405错误无法解决，求各位帮忙！
最近消息老是遇到一些很简单的但是无法解决的问难
这次遇到的是type   Status   report

message   HTTP   method   GET   is   not   supported   by   this   URL

description   The   specified   HTTP   method   is   not   allowed   for   the   requested   resource   (HTTP   method   GET   is   not   supported   by   this   URL).

在网上搜的方法大都是xml没配置好，url写错，setvlet里doGet（）方法没有重载之类的，但是我在servlet里面确实写过doGet方法，可是405错误一直出现

链接是这样写的 <a   href= " <%=request.getContextPath()%> /colDemo ">
最早 <a   href= "colDemo "> 也不能解决问题（colDemo是一个servlet）
xml配置完好
<servlet>
        <servlet-name> colDemo </servlet-name>
        <servlet-class> op.colDemo </servlet-class>
    </servlet>


    <servlet-mapping>
        <servlet-name> colDemo </servlet-name>
        <url-pattern> /colDemo </url-pattern>
    </servlet-mapping>

如果大家没有不耐烦，请帮忙看看我写的servlet

package   op;

import   javax.servlet.*;
import   javax.servlet.http.*;
import   javax.servlet.Servlet;
import   java.sql.*;
import   java.io.*;
import   java.util.*;
import   Database.conDB;

public   class   colDemo   extends   HttpServlet{


public   void   init(ServletConfig   config)   throws   ServletException
{
super.init(config);
}



public   void   doGet(HttpServletResponse   response,HttpServletRequest   request)
throws   IOException,ServletException
{

response.setContentType( "text/html;charset=gb2312 ");
PrintWriter   out   =   response.getWriter();
HttpSession   session   =   request.getSession();
conDB   db   =   new   conDB();
String   sql   =   "select   *   from   v_sco_demo ";
ResultSet   rs   =   null;
int   rsLen   =   0;
ArrayList   alDemo   =   new   ArrayList();//以rs.next()存储民主评议分数
ArrayList   alID   =   new   ArrayList();//以rs.nect()存储得到该分数的人的ID
try
{
rs   =   db.Query(sql);
while(rs.next())
{
alDemo.add(rs.getFloat( "sco "));
alID.add(rs.getInt( "beExerID "));
rsLen++;//获取rs长度
}
}
catch(Exception   e)
{
e.printStackTrace();
}

String   sql1   =   " ";
int   iUpdt   =   0;
conDB   db1   =   new   conDB();
try
{
for(int   i   =   0;i <rsLen;i++)
{
sql1   =   "update   total   set   scoDemo= "+alDemo.get(i)+ "where   userID= "+alID.get(i);
iUpdt   =   db1.Update(sql1);
}
if   (iUpdt   ==   0)
out.println( " <script> alert( '汇总失败