Ejb 简明教程

EJB - Embeddable Objects

EJB 3.0 提供将 JAVA POJO（纯老式 Java 对象）嵌入到实体 bean 中的选项，并允许将列名与嵌入式 POJO 类的对象进行映射。要嵌入的 java POJO 必须注释为 @Embeddable。

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

可以使用 @Embedded 注释来嵌入上述类。

@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;
   }
   ...
}

Example Application

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

Description

1

在包 com.tutorialspoint.entity 下创建一个名为 EjbComponent 的项目，如 EJB - 章节中所述。请使用在 EJB - 持久性章节中创建的项目，以便本章可以了解 EJB 概念中的嵌入对象。

2

在包 com.tutorialspoint.entity 下创建 Publisher.java，如 EJB - 章节中所述。保持其他文件不变。

3

在包 com.tutorialspoint.entity 下创建 Book.java。使用 EJB - 持久性章节作为参考。保持其他文件不变。

4

清理并构建应用程序以确保业务逻辑按需求工作。

5

最后，以 jar 文件的形式在 JBoss 应用程序服务器上部署应用程序。如果尚未启动 JBoss 应用程序服务器，它将自动启动。

6

现在创建 EJB 客户端，这是一个控制台应用程序，创建方法与 EJB - 章节中主题 Create Client to access EJB 下所述相同。

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();
   }
}

  1. 在 JBOSS 上部署 EjbComponent 项目后，请注意 jboss 日志。

  2. JBoss 已经为我们的会话 bean 自动创建了 JNDI 条目 - LibraryPersistentBean/remote 。

  3. 我们将使用这个查找字符串来获取类型为- com.tutorialspoint.interceptor.LibraryPersistentBeanRemote 的远程业务对象

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.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

  1. 这些属性被用于初始化java命名服务的InitialContext对象。

  2. InitialContext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 Book\n2. 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执行以下任务-

  1. 从jndi.properties加载属性并初始化InitialContext对象。

  2. 在testInterceptedEjb()方法中，jndi查找与名称“LibraryPersistenceBean/remote”相对应，用于获取远程业务对象（无状态EJB）。

  3. 然后向用户显示一个图书库用户界面，并询问他/她输入一个选择。

  4. 如果用户输入1，系统将询问图书名称，并使用无状态会话bean的addBook()方法保存图书。会话bean将图书存储到数据库中。

  5. 如果用户输入2，系统将使用无状态会话bean的getBooks()方法检索图书并退出。

Run Client to Access EJB

在项目浏览器中找到EJBTester.java。右键单击EJBTester类并选择 run file 。

在Netbeans控制台中验证以下输出。

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)