java中的true、false、null有何不同-创新互联

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java 中 request.getSession(true/false/null)的区别

一、需求原因

现实中我们经常会遇到以下3中用法：

HttpSession session = request.getSession();

HttpSession session = request.getSession(true);

HttpSession session = request.getSession(false);

二、区别

1.      Servlet官方文档说：

public HttpSessiongetSession(boolean create)
Returns the currentHttpSession associated with this request or, if if there is no current sessionand create is true, returns a new session.
If create is falseand the request has no valid HttpSession, this method returns null.
To make sure thesession is properly maintained, you must call this method before the responseis committed. If the Container is using cookies to maintain session integrityand is asked to create a new session when the response is committed, anIllegalStateException is thrown.
Parameters: true -to create a new session for this request if necessary; false to return null ifthere's no current session
Returns: theHttpSession associated with this request or null if create is false and therequest has no valid session

2.      翻译过来的意思是：

getSession(boolean create)意思是返回当前reqeust中的HttpSession ，如果当前reqeust中的HttpSession 为null，当create为true，就创建一个新的Session，否则返回null；

简而言之：

HttpServletRequest.getSession(ture)等同于 HttpServletRequest.getSession() 
HttpServletRequest.getSession(false)等同于 如果当前Session没有就为null；