<form action="hidden-uploadAttachment.action" method="post" enctype="multipart/form-data">
  <input name="file" type="file"   style="padding:0px; " 
  <input type="submit" value="上传附件" name="agree"/>
</form>

<action name="hidden-uploadAttachment" class="com.ntsky.bbs.web.webwork.action.attachment.UploadAttachmentAction">
            <interceptor-ref name="commonStack"/>
            <interceptor-ref name="basicStack"/>
            <result name="success">/hidden-uploadAttachment.jsp</result>
           </action>

public class UploadAttachmentAction extends AttachmentActionSupport{
          public String execute(){
        if(logger.isDebugEnabled()){
            logger.debug("该代码被执行...");
        }
               //..........上传代码省略
           }