Java 如何检查会话是否存在？
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How to check if session exists or not?
提问by sarah
I am creating the session using
我正在使用创建会话
HttpSession session = request.getSession();
Before creating session I want to check if it exists or not. How would I do this?
在创建会话之前，我想检查它是否存在。我该怎么做？
回答by aioobe
There is a function request.getSession(boolean create)
有一个功能 request.getSession(boolean create)
Parameters:
create- true to create a new session for this request if necessary; false to return null if there's no current session
参数：
create- 必要时为该请求创建一个新会话；如果没有当前会话，则返回 null
Thus, you can simply pass falseto tell the getSessionto return null if the session does not exist.
因此，如果会话不存在，您可以简单地通过false告诉getSession返回 null。
回答by rakke
HttpSession session = request.getSession(true); if (session.isNew()) { ...do something } else { ...do something else }
HttpSession session = request.getSession(true); if (session.isNew()) { ...做某事} else { ...做其他事}
the .getSession(true)tells java to create a new session if none exists.
.getSession(true)如果不存在，则告诉 java 创建一个新会话。
you might of course also do:
你当然也可以这样做：
if(request.getSession(false) != null){
HttpSession session = request.getSession();
}
have a look at: http://java.sun.com/javaee/6/docs/api/javax/servlet/http/HttpServletRequest.html
看看：http: //java.sun.com/javaee/6/docs/api/javax/servlet/http/HttpServletRequest.html
cheers, J?rgen
干杯，J?rgen
回答by BalusC
If you want to check this beforecreating, then do so:
如果您想在创建之前检查这一点，请执行以下操作：
HttpSession session = request.getSession(false);
if (session == null) {
// Not created yet. Now do so yourself.
session = request.getSession();
} else {
// Already created.
}
If you don't care about checking this aftercreating, then you can also do so:
如果你不在乎创建后检查这个，那么你也可以这样做：
HttpSession session = request.getSession();
if (session.isNew()) {
// Freshly created.
} else {
// Already created.
}
That saves a line and a boolean. The request.getSession()does the same as request.getSession(true).
这样可以节省一行和一个boolean. 在request.getSession()不一样的request.getSession(true)。
回答by Ahmed Hassan Hegazy
if(null == session.getAttribute("name")){
// User is not logged in.
}else{
// User IS logged in.
}
回答by Olav Gr?n?s Gjerde
I would like to add that if you create a new session for every new user connecting to your website then your performance will take a hard hit. Use request.getSession(false) to check if a user has a session. With this method you don't create a new session if you're going to render a view based on if a user is authenticated or not.
我想补充一点，如果您为每个连接到您网站的新用户创建一个新会话，那么您的性能将受到严重打击。使用 request.getSession(false) 检查用户是否有会话。如果您要根据用户是否通过身份验证来呈现视图，则使用此方法无需创建新会话。
