EJB - Blobs/Clobs

EJB 3.0 provides support for Blob and Clob types using @Lob annotation. Following java types can be mapped using @Lob annotation.

• java.sql.Blob
• java.sql.Clob
• byte[]
• String
• Serializable Object

@Entity
@Table(name="books")
@EntityListeners(BookCallbackListener.class)
public class Book implements Serializable{
   ...
   private byte[] image;    

   @Lob @Basic(fetch= FetchType.EAGER)
   public byte[] getImage() {
      return image;
   }
   ...
}

Example Application

Let us create a test EJB application to test blob/clob support in EJB 3.0.

Create/Alter Book Table

CREATE TABLE book (
   id     integer PRIMARY KEY,
   name   varchar(50)
);
Alter table book add image bytea;
Alter table book add xml text;

EJBComponent (EJB Module)

Book.java

package com.howcodex.entity;

import com.howcodex.callback.BookCallbackListener;
import java.io.Serializable;
import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.EntityListeners;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Lob;
import javax.persistence.Table;

@Entity
@Table(name="book")
public class Book implements Serializable{
    
   private int id;
   private String name;    
   private byte[] image;   
   private String xml;

   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;
   }

   @Lob @Basic(fetch= FetchType.EAGER)
   public byte[] getImage() {
      return image;
   }

   public void setImage(byte[] image) {
      this.image = image;
   }

   @Lob @Basic(fetch= FetchType.EAGER)
   public String getXml() {
      return xml;
   }

   public void setXml(String xml) {
      this.xml = xml;
   }
}

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 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.testBlobClob();
   }
   
   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 testBlobClob() {

      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();
               String xml = "<book><name>"+bookName+"</name></book>";
               Book book = new Book();
               book.setName(bookName);                                        
               byte[] imageBytes = {0x32, 0x32,0x32, 0x32,0x32,
               0x32,0x32, 0x32,
               0x32, 0x32,0x32, 0x32,0x32, 0x32,0x32, 0x32,
               0x32, 0x32,0x32, 0x32,0x32, 0x32,0x32, 0x32
               };
               book.setImage(imageBytes);
               book.setXml(xml);

               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());
            byte[] imageByts = book.getImage();
            if(imageByts != null) {
               System.out.print("image bytes: [");
               for(int j = 0; j < imageByts.length ; j++) {
                  System.out.print("0x" 
                  + String.format("%x", imageByts[j]) +" ");
               }            
               System.out.println("]");
            }        
            System.out.println(book.getXml());
            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 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 testing
**********************
Welcome to Book Store
**********************
Options 
1. Add Book
2. Exit 
Enter Choice: 2
Book(s) entered so far: 1
1. learn testing
image bytes: [
   0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 ]
<book><name>learn testing</name></book>
BUILD SUCCESSFUL (total time: 20 seconds)