防止一个用户登录多次的方法(转帖)
在web开发时,有的系统要求同一个用户在同一时间只能登录一次,也就是如果一个用户已经登录了,在退出之前如果再次登录的话需要报错。
常见的处理方法是,在用户登录时,判断此用户是否已经在Application中存在,如果存在就报错,不存在的话就加到Application中(Application是所有Session共有的,整个web应用程序唯一的一个对象):
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当然这里使用Cache等保存也可以。
接下来就是要在用户退出的时候将此用户从Application中去除,我们可以在Global.asax的Session_End事件中处理:
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这些都没有问题,有问题的就是当用户直接点浏览器右上角的关闭按钮时就有问题了。因为直接关闭的话,并不会立即触发Session过期事件,也就是关闭浏览器后再来登录就登不进去了。
这里有两种处理方式:
1、使用Javascript方式
在每一个页面中加入一段javascript代码:
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由于onbeforeunload方法在浏览器关闭、刷新、页面调转等情况下都会被执行,所以需要判断是点击了关闭按钮或是按下Alt+F4时才执行真正的关闭操作。
然后在logout.aspx的Page_Load中写和Session_End相同的方法,同时在logout.aspx中加入事件:onload="javascript:window.close()"
但是这样还是有问题,javascript在不同的浏览器中可能有不同的行为,还有就是当通过文件->关闭时没有判断到。
2、使用xmlhttp方法(这种方法测试下来没有问题)
在每个页面中加入如下的javascript(这些javascript也可以写在共通里,每个页面引入就可以了)
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在web.config中设置
<sessionState mode="InProc" timeout="1"></sessionState>
test.aspx页面就是一个空页面,只不过需要在Page_Load中加入:
Response.Expires = -1;
保证不使用缓存,每次都能调用到这个页面。
原理就是:设置Session的过期时间是一分钟,然后在每个页面上定时每30秒连接一次测试页面,保持Session有效,总共连60次,也就是30分钟。如果30分钟后用户还没有操作,Session就会过期。当然,如果用户直接关闭浏览器,那么一分钟后Session也会过期。这样就可以满足要求了。
来自:http://www.cnblogs.com/firstyi/archive/2007/08/08/847301.html
跟我想的差不多,稍微改下就可以做在线人数了呵呵。