EJB依赖注入

EJB 3.0规范提供了注释字段或setter方法注入依赖可以应用。 EJB容器使用的全局JNDI注册表定位的依赖。以下注解在EJB 3.0中使用依赖注入。

@EJB - 用来注入其他EJB引用。
@Resource - 用于注入数据源或单例服务，如sessionContext，timerService等

@EJB使用步骤

@EJB 可以使用栏位或以下方式的方法。

public class LibraryMessageBean implements MessageListener {
   //dependency injection on field. 
   @EJB
   LibraryPersistentBeanRemote libraryBean;
   ...
}

public class LibraryMessageBean implements MessageListener {
  
   LibraryPersistentBeanRemote libraryBean;
   
   //dependency injection on method. 
   @EJB(beanName="com.tutorialspoint.stateless.LibraryPersistentBean")
   public void setLibraryPersistentBean(
   LibraryPersistentBeanRemote libraryBean)
   {
      this.libraryBean = libraryBean;
   }
   ...
}

@Resource 使用步骤

@Resource 通常用于注入EJB容器提供单例。

public class LibraryMessageBean implements MessageListener {
   @Resource
   private MessageDrivenContext mdctx;  
   ...
}

示例应用程序

让我们创建一个测试EJB应用程序来测试EJB服务的依赖注入。

Step	Description
1	Create a project with a name EjbComponent under a package com.tutorialspoint.timer as explained in the EJB - Create Application chapter.
3	Use Beans created in the EJB - Message Driven Bean chapter. Keep rest of the files unchanged.
5	Clean and Build the application to make sure business logic is working as per the requirements.
6	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.
7	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.

EJBComponent (EJB Module)

LibraryMessageBean.java

package com.tuturialspoint.messagebean;
 
import com.tutorialspoint.entity.Book;
import com.tutorialspoint.stateless.LibraryPersistentBeanRemote;
import javax.annotation.Resource;
import javax.ejb.ActivationConfigProperty;
import javax.ejb.EJB;
import javax.ejb.MessageDriven;
import javax.ejb.MessageDrivenContext;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageListener;
import javax.jms.ObjectMessage;
 
@MessageDriven(
   name = "BookMessageHandler",
   activationConfig = {
      @ActivationConfigProperty( propertyName = "destinationType", 
                                 propertyValue = "javax.jms.Queue"),
      @ActivationConfigProperty( propertyName = "destination", 
                                 propertyValue ="/queue/BookQueue")
   }
)
public class LibraryMessageBean implements MessageListener {
 
   @Resource
   private MessageDrivenContext mdctx;  
 
   @EJB
   LibraryPersistentBeanRemote libraryBean;
 
   public LibraryMessageBean(){        
   }
 
   public void onMessage(Message message) {
      ObjectMessage objectMessage = null;
      try {
         objectMessage = (ObjectMessage) message;
         Book book = (Book) objectMessage.getObject(); 
         libraryBean.addBook(book);
 
      } catch (JMSException ex) {
         mdctx.setRollbackOnly();
      }       
   }   
}

EJBTester (EJB Client)

EJBTester.java

package com.tutorialspoint.test;
   
import com.tutorialspoint.entity.Book;
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.jms.ObjectMessage;
import javax.jms.Queue;
import javax.jms.QueueConnection;
import javax.jms.QueueConnectionFactory;
import javax.jms.QueueSender;
import javax.jms.QueueSession;
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.testMessageBeanEjb();
   }
   
   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 testMessageBeanEjb(){
 
      try {
         int choice = 1; 
         Queue queue = (Queue) ctx.lookup("/queue/BookQueue");
         QueueConnectionFactory factory =
         (QueueConnectionFactory) ctx.lookup("ConnectionFactory");
         QueueConnection connection =  factory.createQueueConnection();
         QueueSession session = connection.createQueueSession( 
         false, QueueSession.AUTO_ACKNOWLEDGE);
         QueueSender sender = session.createSender(queue);
 
         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);
               ObjectMessage objectMessage = 
               session.createObjectMessage(book);
               sender.send(objectMessage); 
            } else if (choice == 2) {
               break;
            }
         }
 
         LibraryPersistentBeanRemote libraryBean = 
         (LibraryPersistentBeanRemote)
		 ctx.lookup("LibraryPersistentBean/remote");
 
         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做以下任务。

jndi.properties中加载和初始化的InitialContext对象。
JNDI查找testStatefulEjb（）方法，完成了名字 - “/queue/BookQueue”在JBoss获得参考。发件人使用队列会话创建。
然后用户显示一个库存储的用户界面和他/她被要求输入选择。
如果用户输入1，系统要求输入书籍名称和发件人发送本书的名字来排队。当JBoss容器接收到这个消息队列，它会调用我们的消息驱动bean的onMessage方法。消息驱动bean保存使用状态会话bean addBook（）方法的书。会话Bean持久化这本书中通过EntityManager调用数据库。
如果用户输入2，然后是另一个JNDI查找名字 - “LibraryStatefulSessionBean/remote”获取远程业务对象（状态EJB）再次上市的书籍完成。

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 EJB
**********************
Welcome to Book Store
**********************
Options 
1. Add Book
2. Exit 
Enter Choice: 2
Book(s) entered so far: 2
1. learn java
1. learn EJB
BUILD SUCCESSFUL (total time: 15 seconds)

输出上面显示说我们的消息驱动bean接收消息和持久性存储和书籍从数据库中检索存储本书。
我们的消息驱动bean被使用LibraryPersistentBean使用@ EJB注释注入的情况下例外MessageDrivenContext对象用于回滚事务。