在 Java EE 应用程序中实现重新连接逻辑

此过程的示例代码如下：

public class SimpleServlet extends HttpServlet {   
  public void doGet(HttpServletRequest request,                      
                    HttpServletResponse response)     
       throws ServletException, IOException {     
          try {      
 // get connection factory/ queue       
 InitialContext ic = new InitialContext();       
 ConnectionFactory cf =                 
           (ConnectionFactory)ic.lookup("java:comp/env/jms/WMQCF");  
 Queue q = (Queue) ic.lookup("java:comp/env/jms/WMQQueue");       

 // send a message       
 Connection c = cf.createConnection();  
 Session s = c.createSession(false, Session.AUTO_ACKNOWLEDGE);  
 MessageProducer p = s.createProducer(q);    
 Message m = s.createTextMessage();  
 p.send(m); 

 // done, release the connection 
 c.close();
 }
 catch (JMSException je) {  
 // process exception 
   } 
 } 
}

如果调用者无法处理 servlet 中的故障，那么必须在应用程序内处理重新连接。 如以下示例中所示，要处理应用程序中的重新连接，需要应用程序请求新连接，以便它可以对从 JNDI 查找的连接工厂进行高速缓存，并处理 JMSException ，例如 JMSCMQ0001: WebSphere MQ call failed with compcode '2' ('MQCC_FAILED') reason '2009' ('MQRC_CONNECTION_BROKEN').

public void doGet(HttpServletRequest request, HttpServletResponse response) 
      throws ServletException, IOException { 

  // get connection factory/ queue 
  InitialContext ic = new InitialContext(); 
  ConnectionFactory cf = (ConnectionFactory) 
               ic.lookup("java:comp/env/jms/WMQCF"); 
  Destination destination = (Destination) ic.lookup("java:comp/env/jms/WMQQueue"); 

  setupResources(); 
  
  // loop sending messages 
  while (!sendComplete) { 
    try { 
      // create the next message to send 
      msg.setText("message sent at "+new Date()); 
      // and send it 
      producer.send(msg); 
    } 
    catch (JMSException je) { 
        // drive reconnection 
        setupResources(); 
    } 
  } 

在以下示例中， setupResources() 创建 JMS 对象并包含用于处理非瞬时重新连接的休眠和重试循环。 事实上，此方法会阻止许多重新连接尝试。 请注意，为了清晰起见，示例中已省略出口条件。

 private void setupResources() { 

    boolean connected = false; 
    while (!connected) { 
      try { 
        connection = cf.createConnection(); // cf cached from JNDI lookup 
        session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE); 
        msg = session.createTextMessage(); 
        producer = session.createProducer(destination); // destination cached from JNDI lookup 
        // no exception? then we connected ok 
        connected = true; 
      } 
      catch (JMSException je) { 
        // sleep and then have another attempt 
        try {Thread.sleep(30*1000);} catch (InterruptedException ie) {} 
      } 
    } 

对于处理时间超过几十秒的长寿命应用程序 (例如，批处理) ，可以使用 WebSphere® Application Server WorkManager 。 WebSphere Application Server 的代码片段示例如下所示:

public class BatchSenderServlet extends HttpServlet  { 
  
  private WorkManager workManager = null; 
  private MessageSender sender; // background sender WorkImpl 
  
  public void init() throws ServletException { 
    InitialContext ctx = new InitialContext(); 
    workManager = (WorkManager)ctx.lookup(java:comp/env/wm/default); 
    sender = new MessageSender(5000); 
    workManager.startWork(sender); 
  } 

  public void destroy() { 
    sender.halt(); 
  } 

  public void doGet(HttpServletRequest req, HttpServletResponse res) 
                               throws ServletException, IOException { 
    res.setContentType("text/plain"); 
    PrintWriter out = res.getWriter(); 
    if (sender.isRunning()) { 
      out.println(sender.getStatus()); 
    } 
} 

其中 web.xml 包含：

<resource-ref> 
      <description>WorkManager</description> 
      <res-ref-name>wm/default</res-ref-name> 
      <res-type>com.ibm.websphere.asynchbeans.WorkManager</res-type> 
      <res-auth>Container</res-auth> 
      <res-sharing-scope>Shareable</res-sharing-scope> 
   </resource-ref> 

而且，现在已通过 Work 接口实现了批处理：

import com.ibm.websphere.asynchbeans.Work; 

public class MessageSender implements Work { 

  public MessageSender(int messages) {numberOfMessages = messages;} 

  public void run() { 
    // get connection factory/ queue 
    InitialContext ic = new InitialContext(); 
    ConnectionFactory cf = (ConnectionFactory) 
               ic.lookup("java:comp/env/jms/WMQCF"); 
    Destination destination = (Destination) ic.lookup("jms/WMQQueue"); 

    setupResources(); 
  
    // loop sending messages 
    while (!sendComplete) { 
      try { 
        // create the next message to send 
        msg.setText("message sent at "+new Date()); 
        // and send it 
        producer.send(msg); 
        // are we finished? 
        if (sendCount == numberOfMessages) {sendComplete = true); 
      } 
      catch (JMSException je) { 
          // drive reconnection 
          setupResources(); 
      } 
  } 

  public boolean isRunning() {return !sendComplete;} 

  public void release() {sendComplete = true;}