ScheduledExecutorService類做的定時更新代碼

 import java.util.Date;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import javax.servlet.ServletContext;

public class OnLineUserDoTimer {

    private  ScheduledExecutorService scheduler = Executors  
            .newScheduledThreadPool(1);   
 
    public void executeTimer( final ServletContext application) {  

        Runnable task = new Runnable() {  
         
            public void run() {  
             removeUser(application); //調用操作實現方法  
            }  
        };  
        if (scheduler.isShutdown()) {  
            scheduler = Executors.newScheduledThreadPool(1);  
            scheduler.scheduleAtFixedRate(task, 0, 60, TimeUnit.SECONDS);  
        } else {  
            scheduler.scheduleAtFixedRate(task, 0, 60, TimeUnit.SECONDS); // 延遲0，每隔60行一次  
        }  
    }  
 
 //停止任務，不再提交新任務，已提交任務會繼續執行以致完成  
  public void stop() {  
        scheduler.shutdown();  
  }
  //刪除時間間隔超過指定值的用戶記錄
  public void removeUser(ServletContext application){
   Object o=application.getAttribute("OnLineUserList");
   if(o!=null){
    Map onLineUserList=(HashMap)o;
    Set keys=onLineUserList.keySet();
    Iterator lt=keys.iterator();
    while(lt.hasNext()){
     Object key=lt.next();
     OnLineUser user=(OnLineUser)onLineUserList.get(key);
     Date lasttime=user.getLastreqTime();
     Date now=new Date();
     int fz=(int)((now.getTime()-lasttime.getTime())/(1000*60));
     if(fz>1){
      onLineUserList.remove(key);
     }
    }
   }
  
  }

}