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。
StepDescription
1Create a project with a name EjbComponent under a package com.tutorialspoint.timer as explained in the EJB - Create Application chapter.
3Use Beans created in the EJB - Message Driven Bean chapter. Keep rest of the files unchanged.
5Clean and Build the application to make sure business logic is working as per the requirements.
6Finally, 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.
7Now 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 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。(编辑：雷林鹏 来源：网络|侵删)