📅 最后修改于: 2020-11-16 06:16:35 🧑 作者: Mango
消息驱动Bean是一种企业Bean，当EJB容器从队列或主题接收到消息时，它将被EJB容器调用。消息驱动Bean是无状态Bean，用于异步执行任务。
为了演示消息驱动bean的使用，我们将使用EJB-persistence一章，我们需要执行以下任务-
步骤1-在数据库中创建表(请参阅EJB-Persistence一章)。
步骤2-创建与表相对应的Entity类(请参阅EJB-Persistence一章)。
步骤3-创建数据源和持久性单元(请参阅EJB持久性一章)。
步骤4-创建具有EntityManager实例的无状态EJB(请参阅EJB-Persistence一章)。
步骤5-更新无状态ejb.Add方法以添加记录并通过实体管理器从数据库获取记录(请参阅EJB-Persistence一章)。
步骤6-在JBoss默认应用程序目录中创建一个名为BookQueue的队列。
步骤7-基于控制台的应用程序客户端将消息发送到此队列。
步骤8-创建一个消息驱动Bean，它将使用无状态Bean来保存客户端数据。
步骤9 -EJB容器的jboss将调用上述消息驱动的bean，并将客户端将发送到的消息传递给它。
如果
在这里，我们创建一个名为BookQueue的队列-
jbossmq-destinations-service.xml
jboss.mq:service=DestinationManager
当启动JBoss时，您会在jboss日志中看到类似的条目。
...
10:37:06,167 INFO [QueueService] Queue[/queue/BookQueue] started, fullSize=200000, pageSize=2000, downCacheSize=2000
...
@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) {
}
}
LibraryMessageBean带有@MessageDriven注释，以将其标记为消息驱动的Bean。
其属性定义为destinationType-队列和destination-/ queue / BookQueue。
它实现了MessageListener接口，该接口公开了onMessage方法。
它具有MessgeDrivenContext作为资源。
为了持久性目的，将LibraryPersistentBeanRemote无状态bean注入到该bean中。
生成EjbComponent项目并将其部署在JBoss上。构建和部署EJB模块之后，我们需要一个客户端将消息发送到jboss队列。
让我们创建一个测试EJB应用程序来测试消息驱动Bean。
| Step | Description |
|---|---|
| 1 |
Create a project with a name EjbComponent under a package com.tutorialspoint.entity as explained in the EJB – Create Application chapter. You can also use the project created in EJB – Create Application chapter as such for this chapter to understand EJB persistence concepts. |
| 2 |
Create Book.java under package com.tutorialspoint.entity as created in EJB-Persistence chapter. |
| 3 |
Create LibraryPersistentBean.java and LibraryPersistentBeanRemote as created in EJB-Persistence chapter. |
| 4 |
Create jboss-ds.xml in EjbComponent > setup folder and persistence.xml in EjbComponent > src > conf folder. These folders can be seen in files tab in Netbeans as created in EJB-Persistence chapter. |
| 5 |
Create LibraryMessageBean.java under a package com.tutorialspoint.messagebean and modify it as shown below. |
| 6 |
Create BookQueue queue in Jboss as described above. |
| 7 |
Clean and Build the application to make sure business logic is working as per the requirements. |
| 8 |
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. |
| 9 |
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. Modify it as shown below. |
package com.tutorialspoint.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();
}
}
}
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，发送方将书名发送到队列。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。
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。