如何查找会话变量是否存在

Question

我如何找到值在会话中是否设置为变量？

if(session.getAttribute("tot_demand"))//need to change

  //if value is already set then do this.

else

  //if not set then do this.

我需要写什么,以使上述代码有效？

Answer 1

比较null:

if (session.getAttribute("tot_demand") != null) {
   // already set
} else {
   // not yet set
}