main(String[] args) {

      EJBTester ejbTester = new EJBTester();

      ejbTester.testEmbeddedObjects();
   }
   
   private void showGUI() {
      System.out.println("**********************");
      System.out.println("Welcome to Book Store");
      System.out.println("**********************");
      System.out.print("Options \n1. Add Book\n2. Exit \nEnter Choice: ");
   }
   
   private void testEmbeddedObjects() {

      try {
         int choice = 1; 

         LibraryPersistentBeanRemote libraryBean = 
        (LibraryPersistentBeanRemote)
         ctx.lookup("LibraryPersistentBean/remote");

         while (choice != 2) {
            String bookName;
            String publisherName;
            String publisherAddress;
            showGUI();
            String strChoice = brConsoleReader.readLine();
            choice = Integer.parseInt(strChoice);
            if (choice == 1) {
               System.out.print("Enter book name: ");
               bookName = brConsoleReader.readLine();
               System.out.print("Enter publisher name: ");
               publisherName = brConsoleReader.readLine();
               System.out.print("Enter publisher address: ");
               publisherAddress = brConsoleReader.readLine();
               Book book = new Book();
               book.setName(bookName);
               book.setPublisher
              (new Publisher(publisherName,publisherAddress));

               libraryBean.addBook(book);          
            } else if (choice == 2) {
               break;
            }
         }

         List<Book> booksList = libraryBean.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());
            System.out.println("Publication: "+book.getPublisher());
            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 initialize the InitialContext object.

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

  • Then the user is shown a library 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 database.

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

Run Client to Access EJB

Locate EJBTester.java in project explorer. Right click 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 html5
Enter publisher name: SAMS
Enter publisher address: DELHI
**********************
Welcome to Book Store
**********************
Options 
1. Add Book
2. Exit 
Enter Choice: 2
Book(s) entered so far: 1
1. learn html5
Publication: SAMS,DELHI
BUILD SUCCESSFUL (total time: 21 seconds)
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