Struts2 Medium OGNL The expression language is right Xwork Of OGNL Encapsulation . We need to understand a few points : 
1. Struts2 Lieutenant general ActionContext As OGNL Context of (ActionContext There's one inside Map object ) 
2. Struts2 Medium OGNL The root object of an expression language is a ValueStack,ValueStack Every object in is treated as a root object . 
Struts2 The framework will instantiate Action Objects in the ValueStack in , If it is Action chain , Multiple Action All exist in ValueStack in . and ValueStack In addition to Action Outside ,Struts2 The framework will also parameters,request,response,session,application,attr Wait for the object to be placed in ActionContext in , Access to these objects needs to be prefixed #.

summary :Struts2 The data processing in is based on Xwork Of OGNL, It's in OGNL On the basis of a certain package .OGNL The core concept of is the root object (root) And context (context)--- You can pass in a Map Object as context , To them put Enter an object , So this object can be used as the root object (ognl You can pass in different Map Object as the root object , You can also specify different root objects , and Struts2 in , It fixes the root object ValueStack). stay Struts2 in ,ActionContext As OGNL Context of , Its root object is a ValueStack,ValueStack Each object in is treated as a root object .Struts2 Medium Action Exists as a root object ( If more than one Action With chain There is a form of , Multiple Action All exist in ValueStack in , Are root objects ).

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