我想在我的网站上实时显示所有在线用户。虽然不知道如何去做。在新用户登录后添加新用户并不难，但是我还需要删除不再登录的用户。

任何想法如何做到这一点？我应该使用jQuery检查哪些用户已注销并从列表中将其删除吗？

最佳答案

您的问题将是人们在不注销的情况下离开，他们的 session 将仍然存在多长时间，直到您设置了超时时间才可以收集他们的 session 数据(实际上可能更长)

为了获得真正准确的登录者和访问站点的计数，您将需要每个客户端每隔几秒钟或几分钟向服务器发送一次“心跳”。在每个心跳触发器上，您都希望使在指定时间内未 checkin 的所有用户过期。

心跳信号可能最好至少由用户名和时间戳组成，但可以包含您要跟踪的任何信息。

当客户端向服务器发送单曲时，它会检查该用户名的现有记录，如果记录已经存在，则覆盖时间戳信息，否则添加新记录。后记会删除所有尚未 checkin 的用户条目。最好使信号比到期更频繁地发生。每30秒发出一次信号，每分钟清理一次。

(编辑后，改变了主意，最好按相同的顺序而不是分别地进行所有操作)
然后从 Activity 表返回当前登录的用户，这就像SELECT * FROM table一样容易，因为该表始终是干净的。

客户端:

这是客户端库的一个简单示例，用于处理触发心跳功能并捕获结果。

//Client-side parent variable declaration (simulated namespacing)
var Client = Client || {};
Client.Pulse = null; //Holds a pointer to the heartbeat timer (id)
/* If you needed to cancel the heartbeat processes you could
 * pass this variable to clearTimeout(). Calling Client.Heartbeat()
 * again would start the cycle back up.
 */

//Initial event that will kick off the chain when the DOM is ready
$(document).ready(function(){
  Client.Heartbeat(); //Initial call to the Heartbeat function
});//ready

/// Sends the heartbeat signal and retrieves the currently active user list
Client.Heartbeat = function(){
  var sUsername = 'SomeUser';
  /* Note: If you have an active session running on the server it would not be 
   * necessary to send the username since you could pull it on the backend 
   * script which would be more tamper-proof anyway. I'm just giving an
   * example of sending data to the server using the jQuery.ajax method
   * If you were storing the username to be sent from the client; this wouldn't 
   * be a good place to do it anyway
   * 
   * Remove the "data : {...}" line below to exclude sending information to the server
   * The "type : 'post'" line would not be necessary either 
   */

  $.ajax({ //Send the signal and recieve the information about active users back
    url : '/lib/server/Heartbeat.php',
    type : 'post',
    dataType : 'json',
    data : {Username : sUsername },
    success : function(jActiveUsers,sStatus,jqXHR){ 
      /* This is the callback function of the request, jActiveUsers will be the 
       * json object with the information you choose to send back to it
       */
      Client.RenderActiveUsers(jActiveUsers); //Call the display function
      //Trigger the next delayed call to Client.Heartbeat
      Client.Pulse = setTimeout(function(){
        Client.Heartbeat();
      },30000); //30 second delay before next trigger
    }//success
  });//$.ajax
}//Heartbeat

/// Processes the results sent by the server and draws them to the UI
Client.RenderActiveUsers = function(jActiveUsers){
  /* This is where you would get a handle whatever element(s) on the page
   * will be displaying the information about currently active users
   * and filling it with the list of users how ever you would wish to display it.
   */
}//RenderActiveUsers

I apologize I am not familiar with Java as a back-end service, I will be making some assumptions based on how PHP works; so I cannot guarantee it will map directly to your environment. Database examples will assume MySQL. code examples will be pseudo-cody PHP(ish)

 ActiveUsers
 -----------------------------------------
 |   Field    |    Type     | NULL | Key |
 -----------------------------------------
 | Id         | int         |      | PRI |
 | Username   | varchar(xx) |      |     |
 | LastPulse  | datetime    |      |     |
 | FirstPulse | datetime    |      |     |
 -----------------------------------------

if($LoggedIn && ($Username != null)){ //Session information

SELECT `Id` FROM `ActiveUsers` WHERE `Username` = '{$Username}' LIMIT 1

UPDATE `ActiveUsers` SET `LastPulse` = NOW() WHERE `Id` = {$Id}

INSERT INTO `ActiveUsers` (`Username`,`LastPulse`,`FirstPulse`) VALUES ('{$Username}',NOW(),NOW()) 

DELETE FROM `ActiveUsers` WHERE `LastPulse` < (NOW() - INTERVAL 2 MINUTE)

SELECT `Username`, UNIX_TIMESTAMP(`FirstPulse`) AS `FirstPulse` FROM `ActiveUsers` ORDER BY `FirstPulse` ASC

关于java - 如何使用Ajax显示在线用户，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/7867517/