TimerService 與 Timer 回呼


以下使用一個簡單的範例，示範如何在Stateless Session Bean上使用Timer服務，客戶端可以指定時間啟動Timer，排定在某個時間送訊息給Message-Driven Bean。

首先定義一個簡單的介面：
  • IMaintain.java
package onlyfun.caterpillar;

import java.util.Date;
import javax.ejb.Local;

@Local
public interface IMaintain {
    public void scheduleMessage(Date expiration, String message);
}

在Stateless Session Bean實作部份，使用@Resource注入TimerService、ConnectionFactory與Destination：
  • MaintainBean.java
package onlyfun.caterpillar;

import java.util.Date;
import javax.annotation.Resource;
import java.util.logging.*;
import javax.ejb.*;
import javax.jms.*;

@Stateless
public class MaintainBean implements IMaintain {
    @Resource(name="jms/HelloQueueFactory")
    private ConnectionFactory connectionFactory;
    
    @Resource(name="jms/HelloQueue")
    private Destination queue;
    
    @Resource 
    private TimerService timerService;

    public void scheduleMessage(Date expiration, String message) {
        timerService.createTimer(expiration, message);
    }

    @Timeout
    public void sendMessage(Timer timer) {
        try {
            String message = (String) timer.getInfo();

            Connection connection = connectionFactory.createConnection();
            Session session = connection.createSession(
                    false, Session.AUTO_ACKNOWLEDGE);
            MessageProducer producer = session.createProducer(queue);
            TextMessage textMessage = session.createTextMessage();
            textMessage.setText(message);
            producer.send(textMessage);

            producer.close();
            session.close();
            connection.close();
        } catch (JMSException ex) {
            Logger.getLogger(
                    MaintainBean.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}

如果您想要從EJBContext中取得TimerService，則可以如下：
...
@Resource
private SessionContext context;

public void scheduleMessage(Date expiration, String message) {
    TimerService timerService = context.getTimerService();
    timerService.createTimer(expiration, message);
}
....

若不使用@Timeout標註，則您要實作TimedObject介面，實作其void ejbTimeout(Timer timer)方法。

為了配合這個範例，改寫一下 第 一個 Message-Driven Bean 中的Message-Driven Bean範例：
  • HelloMessageBean.java
package onlyfun.caterpillar;

import java.util.logging.Level;
import java.util.logging.Logger;
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(mappedName = "jms/HelloQueue",
   activationConfig =  {
        @ActivationConfigProperty(propertyName = "acknowledgeMode",
                                  propertyValue = "Auto-acknowledge"),
        @ActivationConfigProperty(propertyName = "destinationType", 
                                  propertyValue = "javax.jms.Queue")
    })
public class HelloMessageBean implements MessageListener {
    
    public void onMessage(Message message) {
        try {
            TextMessage txtMessage = (TextMessage) message;
            System.out.println(txtMessage.getText() + " processed....Orz");
        } catch (JMSException ex) {
            Logger.getLogger(HelloMessageBean.class.getName())
                    .log(Level.SEVERE, null, ex);
        }
    }
}

以下是個簡單的Servlet客戶端測試，排定在呼叫後的10秒鐘執行：
  • HelloServlet.java
package onlyfun.caterpillar;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;
import javax.ejb.EJB;

public class HelloServlet extends HttpServlet {
    @EJB
    private IMaintain maintain;
   
    protected void processRequest(HttpServletRequest request, 
                                HttpServletResponse response)
                        throws ServletException, IOException {
        Calendar calendar = Calendar.getInstance();
        calendar.add(Calendar.MILLISECOND, 10000);
        maintain.scheduleMessage(calendar.getTime(), "save me....XD");
    } 

    protected void doGet(HttpServletRequest request, 
                         HttpServletResponse response)
                       throws ServletException, IOException {
        processRequest(request, response);
    } 

    protected void doPost(HttpServletRequest request,
                          HttpServletResponse response)
                       throws ServletException, IOException {
        processRequest(request, response);
    }

    public String getServletInfo() {
        return "Short description";
    }
}