1 ActionForm中的validate方法验证
1)重写ActionForm中的validate方法
public ActionErrors validate(ActionMapping mapping,HttpServletRequest request){
 ActionErrors errors=new ActionErrors ();
  if(username==null || username.length()<0){
  errors.add("unameisnull",new ActionMessgae("error.validate.unull"));
 }
 return errors;
}
2)资源文件ApplicationResources.properties
error.validate.unull=usernaem is null
3)在config.xml的<action-mappings>中<action>加入validate="true"属性
4)页面标签
<html:errors/>
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validate验证框架
1 创建form继承ValidatorForm或用DynaValidatorForm
2 在WEB-INF下创建validator-rules.xml和validation.xml
3 在src下创建资源文件ApplicationResources.properties
4 要struts-config.xml中配
<plug-in className="org.apache.struts.validator.ValidatorPlugIn">
    <set-property property="pathnames"
                       value="/WEB-INF/validator-rules.xml,/WEB-INF/validation.xml"/>
</plug-in>
5 编写validation.xml文件
<formset>
 <form name="userForm">
   <field property="username"  depends="required">
   <arg key="lable.username"/>
   </field>
 </form>
</formset>
6 页面使用<html:errors/>标签