EJB嵌入对象详解

发布于 2015-06-07 09:10:56 | 207 次阅读 | 评论: 0 | 来源: 网友投递

EJB 3.0中提供了选项嵌入到实体bean的Java POJO（普通Java对象）和嵌入式POJO类的方法允许列名映射。嵌入一个java的POJO必须定义了@ Embeddable注解。


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

上面的类可以使用@ Embedded批注嵌入


@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;
   }
   ...
}

示例应用程序

让我们创建一个测试EJB应用程序来测试EJB 3.0中的嵌入对象。

Step	描述
1	Create a project with a name EjbComponent under a package com.tutorialspoint.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.tutorialspoint.entity as explained in the EJB - Create Application chapter. Keep rest of the files unchanged.
3	Create Book.java under package com.tutorialspoint.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 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 theEJB - 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.tutorialspoint.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.tutorialspoint.entity;

import com.tutorialspoint.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.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.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();
   }
}

一旦你部署EjbComponent项目在Jboss应用服务器，发现jboss的日志。
JBoss已经自动为我们的会话bean创建一个JNDI入口 - LibraryPersistentBean/remote.
我们将使用这个查询字符串来获得远程类型的业务对象 -com.tutorialspoint.interceptor.LibraryPersistentBeanRemote

JBoss应用服务器的日志输出


...
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.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.tutorialspoint.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.tutorialspoint.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

这些属性是用来初始化InitialContext对象的Java命名服务
InitialContext的对象将被用于查找无状态会话bean

EJBTester.java


package com.tutorialspoint.test;
   
import com.tutorialspoint.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 Bookn2. 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做以下任务。

jndi.properties中加载和初始化的InitialContext对象。
In testInterceptedEjb() method, jndi lookup is done with name - "LibraryPersistenceBean/remote" to obtain the remote business object (stateless ejb).
Then user is shown a library store User Interface and he/she is asked to enter choice.
If user enters 1, system asks for book name and saves the book using stateless session bean addBook() method. Session Bean is storing the book in database.
If user enters 2, system retrives books using stateless session bean getBooks() method and exits.

运行客户端访问EJB

在项目资源管理器中找到EJBTester.java。右键点击上EJBTester类，并选择 run file.

在Netbeans控制台验证以下输出。


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)