struts2+hibernate整合，出现空指针错误

XsAction：

package org.action;

import java.io.File;
import java.io.FileInputStream;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;



import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;

import org.apache.struts2.ServletActionContext;
import org.dao.imp.KcDao;
import org.dao.imp.KcDaoImp;
import org.dao.imp.XsDao;
import org.dao.imp.XsDaoImp;
import org.dao.imp.ZyDao;
import org.dao.imp.ZyDaoImp;
import org.model.*;

import com.opensymphony.xwork2.ActionContext;
import com.opensymphony.xwork2.ActionSupport;

public class XsAction  extends ActionSupport{
	KcDao kcDao;
	XsDao xsDao;
	private Xsb xs;
	private Kcb kcb;
	private File zpFile;
	private Zyb zyb;
	public File getZpFile(){
		return zpFile;
	}
	public void setZpFile(File zpFile){
		this.zpFile=zpFile;
	}
	public Kcb getKcb(){
		return kcb;
	}
	public void setKcb(Kcb kcb){
		this.kcb=kcb;
	}
	public Zyb getZyb(){
		return zyb;
	}
	public void setZyb(Zyb zyb){
		this.zyb=zyb;
	}
	public Xsb getXsb(){
		return xs;
	}
	public void setXsb(Xsb xs){
		this.xs=xs;
	}
	public String execute() throws Exception{
		Map session=(Map)ActionContext.getContext().getSession();
		Dlb user=(Dlb)session.get("user");
		xsDao=new XsDaoImp();
		Xsb xs=xsDao.getOneXs(user.getXh());
		Map request=(Map)ActionContext.getContext().get("request");
		request.put("xs", xs);
		return SUCCESS;

	}
	public String getImage() throws Exception{
		xsDao=new XsDaoImp();
		byte[] zp=xsDao.getOneXs(xs.getXh()).getZp();
		HttpServletResponse response=ServletActionContext.getResponse();
		response.setContentType("image/jpeg");
		ServletOutputStream os=response.getOutputStream();
		if(zp!=null&&zp.length>0){
			for(int i=0;i<zp.length;i++){
				os.write(zp[i]);
			}
		}
		return NONE;

	}
	public String updateXsInfo() throws Exception{
		Map session=(Map)ActionContext.getContext().getSession();
		Dlb user=(Dlb)session.get("user");
		xsDao=new XsDaoImp();
		ZyDao zyDao=new ZyDaoImp();
		List zys=zyDao.getAll();
		Xsb xs=xsDao.getOneXs(user.getXh());
		Map request=(Map)ActionContext.getContext().get("request");
		request.put("zys", zys);
		request.put("xs", xs);
		return SUCCESS;



	}
	public String updateXs() throws Exception{
		xsDao=new XsDaoImp();
		ZyDao zyDao=new ZyDaoImp();
		Xsb stu=new Xsb();
		stu.setXh(xs.getXh());	102行
		Set list=xsDao.getOneXs(xs.getXh()).getKcs();
		stu.setKcs(list);
		stu.setXm(xs.getXm());
		stu.setXb(xs.getXb());
		stu.setCssj(xs.getCssj());
		stu.setZxf(xs.getZxf());
		stu.setBz(xs.getBz());
		Zyb zy=zyDao.getOneZy(zyb.getId());
		stu.setZyb(zy);
		if(this.getZpFile()!=null){
			FileInputStream fis=new FileInputStream(this.getZpFile());
			byte[] buffer=new byte[fis.available()];
			fis.read(buffer);
			stu.setZp(buffer);
		}
		xsDao.update(stu);

		return SUCCESS;

	}
	public String getXsKcs() throws Exception{
		Map session=(Map)ActionContext.getContext().getSession();
		Dlb user=(Dlb)session.get("user");
		xsDao=new XsDaoImp();
		String xh=user.getXh();
		Xsb xsb=xsDao.getOneXs(xh);
		Set list=xsb.getKcs();
		Map request=(Map)ActionContext.getContext().get("request");
		request.put("list", list);
		return SUCCESS;


	}
	public String deleteKc() throws Exception{
		Map session=(Map)ActionContext.getContext().getSession();
		String xh=((Dlb)session.get("user")).getXh();
		xsDao=new XsDaoImp();
		Xsb xs2=xsDao.getOneXs(xh);
		Set list=xs2.getKcs();
		Iterator iter=list.iterator();
		while(iter.hasNext()){
			Kcb kc2=(Kcb)iter.next();
			if(kc2.getKch().equals(kcb.getKch())){
				iter.remove();
			}
		}
		xs2.setKcs(list);
		xsDao.update(xs2);
		return SUCCESS;
	}
	public String selectKc() throws Exception{
		Map session=(Map)ActionContext.getContext().getSession();
		String xh=((Dlb)session.get("user")).getXh();
		xsDao=new XsDaoImp();
		Xsb xs3=xsDao.getOneXs(xh);
		Set list=xs3.getKcs();
		Iterator iter=list.iterator();
		while(iter.hasNext()){
			Kcb kc3=(Kcb)iter.next();
			if(kc3.getKch().equals(kcb.getKch())){
				return ERROR;
			}



		}
	            list.add(new KcDaoImp().getOneKc(kcb.getKch()));

				xs3.setKcs(list);
				xsDao.update(xs3);
				return SUCCESS;



	}

}

struts.xml：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuaration 2.3//EN"
"http://struts.apache.org//dtds/struts-2.3.dtd">


<struts>
<package name="default" extends="struts-default">
   <action name="login" class="org.action.LoginAction">
     <result name="success">/main.jsp</result>
     <result name="error">/login.jsp</result>
   </action>
   <action name="xsInfo" class="org.action.XsAction">
     <result name="success">/xsInfo.jsp</result>
   </action>
   <action name="getImage" class="org.action.XsAction" method="getImage">
   </action>
   <action name="updateXsInfo" class="org.action.XsAction" method="updateXsInfo">
     <result name="success">/updateXsInfo.jsp</result>
   </action>
   <action name="updateXs" class="org.action.XsAction" method="updateXs">
     <result name="success">/updateXs_success.jsp</result>
   </action>
   <action name="getXsKcs" class="org.action.XsAction" method="getXsKcs">
   <result name="success">/xsKcs.jsp</result>
   </action>
   <action name="deleteKc" class="org.action.XsAction" method="deleteKc">
     <result name="success">/deleteKc_success.jsp</result>
   </action>
   <action name="getAllKc" class="org.action.KcAction">
     <result name="success">/allKc.jsp</result>
   </action>
   <action name="selectKc" class="org.action.XsAction" method="selectKc">
     <result name="success">/selectKc_success.jsp</result>
     <result name="error">/selectKc_fail.jsp</result>
   </action>
</package>

</struts>

updateXsInfo。jsp：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib uri="/struts-tags" prefix="s" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>学生选课系统</title>
    
	<meta http-equiv="pragma" content="no-cache">
	<meta http-equiv="cache-control" content="no-cache">
	<meta http-equiv="expires" content="0">    
	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->

  </head>
  
  <body bgcolor="#D9DFAA">
    <s:set name="xs" value="#request.xs"></s:set>
    <s:form action="updateXs.action" method="post" enctype="multipart/form-data">
    <table>
    <tr>
       <td>学号:</td>
       <td><input type="text" name="xs.xh" value="<s:property value="#xs.xh"/>"readonly/>
    </td></tr>
    <tr>
     <td>姓名:</td>
     <td><input type="text" name="xs.xm" value="<s:property value="#xs.xm"/>"/></td>
   </tr>
   <tr>
     <s:radio list="#{1:""男"",0:""女"" }" value="#xs.xb" name="xs.xb" label="性别"></s:radio>
   </tr>
   <tr>
     <td>专业:</td>
     <td>
     <select name="zyb.id">
       <s:iterator id="zy" value="#request.zys">
         <option value="<s:property value="#zy.id"/>">
           <s:property value="#zy.zym"/></option>
       </s:iterator>
     </select>
     </td>
   </tr>
   <tr>
     <td>出生时间:</td>
     <td><input type="text" name="xs.cssj" value="<s:date name="#xs.cssj" format="yyyy-MM-dd"/>"/></td>
   </tr>
   <tr>
     <td>备注:</td>
     <td><input type="text" name="xs.bz" value="<s:date name="#xs.bz"/>"/></td>
   </tr>
   <tr>
     <td>总学分:</td>
     <td><input type="text" name="xs.zxf" value="<s:property value="#xs.zxf"/>"/></td>
   </tr>
   <tr>
      <td>照片:</td>
      <td><input type="file" name="zpFile"/></td>
   </tr>
   <tr>
     <td><input type="submit" value="修改"/></td>
   </tr>
      
    </table>
 
    </s:form>
    
  </body>
</html>