By default, the methods input, back, cancel, and browse are excluded from validation. These method names are provided as a parameter to the validation interceptor as configured in the struts-default package. To change the excluded methods, we just need to change the parameter.

<action name=xxx>
<interceptor-ref name="defaultStack">
<param name="validation.excludeMethods">method1,method2</param>
</interceptor-ref>
</action>