struts-default.xml中定义了一系列的拦截器和拦截器链
同时也定义了一个默认的拦截器defaultStack，一旦定义了默认的拦截器，
该拦截器就会对包中的所有的Action起作用，当然如果你的Action中显式地定义了拦截器，
默认拦截器就会失去作用，如果想不让他失去作用，
也必须显式地定义系统默认的拦截器。
</ interceptors > < default-interceptor-ref name ="defaultStack" /> < default-class-ref class ="com.opensymphony.xwork2.ActionSupport" /> </ package >
“defaultStack”和“paramsPrepareParamsStack”拦截器栈都提供了拦截器大部分功能
只是拦截顺序不一样。一般情况下会使用前者，但是某些涉及参数传递和取值的问题
例如实现了ModelDriven接口的某些时候，使用后者，就不用自己再额外编写拦截器类了
defaultStack
< interceptor-stack name ="defaultStack" > < interceptor-ref name ="exception" /> < interceptor-ref name ="alias" /> < interceptor-ref name ="servletConfig" /> < interceptor-ref name ="i18n" /> < interceptor-ref name ="prepare" /> < interceptor-ref name ="chain" /> < interceptor-ref name ="debugging" /> < interceptor-ref name ="scopedModelDriven" /> < interceptor-ref name ="modelDriven" /> < interceptor-ref name ="fileUpload" /> < interceptor-ref name ="checkbox" /> < interceptor-ref name ="multiselect" /> < interceptor-ref name ="staticParams" /> < interceptor-ref name ="actionMappingParams" /> < interceptor-ref name ="params" > < param name ="excludeParams" > dojo\..*,^struts\..* </ param > </ interceptor-ref > < interceptor-ref name ="conversionError" /> < interceptor-ref name ="validation" > < param name ="excludeMethods" > input,back,cancel,browse </ param > </ interceptor-ref > < interceptor-ref name ="workflow" > < param name ="excludeMethods" > input,back,cancel,browse </ param > </ interceptor-ref > </ interceptor-stack >
paramsPrepareParamsStack
< interceptor-stack name ="paramsPrepareParamsStack" > < interceptor-ref name ="exception" /> < interceptor-ref name ="alias" /> < interceptor-ref name ="i18n" /> < interceptor-ref name ="checkbox" /> < interceptor-ref name ="multiselect" /> < interceptor-ref name ="params" > < param name ="excludeParams" > dojo\..*,^struts\..* </ param > </ interceptor-ref > < interceptor-ref name ="servletConfig" /> < interceptor-ref name ="prepare" /> < interceptor-ref name ="chain" /> < interceptor-ref name ="modelDriven" /> < interceptor-ref name ="fileUpload" /> < interceptor-ref name ="staticParams" /> < interceptor-ref name ="actionMappingParams" /> < interceptor-ref name ="params" > < param name ="excludeParams" > dojo\..*,^struts\..* </ param > </ interceptor-ref > < interceptor-ref name ="conversionError" /> < interceptor-ref name ="validation" > < param name ="excludeMethods" > input,back,cancel,browse </ param > </ interceptor-ref > < interceptor-ref name ="workflow" > < param name ="excludeMethods" > input,back,cancel,browse </ param > </ interceptor-ref > </ interceptor-stack >
defaultStack无法接收prepare()需要的数据，而应借助paramsPrepareParamsStack拦截器栈
使用prepare拦截器之前，应先调用params拦截器，prepare() 才能接收到表单数据
基于这个思路，可以通过各种手段将params拦截器放置在prepare拦截器之前即可
比如将defaultStack中的所有拦截器拷贝到struts.xml的我们自定义的myStack拦截器栈中
再按照paramsPrepareParamsStack拦截器栈中的params和prepare顺序修改二者位置即可