while(rs.next())处出错

while(rs.next())处出错 求助
<%MysqlDB db = Config.inst().db; %>

<form method="post">

<p> 查询日期:<input type="text" name="created_st" value="yyyy-mm-dd">到
<input type="text" name="created_et" value="yyyy-mm-dd">
<input type="submit" value="查询"></p>
</form> 
<table border=1 width=400 class=data>
<tr><th>ID</th><th>姓名</th><th>充值总额(元)</th><th>充值前总额(元)</th><th>充值后总额(元)</th><th>日期</th></tr>
<tr>


<% String starttime = request.getParameter("created_st");
String endtime = request.getParameter("created_et");
ResultSet rs = db.query ("SELECT * FROM payments WHERE creat_at>'starttime' and creat_at<'endtime' ORDER BY creat_at");
while(rs.next()){
  %>
  <tr>
  <td><%=rs.getString(1)%></td>
  <td><%=rs.getString(2)%></td>
  <td><%=rs.getString(3)%></td>
  <td><%=rs.getString(4)%></td>
  <td><%=rs.getString(5)%></td>
  </tr>
  <%
  }
  %>

</table>
  



org.apache.jasper.JasperException: An exception occurred processing JSP page /admin/payments.jsp at line 24

21: <% String starttime = request.getParameter("created_st");
22: String endtime = request.getParameter("created_et");
23: ResultSet rs = db.query ("SELECT * FROM payments WHERE creat_at>'starttime' and creat_at<'endtime' ORDER BY creat_at");
24: while(rs.next()){
25: %>
26: <tr>
27: <td><%=rs.getString(1)%></td>


Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:568)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)


root cause 

java.lang.NullPointerException
org.apache.jsp.admin.payments_jsp._jspService(payments_jsp.java:140)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)


------解决方案--------------------
ResultSet rs = db.query ("SELECT * FROM payments WHERE creat_at>'"+ starttime + "' and creat_at<'"+ endtime + "' ORDER BY creat_at");

ResultSet中的SQL应该是上面的样子吧 ？

加以判断来控制空指针 ：--->
if (rs != null){
while(rs.next()){
...
}
}
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