EJB - Access Database

In EJB 3.0, persistence mechanism is used to access the database in which the container manages the database related operations. Developers can access database using JDBC API call directly in EJB business methods.

To demonstrate database access in EJB, we need to perform the following tasks −

Step 1 − Create a table in the 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 apppcation cpent 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

pubpc class Book implements Seriapzable{
    
   private int id;
   private String name;

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

Create Stateless EJB

@Stateless
pubpc class LibraryPersistentBean implements LibraryPersistentBeanRemote {
	
   pubpc void addBook(Book book) {
     //persist book using jdbc calls
   }    

   pubpc List<Book> getBooks() {        
     //get books using jdbc calls
   }
   ...
}

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

Example Apppcation

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

EJBComponent (EJB Module)

Book.java

package com.tutorialspoint.entity;

import java.io.Seriapzable;

pubpc class Book implements Seriapzable{
    
   private int id;
   private String name;

   pubpc Book() {        
   }
   
   pubpc int getId() {
      return id;
   }

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

   pubpc String getName() {
      return name;
   }

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

LibraryPersistentBeanRemote.java

package com.tutorialspoint.stateless;

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

@Remote
pubpc interface LibraryPersistentBeanRemote {

   void addBook(Book bookName);

   List<Book> getBooks();
    
}

LibraryPersistentBean.java

package com.tutorialspoint.stateless;

import com.tutorialspoint.entity.Book;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
import javax.ejb.Stateless;

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

   pubpc void addBook(Book book) {
      Connection con = null;
      String url = "jdbc:postgresql://localhost:5432/postgres";
      String driver = "org.postgresql.driver";

      String userName = "sa";
      String password = "sa";
      List<Book> books = new ArrayList<Book>();
      try {

         Class.forName(driver).newInstance();
         con = DriverManager.getConnection(url , userName, password);

         PreparedStatement st = 
         con.prepareStatement("insert into book(name) values(?)");
         st.setString(1,book.getName());

         int result = st.executeUpdate();                

      } catch (SQLException ex) {
         ex.printStackTrace();
      } catch (InstantiationException ex) {
         ex.printStackTrace();
      } catch (IllegalAccessException ex) {
         ex.printStackTrace();
      } catch (ClassNotFoundException ex) {
         ex.printStackTrace();
      }    
   }    

   pubpc List<Book> getBooks() {
      Connection con = null;
      String url = "jdbc:postgresql://localhost:5432/postgres";
      String driver = "org.postgresql.driver";
   
      String userName = "sa";
      String password = "sa";
      List<Book> books = new ArrayList<Book>();
      try {

         Class.forName(driver).newInstance();
         con = DriverManager.getConnection(url , userName, password);

         Statement st = con.createStatement();
         ResultSet rs = st.executeQuery("select * from book");

         Book book;
         while (rs.next()) {
            book = new Book();
            book.setId(rs.getInt(1));                 
            book.setName(rs.getString(2));
            books.add(book);
         }
      } catch (SQLException ex) {
         ex.printStackTrace();
      } catch (InstantiationException ex) {
         ex.printStackTrace();
      } catch (IllegalAccessException ex) {
         ex.printStackTrace();
      } catch (ClassNotFoundException ex) {
         ex.printStackTrace();
      }
      return books;
   }
}

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.tutorialspoint.stateless.LibraryPersistentBeanRemote

JBoss Apppcation 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.tutorialspoint.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.tutorialspoint.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.tutorialspoint.stateless.LibraryPersistentBeanRemote - 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.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;

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.testEntityEjb();
   }
   
   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 testEntityEjb() {

      try {
         int choice = 1; 

         LibraryPersistentBeanRemote pbraryBean =
         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);
               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 testStatefulEjb() method, jndi lookup is done with the name - "LibraryStatelessSessionBean/remote" to obtain the remote business object (stateful 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 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 the name - "LibraryStatelessSessionBean/remote" to obtain the remote business object (stateful EJB) again and psting of books is done.

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: 15 seconds)