4个访问范围
requestScope ---->request
sessionScope ---->session
applicationScope ---->application
pageScope --->pageScope
注意:在用el表达式不适用范围的时候,默认查找顺序
先查pageScope --->requestScope ---->sessionScope ---->applicationScope
requestScope ---->request
sessionScope ---->session
applicationScope ---->application
pageScope --->pageScope
注意:在用el表达式不适用范围的时候,默认查找顺序
先查pageScope --->requestScope ---->sessionScope ---->applicationScope