java.lang.NumberFormatException:For input string - struts

jsp页面:   
  <%@ page language="java" contentType="text/html;charset=gbk"%>
  <%@include file="/taglibs.jsp" %>
  <%
  String id=request.getParameter("id");
  String password=request.getParameter("password");
  String realName=request.getParameter("realName");
  String mark=request.getParameter("mark");
 
 
  if(id==null || password==null||realName==null || mark==null)
  return;
  realName=new String(realName.getBytes("iso-8859-1"),"gbk");
  mark=new String(mark.getBytes("iso-8859-1"),"gbk");
  out.println(id);
  out.println(password);
  out.println(realName);
  out.println(mark);
  %>
  <html:form action="bMainChange.do">
  <table border=1 >
  <tr>
  <td>帐号:</td>
  <html:hidden property="id"/>
  <td width=300><html:text property="name"/></td>
  </tr>
  <tr>
  <td>密码:</td>
  <td width=300><html:text property="password" /></td>
  </tr>
  <tr>
  <td>真实姓名:</td>
  <td width=300><html:text property="realName" value="id"/></td>
  </tr>
  <tr>
  <td>管理员类型:</td>
  <td width=300>一般管理员</td>
  </tr>
  <tr>
  <td><html:submit value="修改" /></td>
  <td width=300><html:reset value="重置"/></td>
  </tr>
  <tr>
  <td><a href="javascript:history.back();">返回</a></td>
  </tr>
  </table>
  </html:form>
  ====================================================================   
action:   
  /*
  * Generated by MyEclipse Struts
  * Template path: templates/java/JavaClass.vtl
  */
  package com.yourcompany.struts.action;
 
  import hibernate.HibernateSessionFactory;
 
  import java.util.List;
 
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import javax.servlet.http.HttpSession;
 
  import org.apache.struts.action.Action;
  import org.apache.struts.action.ActionForm;
  import org.apache.struts.action.ActionForward;
  import org.apache.struts.action.ActionMapping;
  import org.hibernate.Query;
  import org.hibernate.Session;
  import org.hibernate.Transaction;