java – EJB服务器端是否可以向EJB客户端发送事件?

我想知道是否有可能沿着这些方向做点什么:

1)服务器端(EJB类)

@Statefull
public class SomeEJB implements SomeEJBRemote {

@Resource
private SessionContext sessionContext;

//(...)
public void someMethod(Record record){
    //(...)
    //Situation that requires the server to alert all registered listeners
    if(specialSituation){
        sessionContext.fireEventToListeners(new SomeEvent());
    }

    //Do something else...
}
}

2)客户端

//(...) 
SomeEJBRemote ejb = initialContext.lookup("SomeEJBRemote");
ejb.addListener(this);

void EJBEventListener(SomeEvent event){
    System.out.println("EJB server has sent an event!");
}

A)Java EE规范中是否有允许这样做的内容?

B)我知道JBoss允许某种双向通信,但我可以这样做吗?

C)OpenEJB(或TOMEE)中有这样的东西吗?

最佳答案
在客户端中使用嵌入式EJB容器和MDB很容易.我们有一个例子就是这样做的.

查看this example的监视器模块.

在10,000英尺处,此示例执行以下操作:

服务器端:

> @Stateless bean包装对EntityManager的访问
> JMS消息发送到所有添加/删除操作的主题

客户端:

>嵌入式EJB容器/ MDB接收消息
>收到后,将通过java.awt.SystemTray向用户发出通知

所以关于这种技术的有趣之处在于它是完全事务性的 – EntityManager更新和发送的JMS消息都是事务的一部分.如果数据库更新失败,则不会发送任何JMS消息.

这是该示例中100%的客户端代码.做什么并不需要做太多的描述.

客户端“主”类

import javax.naming.InitialContext;
import javax.naming.NamingException;
import java.awt.AWTException;
import java.awt.Image;
import java.awt.MenuItem;
import java.awt.PopupMenu;
import java.awt.SystemTray;
import java.awt.Toolkit;
import java.awt.TrayIcon;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.net.MalformedURLException;
import java.net.URL;

public class NotificationMonitor {
    private static TrayIcon trayIcon;

    public static void main(String[] args) throws NamingException, InterruptedException, AWTException, MalformedURLException {
        addSystemTrayIcon();

        // Boot the embedded EJB Container 
        new InitialContext();

        System.out.println("Starting monitor...");
    }

    private static void addSystemTrayIcon() throws AWTException, MalformedURLException {
        SystemTray tray = SystemTray.getSystemTray();

        URL moviepng = NotificationMonitor.class.getClassLoader().getResource("movie.png");
        Image image = Toolkit.getDefaultToolkit().getImage(moviepng);

        ActionListener exitListener = new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                System.out.println("Exiting monitor...");
                System.exit(0);
            }
        };

        PopupMenu popup = new PopupMenu();
        MenuItem defaultItem = new MenuItem("Exit");
        defaultItem.addActionListener(exitListener);
        popup.add(defaultItem);

        trayIcon = new TrayIcon(image, "Notification Monitor", popup);
        trayIcon.setImageAutoSize(true);
        tray.add(trayIcon);
    }

    public static void showAlert(String message) {
        synchronized (trayIcon) {
            trayIcon.displayMessage("Alert received", message, TrayIcon.MessageType.WARNING);
        }
    }
}

客户端MDB

import javax.ejb.ActivationConfigProperty;
import javax.ejb.MessageDriven;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageListener;
import javax.jms.TextMessage;

@MessageDriven(activationConfig = {
        @ActivationConfigProperty(propertyName = "destinationType", propertyValue = "javax.jms.Topic"),
        @ActivationConfigProperty(propertyName = "destination", propertyValue = "notifications")})
public class NotificationsBean implements MessageListener {

    public void onMessage(Message message) {
        try {
            TextMessage textMessage = (TextMessage) message;
            String text = textMessage.getText();

            NotificationMonitor.showAlert(text);
        } catch (JMSException e) {
            e.printStackTrace();
        }
    }
}

客户端jndi.properties文件

这会配置嵌入式EJB容器.您也可以在代码中执行此操作.

java.naming.factory.initial=org.apache.openejb.client.LocalInitialContextFactory
Default\ JMS\ Resource\ Adapter=new://Resource?type=ActiveMQResourceAdapter
Default\ JMS\ Resource\ Adapter.BrokerXmlConfig=broker:vm://localhost
Default\ JMS\ Resource\ Adapter.ServerUrl=tcp://localhost:61616

转载注明原文:java – EJB服务器端是否可以向EJB客户端发送事件? - 代码日志