EJB Access數(shù)據(jù)庫

EJB 3.0 持久化機制是用來訪問數(shù)據(jù)庫中的容器管理數(shù)據(jù)庫相關(guān)的操作。開發(fā)人員可以訪問在EJB 業(yè)務(wù)方法中直接使用JDBC API調(diào)用數(shù)據(jù)庫。

為了證明在EJB的數(shù)據(jù)庫訪問，我們將執(zhí)行以下任務(wù)。

• 第1步：在數(shù)據(jù)庫中創(chuàng)建表。

• 第2步：創(chuàng)建具有業(yè)務(wù)我無狀態(tài) ejb。

• 第3步：更新無狀態(tài)EJB。添加的方法來添加記錄，并通過實體管理器獲得數(shù)據(jù)庫記錄。

• 第4步：基于控制臺應(yīng)用程序的客戶端將訪問無狀態(tài)EJB在數(shù)據(jù)庫中留存數(shù)據(jù)。

創(chuàng)建表

默認的數(shù)據(jù)庫Postgres中創(chuàng)建一個table books。

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

創(chuàng)建模型類

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

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

創(chuàng)建無狀態(tài)EJB

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

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

構(gòu)建EJB模塊之后，我們需要一個客戶端訪問無狀態(tài)bean，我們將會在下一節(jié)中創(chuàng)建。

示例應(yīng)用程序

讓我們創(chuàng)建一個測試EJB應(yīng)用程序來測試EJB的數(shù)據(jù)庫訪問機制。

EJBComponent（EJB模塊）

Book.java

package com.tutorialspoint.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.tutorialspoint.stateless;

import com.tutorialspoint.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.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
public class LibraryPersistentBean implements LibraryPersistentBeanRemote {
    
   public LibraryPersistentBean(){
   }

   public 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();
      }    
   }    

   public 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;
   }
}

• 一旦你部署EjbComponent項目到JBoss上，注意jboss的日志。

• JBoss已經(jīng)具備自動創(chuàng)建我們的會話bean JNDI入口- LibraryPersistentBean /remote。

• 我們將使用這個查詢字符串獲取遠程業(yè)務(wù)類型的對象- com.tutorialspoint.stateless.LibraryPersistentBeanRemote

JBoss應(yīng)用服務(wù)器日志輸出

...
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客戶端）

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

• 這些屬性是用來初始化java命名服務(wù)的InitialContext對象
  

• InitialContext對象將被用于查找無狀態(tài)會話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;

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 
1. Add Book
2. Exit 
Enter 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執(zhí)行以下任務(wù)。

• 從 jndi.properties 加載屬性并初始化InitialContext對象。

• 在testStatefulEjb()方法中,jndi查找名稱——“LibraryStatelessSessionBean /remote”來獲取遠程業(yè)務(wù)對象(有狀態(tài)的ejb)。

• 然后用戶顯示庫存儲用戶界面和他（她）被要求輸入選擇。

• 如果用戶輸入1，系統(tǒng)將要求書名稱并保存使用無狀態(tài)會話 bean addBook() 方法的書。會話 Bean 堅持通過實體管理器調(diào)用數(shù)據(jù)庫中的書。
  

• 如果用戶輸入2，系統(tǒng)retrives使用無狀態(tài)會話bean getBooks（）方法，并退出書籍。

• 然后另一個JNDI查找與名行 - “LibraryStatelessSessionBean /remote”，來獲取遠程業(yè)務(wù)對象(有狀態(tài)的ejb)和書的清單。

運行客戶端訪問EJB

在項目資源管理器中找到EJBTester.java。右鍵單擊EJBTester類并選擇 run file 運行文件 。

驗證以下在 Netbeans 控制臺輸出。

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)