EJB依賴注入

EJB 3.0規範提供了註釋字段或setter方法注入依賴可以應用。 EJB容器使用的全局JNDI註冊表定位的依賴。以下註解在EJB 3.0中使用依賴注入。

@EJB - 用來注入其他EJB引用。
@Resource - 用於注入數據源或單例服務，如sessionContext，timerService等

@EJB使用步驟

@EJB 可以使用欄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 使用步驟

@Resource 通常用於注入EJB容器提供單例。

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

示例應用程序

讓我們創建一個測試EJB應用程序來測試EJB服務的依賴注入。

Step

Description

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

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

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

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.

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

Add Book
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做以下任務。

jndi.properties中加載和初始化的InitialContext對象。
JNDI查找testStatefulEjb（）方法，完成了名字 - 「/queue/BookQueue」在JBoss獲得參考。發件人使用隊列會話創建。
然後用戶顯示一個庫存儲的用戶界面和他/她被要求輸入選擇。
如果用戶輸入1，系統要求輸入書籍名稱和發件人發送本書的名字來排隊。當JBoss容器接收到這個消息隊列，它會調用我們的消息驅動bean的onMessage方法。消息驅動bean保存使用狀態會話bean addBook（）方法的書。會話Bean持久化這本書中通過EntityManager調用數據庫。
如果用戶輸入2，然後是另一個JNDI查找名字 - 「LibraryStatefulSessionBean/remote」獲取遠程業務對象（狀態EJB）再次上市的書籍完成。

運行客戶端訪問EJB

在項目資源管理器中找到EJBTester.java。右鍵點擊上EJBTester類，並選擇run file.

在Netbeans控制檯驗證以下輸出。

run:
**********************
Welcome to Book Store
**********************
Options

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

輸出上面顯示說我們的消息驅動bean接收消息和持久性存儲和書籍從數據庫中檢索存儲本書。
我們的消息驅動bean被使用LibraryPersistentBean使用@ EJB註釋注入的情況下例外MessageDrivenContext對象用於回滾事務。