Question

请教servlet中getsession的用法

HttpSession session = request.getSession(false);
HttpSession session = request.getSession(true);
HttpSession session = request.getSession();
这三种分别什么意思

Answer 1

getSession是返回当前用户的会话对象，参数的区别在于

参数为true，则如果“当前用户的会话对象”为空（第一次访问时）则创建一个新的会话对象返回

参数为false，则如果“当前用户的会话对象”为空，则返回null（即不自动创建会话对象）

注意request.getSession() 等同于 request.getSession(true)，除非我们确认session一定存在或者sesson不存在时明确有创建session的需要，否则请尽量使用request.getSession(false)。

Answer 2

Returns the current HttpSession associated with this request or, if if there is no current session and create is true, returns a new session.
If create is false and the request has no valid HttpSession, this method returns null.

To make sure the session is properly maintained, you must call this method before the response is committed. If the container is using cookies to maintain session integrity and is asked to create a new session when the response is committed, an IllegalStateException is thrown.

Parameters:
true - to create a new session for this request if necessary; false to return null if there's no current session
Returns:
the HttpSession associated with this request or null if create is false and the request has no valid session
See Also:
getSession()

Answer 3

去看看文档好了！那是官方的。应该是最准确的