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📜  EJB-依赖注入

📅  最后修改于: 2020-11-16 06:20:35             🧑  作者: Mango

EJB 3.0规范提供了注释，可以将其应用于字段或setter方法以注入依赖项。 EJB容器使用全局JNDI注册中心来定位依赖关系。以下注释在EJB 3.0中用于依赖项注入。

  • @EJB-用于注入其他EJB参考。

  • @Resource-用于注入数据源或单例服务，例如sessionContext，timerService等。

使用@EJB的步骤

@EJB可以按以下方式在字段或方法上使用-

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;
   }
   ...
}

使用@Resource的步骤

@Resource通常用于注入EJB容器提供的单例。

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

应用范例

让我们创建一个测试EJB应用程序，以测试EJB中的依赖注入服务。

Step Description
1

Create a project with a name EjbComponent under a package com.tutorialspoint.timer as explained in the EJB – Create Application chapter.
2

Use Beans created in the EJB – Message Driven Bean chapter. Keep rest of the files unchanged.
3

Clean and Build the application to make sure business logic is working as per the requirements.
4

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.
5

Now create the EJB client, a console based application in the same way as explained in the EJB – Create Application chapter under topic Create Client to access EJB.

EJBComponent(EJB模块)

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客户端)

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 \n1. Add Book\n2. Exit \nEnter 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 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执行以下任务-

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

  • 在testStatefulEjb()方法中，使用名称“ / queue / BookQueue”完成jndi查找，以获得Jboss中可用队列的引用。然后使用队列会话创建发件人。

  • 然后，向用户显示一个库存储用户界面，并要求他/她输入选择。

  • 如果用户输入1，则系统要求输入书名，发送者将书名发送到队列。当JBoss容器在队列中接收到此消息时，它将调用消息驱动bean的onMessage方法。然后，我们的消息驱动bean使用有状态会话bean addBook()方法保存书籍。会话Bean通过EntityManager调用将书籍保留在数据库中。

  • 如果用户输入2，则将使用名称“ LibraryStatefulSessionBean / remote”进行另一个jndi查找，以再次获取远程业务对象(有状态EJB)，并完成了书的清单。

运行客户端以访问EJB

在项目资源管理器中找到EJBTester.java。右键单击EJBTester类，然后选择运行文件。

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 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)

上面显示的输出表明，我们的消息驱动bean正在接收消息并将书存储在持久性存储中，并且从数据库中检索了书。

我们的消息驱动bean使用通过@EJB注释注入到其中的LibraryPersistentBean，如果发生异常，则将MessageDrivenContext对象用作回滚事务。