求助，numberformat报错尝试了很多次也没解决

<%@ page language="java" contentType="text/html; charset=gbk"
    pageEncoding="gbk"%>
<%@ page import="java.sql.*" %><%
Class.forName("com.mysql.jdbc.Driver");
String url = "jdbc:mysql://localhost/work?user=root&password=root";
Connection conn = DriverManager.getConnection(url);int id = Integer.parseInt(request.getParameter("id"));
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("select * from content where id=" + id);request.setCharacterEncoding("gbk");
String action = request.getParameter("action");if(action != null && action.equals("modify")) {
String week = request.getParameter("week");
String saturday = request.getParameter("saturday");
String sunday = request.getParameter("sunday");
String monday = request.getParameter("monday");
String tuesday = request.getParameter("tuesday");
String wednesday = request.getParameter("wednesday");
String thursday = request.getParameter("thursday");
String friday = request.getParameter("friday");
String nextweek = request.getParameter("nextweek");
String needhelp = request.getParameter("needhelp");
String workplace = request.getParameter("workplace");


conn.setAutoCommit(false);

String sql = "update content set saturday = ? , sunday = ?, monday = ?, tuesday = ?,wednesday = ?,thursday = ?,friday = ?,nextweek = ?,needhelp = ?,workplace = ? where id = ?";
PreparedStatement pstmt = conn.prepareStatement(sql);
Statement stmt1 = conn.createStatement();

pstmt.setString(1, saturday);
pstmt.setString(2, sunday);
pstmt.setString(3, monday);
pstmt.setString(4, tuesday);
pstmt.setString(5, wednesday);
pstmt.setString(6, thursday);
pstmt.setString(7, friday);
pstmt.setString(8, nextweek);
pstmt.setString(9, needhelp);
pstmt.setString(10, workplace);
pstmt.setInt(11, id);
pstmt.executeUpdate();
conn.commit();
conn.setAutoCommit(true);

stmt.close();
stmt1.close();
pstmt.close();
conn.close();

response.sendRedirect("ShowWork.jsp");
}
%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gbk">
<link href="images/main.css" rel="stylesheet"
type="text/css">
<title>Insert title here</title>
</head>
<body>
<%
if(rs.next()) {
%>
<form action="modify.jsp" method="post">
<input type="hidden" name="action" value="modify">
<table width="99%" border="0" align="center" cellpadding="0"
cellspacing="1" class="tableMain">
<tr>
<td align="center" colspan="5" class="tableHead">添加新的工作计划表</td>
</tr>
<TR class="inputTableCell">
<TD width="20%" align="left" class="tableHeadLeft">第几周(阿拉伯数字)</TD>
</TD>

</TR>
<tr align="left" >
<td>
<textarea  cols="100" rows="1" name="week"><%= rs.getString("week") %></textarea>
</td>
</tr>
<TR class="inputTableCell">
<TD width="20%" align="left" class="tableHeadLeft">部门:</TD>
</TD>

</TR>
<tr align="left" >
<td>
<textarea  cols="100" rows="1" name="workplace"><%= rs.getString("workplace") %></textarea>
</td>
</tr>
<TR class="inputTableCell">
<TD width="20%" align="left" class="tableHeadLeft">星期六：</TD>
</TD>

</TR>
<tr align="left" >
<td>
<textarea  cols="100" rows="3" name="saturday"><%= rs.getString("saturday") %></textarea>
</td>
</tr>
<TR class="inputTableCell">
<TD width="20%" align=""left"" class="tableHeadLeft">星期日：</TD>
</TD>

</TR>
<tr align="left" >
<td>
<textarea  cols="100" rows="3" name="sunday"><%= rs.getString("sunday") %></textarea>
</td>
</tr>
<TR class="inputTableCell">
<TD width="20%" align=""left"" class="tableHeadLeft">星期一：</TD>
</TD>

</TR>
<tr align="left" >
<td>
<textarea  cols="100" rows="3" name="monday"><%= rs.getString("monday") %></textarea>
</td>
</tr>
<TR class="inputTableCell">
<TD width="20%" align=""left"" class="tableHeadLeft">星期二：</TD>
</TD>

</TR>
<tr align="left" >
<td>
<textarea  cols="100" rows="3" name="tuesday"><%= rs.getString("tuesday") %></textarea>
</td>
</tr>
<TR class="inputTableCell">
<TD width="20%" align=""left"" class="tableHeadLeft">星期三：</TD>
</TD>

</TR>
<tr align="left" >
<td>
<textarea  cols="100" rows="3" name="wednesday"><%= rs.getString("wednesday") %></textarea>
</td>
</tr>
<TR class="inputTableCell">
<TD width="20%" align="left" class="tableHeadLeft">星期四：</TD>
</TD>

</TR>
<tr align="left" >
<td>
<textarea  cols="100" rows="3" name="thursday"><%= rs.getString("thursday") %></textarea>
</td>
</tr>
<TR class="inputTableCell">
<TD width="20%" align="left" class="tableHeadLeft">星期五：</TD>
</TD>

</TR>
<tr align="left" >
<td>
<textarea  cols="100" rows="3" name="friday"><%= rs.getString("friday") %></textarea>
</td>
</tr>
<TR class="inputTableCell">
<TD width="20%" align="left" class="tableHeadLeft">下周工作计划：</TD>
</TD>

</TR>
<tr align="left" >
<td>
<textarea  cols="100" rows="3" name="nextweek"><%= rs.getString("nextweek") %></textarea>
</td>
</tr>
<TR class="inputTableCell">
<TD width="20%" align="left" class="tableHeadLeft">需要请示的工作：</TD>
</TD>

</TR>
<tr align="left" >
<td>
<textarea  cols="100" rows="3" name="needhelp"><%= rs.getString("needhelp") %></textarea>
</td>
</tr>

<td align="left">
<input type="submit" value="提交">
</td>
</tr>
</table>

</form>
<%
}
%>
</body>
</html>
问题是：每次我进入修改界面，就是此界面，一提交就报错，java.lang.NumberFormatException: null
java.lang.Integer.parseInt(Unknown Source)
java.lang.Integer.parseInt(Unknown Source)
我认为是id那里有问题，但是没解决，麻烦各位大侠帮忙看看