jsp提交数据为null,不知原因,请教?
下面是页面
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%@ page language="java" import="java.util.*" pageEncoding="GB2312"%>
<%
	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>电表信息设置</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">
	-->
		<script type="text/javascript">     
		  function mysubmit(type){
		    ammeterInfo.action = ammeterInfo.action + type ;
		  }
	  </script>
	</head>
	<body>
		<table width="80%" border="1" align="center"
			bordercolor="#99CCFF">
			<tbody>
				<tr>
					<td width="5%">
						 
					</td>
					<td width="24%" height="5%" align="center" valign="middle">
						 电表类型
					</td>
					<td width="24%" height="5%" align="center" valign="middle">
						 电表名称
					</td>
					<td width="23%" height="5%" align="center" valign="middle">
						 生产厂家
					</td>
					<td width="24%" height="5%" align="center" valign="middle">
						 电表常数
					</td>
					<td width="24%" height="5%" align="center" valign="middle">
						 表安培数
					</td>
					<td width="24%" height="5%" align="center" valign="middle">
						 表电压数
					</td>
					<td width="24%" height="5%" align="center" valign="middle">
						 电表相数
					</td>
					<td width="24%" height="5%" align="center" valign="middle">
						 过载倍数
					</td>
					<td width="24%" height="5%" align="center" valign="middle">
						 型号版本
					</td>
				</tr>
				<c:forEach var="ammeter" items="${listInfo}">
					<tr>
						<td>
							 
							<input type="checkbox" name="id" value="${ammeter.电表类型}" />
						</td>
						<td width="24%" height="5%" align="center" valign="middle">
							 ${ammeter.电表类型}
						</td>
						<td width="24%" height="5%" align="center" valign="middle">
							 ${ammeter.电表名称}
						</td>
						<td width="23%" height="5%" align=