如何使用JSTL标记检查Spring mvc 3中的Session变量是否包含null或Not(How to check if a Session variable contain null or N

如何使用JSTL标记检查Spring mvc 3中的Session变量是否包含null或Not(How to check if a Session variable contain null or Not in spring mvc 3 using JSTL tag )

想要检查会话变量“Sess_Var”是否包含null

<c:if test="${Sess_Var=='NULL'}" > <% response.sendRedirect("doLogin.obj"); %>

但它不起作用，它没有检查它

Want to check that session Variable "Sess_Var" contain null or not

<c:if test="${Sess_Var=='NULL'}" > <% response.sendRedirect("doLogin.obj"); %>

But its not working,It doesnt check it

最满意答案

如果你的意思是要检查它是否为NULL（而不是检查变量是否包含字符串'NULL'，那么你可以这样做

<c:if test="${empty Sess_Var}">

这将检查变量是空还是null，如果是，则计算结果为true 。

If you mean you want to check if it is NULL (as opposed to checking if the variable contain the String 'NULL' then you could do

<c:if test="${empty Sess_Var}">

This checks to see whether the variable is empty or null and evaluates to true if it is either.