How to encapsulate request parameters in struts 2

As we all know, the action class of struts 2 can obtain all relevant values through attributes, such as request parameters, action configuration parameters Pass attribute values (through chain results) to other actions, etc. the only thing we need to do to obtain these parameter values is to declare an attribute with the same name as the parameter in the action class. The corresponding action attribute will be assigned before struts 2 calls the action method of the action class (the default is the execute method).

To accomplish this function, struts 2 depends largely on the ValueStack object. This object runs through the whole life cycle of action (each object instance of action class will have a ValueStack object). When struts 2 receives a. Action request, it will first create an object instance of action class, but will not call the action method, but first put the corresponding properties of action class into the top-level node of ValueStack object (ValueStack object is equivalent to a stack). Only all property values are default values, such as null for string type, 0 for int type, etc.

After handling the above work, struts 2 will call the interceptors in the interceptor chain. After calling all interceptors, it will finally call the action method of the action class. Before calling the action method, it will assign the attribute value in the top-level node of the ValueStack object to the corresponding attribute in the action class. You should note that this has brought us great flexibility. In other words, during the process of calling the interceptor by struts 2, you can change the value of the attribute in the ValueStack object. When a certain attribute value is changed, the corresponding attribute value of the action class will change to the value of the attribute last changed in the interceptor.

From the above description, it is easy to know that the action class in struts 2 can obtain parameter values with the same name as the attribute through different interceptors. For example, the interceptor for obtaining request parameters is params, and the interceptor for obtaining action configuration parameters is staticparams. Read the corresponding values inside these interceptors and update the values of the corresponding attributes of the top-level node of the ValueStack object. The ValueStack object is like a conveyor belt, which transfers the attribute value from one interceptor to another interceptor (of course, the attribute value may change during this period), and finally to the action object, and assigns the final value of the attribute in the ValueStack object to the corresponding attribute of the action class.

When we use El expressions in the display layer, we can access not only the attributes of 11 hidden objects in El expressions, but also the object attribute values in ValueStack, because struts 2 further encapsulates HttpServletRequest

summary

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