EJB - Query Language

EJB Query Language is quite handy to write custom queries without worrying about underlying database details. It is quite similar to HQL, hibernate query language and is often referred by the name EJBQL.

To demonstrate EJBQL in EJB, we are going to do the following tasks −

• Step 1 − Create table in database.

• Step 2 − Create a stateless EJB having business me.

• Step 3 −Update stateless EJB. Add methods to add records and get records from database via entity manager.

• Step 4 − A console based application client will access the stateless EJB to persist data in database.

Create Table

Create a table books in default database postgres.

CREATE TABLE books (
   id     integer PRIMARY KEY,
   name   varchar(50)
);

Create a Model Class

public class Book implements Serializable{
    
   private int id;
   private String name;

   public Book() {        
   }
   
   public int getId() {
      return id;
   }
   ...
}

Create Stateless EJB

@Stateless
public class LibraryPersistentBean implements LibraryPersistentBeanRemote {
	
   public void addBook(Book book) {
     //persist book using entity manager
   }    

   public List<Book> getBooks() {        
     //get books using entity manager
   }
   ...
}

After building the EJB module, we need a client to access the stateless bean, which we will be going to create in the next section.

Example Application

Let us create a test EJB application to test EJB database access mechanism.

EJBComponent (EJB Module)

Book.java

package com.howcodex.entity;

import java.io.Serializable;

public class Book implements Serializable{
    
   private int id;
   private String name;

   public Book() {        
   }
   
   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;
   }    
}

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;
import javax.persistence.Query;

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

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

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

   public List<Book> getBooks() {
      //create an ejbql expression
      String ejbQL = "From Book b where b.name like ?1";
      //create query
      Query query = entityManager.createQuery(ejbQL);
      //substitute parameter.
      query.setParameter(1, "%test%");   
      //execute the query
      return query.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.stateless.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.stateless.LibraryPersistentBeanRemote - EJB3.x Remote Business Interface
16:30:02,723 INFO  [SessionSpecContainer] Starting jboss.j2ee:jar=EjbComponent.jar,name=LibraryPersistentBeanRemote,service=EJB3
16:30:02,723 INFO  [EJBContainer] STARTED EJB: com.howcodex.stateless.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.stateless.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.stateless.LibraryPersistentBeanRemote;
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.testEntityEjb();
   }
   
   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 testEntityEjb() {

      try {
         int choice = 1; 

         LibraryPersistentBeanRemote libraryBean =
         LibraryPersistentBeanRemote)
         ctx.lookup("LibraryPersistentBean/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);
               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());
            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 testStatefulEjb() method, jndi lookup is done with the name - "LibraryStatelessSessionBean/remote" to obtain the remote business object (stateful ejb).

• Then 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 persisting the book in database via EntityManager call.

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

• Then another jndi lookup is done with name - "LibraryStatelessSessionBean/remote" to obtain the remote business object (stateful EJB) again and listing of books is done.

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
BUILD SUCCESSFUL (total time: 15 seconds)