Question

servlet session

最近项目上出现了一个错误
大致代码就是
用servlet include了几个jsp文件，然后session就消失了
但在include之前有session
则 request.getSession()就出错了
Cannot create a session after the response has been committe
但是这个问题不是每次都出现，只是偶尔出现，在开发环境中也没出现过，在tomcat 中会偶尔出现几次
虽然说只要把request.getSession()改成request.getSession(false)问题就解决了
但是我想知道为什么include之后session就消失了。
看了一会源代码没有找到地方，我用的tomcat 5.5 请比较熟悉原代码的人解释一下

Answer 1

看看文档吧
getSession
public HttpSession getSession(boolean create)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