菜鸟求解答……

想用SSH写个列车查询，技术很菜……求指点0-0
刚开始就卡壳了……
写“车次查询”这个功能，就是输入个车次，出现该车次的始发、终点、车型，可是老是出现500错误，新手求教；
JSP：<%@ page language="java" import="java.util.*,com.train.Model.*" pageEncoding="UTF-8"%>
<%@ taglib prefix="s" uri="/struts-tags"  %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<%
TrainMain trainmain = new TrainMain();
 %><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'QTrainId.jsp' starting page</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>
     <s:form action="actions/QBid.action?trainmain.tid=%{#trainmain.tid}"  method="post">
     <s:textfield name="trainmain.tid"  label="车次"></s:textfield>
     <s:submit value="查询"></s:submit>
     </s:form>
  </body>
</html>
Action：package com.train.action;import java.util.Map;import org.springframework.beans.factory.BeanFactory;
import org.springframework.context.support.ClassPathXmlApplicationContext;import com.opensymphony.xwork2.ActionContext;
import com.opensymphony.xwork2.ActionSupport;
import com.train.Model.TrainMain;
import com.train.Model.TrainMainDAO;public class QBidAction extends ActionSupport
{
/**
 * @return the trainmain
 */
public TrainMain getTrainmain()
{
return trainmain;
} /**
 * @param trainmain the trainmain to set
 */
public void setTrainmain(TrainMain trainmain)
{
this.trainmain = trainmain;
} /**
 * @return the message
 */
public String getMessage()
{
return message;
} /**
 * @param message the message to set
 */
public void setMessage(String message)
{
this.message = message;
} private TrainMain trainmain;
private String message; /**
 * @return
 */
public String execute() throws Exception
{
BeanFactory factory = new ClassPathXmlApplicationContext("applicationContext.xml");
TrainMainDAO dao = (TrainMainDAO)factory.getBean("TrainMainDAO");
Map request = (Map)ActionContext.getContext().get("request"); trainmain =  (TrainMain) dao.findByTid(trainmain.getTid());
request.put("list", dao.findById(trainmain.getId()));

// TODO Auto-generated method stub
return SUCCESS;
}
}list1页面:<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@taglib prefix="s"  uri="/struts-tags" %>
<%
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>My JSP 'list1.jsp' starting page</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>
   <table border="1" width="80%"  align="center">
   <tr>
   <td>车次</td>
   <td>始发</td>
   <td>终点</td>
   <td>车型</td>
   </tr>
   
   <s:iterator value="#request.list" id="train">
<tr>
<td>
<s:property value="#train.tid"/>
</td>
<td>
<s:property value="#train.start"/>
</td>
<td>
<s:property value="#train.over"/>
</td>
<td>
<s:property value="#train.kind"/>
</td>
</tr>   
   </s:iterator>
   
   
   </table>
  </body>
</html>
最后显示的是500错误……
The server encountered an internal error () that prevented it from fulfilling this request.