Struts 校验失败 值丢失
struts.xml配置

<package name="default" extends="struts-default">   xxxxx</package>

. 其中,struts-default包含了struts2默认的拦截器栈.

<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="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\..*,^session\..*,^request\..*,^application\..*,^servlet(Request|Response)\..*,parameters\...*</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-ref name="debugging"/>            </interceptor-stack>

该配置在struts2-core.jar的struts-default.xml文件里.

值丢失原因：
当到conversionError Interceptor类型转换失败时，会添加校验失败信息。

if(action instanceof ValidationAware)                {                    ValidationAware va = (ValidationAware)action;                    va.addFieldError(propertyName, message);                }

当conversionError Interceptor执行完，到workflow Interceptor时，如果发现有校验错误信息，直接return "input"给struts，就不会再到你的Action里面，导致值丢失。

解决办法：
配置自己的拦截器栈，去除workflow Interceptor。
<interceptors>
<interceptor-stack name="xxx">
<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="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\..*,^session\..*,^request\..*,^application\..*,^servlet(Request|Response)\..*,parameters\...*</param>
</interceptor-ref>
<interceptor-ref name="conversionError"/>
<interceptor-ref name="validation">
<param name="excludeMethods">input,back,cancel,browse</param>
</interceptor-ref>
</interceptor-stack>
</interceptors>

<default-interceptor-ref name="xxx" />

或者想办法在到达workflow Interceptor之前，把你要的值放进struts2的value stack.

struts流程参考
http://hi.baidu.com/hyy_lover/item/4b26c10e3afc0875d45a11f8