小弟我写了个JSP的登录页面，老是提交不过去，大家帮忙看看了多谢

我写了个JSP的登录页面，老是提交不过去，大家帮忙看看了谢谢
登录页面就不写了logOn.jsp提交给LoginServlet.java
LoginServlet.java代码：
package   com.gsi.role.servlet;

import   java.io.IOException;
import   java.sql.Connection;
import   java.sql.ResultSet;
import   java.sql.SQLException;
import   java.sql.Statement;

import   javax.servlet.ServletException;
import   javax.servlet.http.HttpServletRequest;
import   javax.servlet.http.HttpServletResponse;

import   com.gsi.role.db.ConnectionPool;
import   com.gsi.role.db.DB;

/**
  *   Servlet   implementation   class   for   Servlet:   LoginServlet
  */
public   class   LoginServlet   extends   javax.servlet.http.HttpServlet   implements
javax.servlet.Servlet   {
/*
  *   (non-Java-doc)
  *  
  *   @see   javax.servlet.http.HttpServlet#HttpServlet()
  */
public   LoginServlet()   {
super();
}

/*
  *   (non-Java-doc)
  *  
  *   @see   javax.servlet.http.HttpServlet#doGet(HttpServletRequest   request,
  *             HttpServletResponse   response)
  */
protected   void   doGet(HttpServletRequest   request,
HttpServletResponse   response)   throws   ServletException,   IOException   {
//   TODO   Auto-generated   method   stub
}

/*
  *   (non-Java-doc)
  *  
  *   @see   javax.servlet.http.HttpServlet#doPost(HttpServletRequest   request,
  *             HttpServletResponse   response)
  */
protected   void   doPost(HttpServletRequest   request,
HttpServletResponse   response)   throws   ServletException,   IOException   {
response.setContentType( "text/html ");
String   result   =   " ";

//   获取提交的用户名：
String   strUserName   =   request.getParameter( "C_Usr_Id ");
//   获取提交的密码：
String   strPassword   =   request.getParameter( "C_Usr_Passwd ");
if   ((strUserName   ==   null)   ||   (strUserName.equals( " "))
||   (strUserName.length()   >   20))   {
result   =   "请输入用户名(不超过20字符) ";
request.setAttribute( "error_username ",   result);
response.sendRedirect( "logOn.jsp ");
}
if   ((strPassword   ==   null)   ||   (strPassword.equals( " "))
||   (strPassword.length()   >   20))   {
result   =   "请输入密码(不超过20字符) ";
request.setAttribute( "error_password ",   result);
response.sendRedirect( "logOn.jsp ");
}
//   创建数据库连接对象：
ConnectionPool   connPool   =   DB.getConnPool();
Connection   conn   =   connPool.getConnection();
Statement   stmt   =   null;
ResultSet   rs   =   null;
String   sql= " ";

try   {
//   sql语句：
sql   =   "select   *   from   sys_usr   where   C_Usr_Id= ' "+   strUserName   +   " '   and   C_Usr_Passwd= ' "   +   strPassword   +   " ' ";