一个简单servlet+jsp+javabean报错 405 HTTP method POST is not supported by this URL

本人菜鸟，求高手帮帮忙。要做毕业设计了。。。。。

CheckAdmin:
package com.tyhg.action;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class CheckAdmin extends HttpServlet{

protected void processRequest(HttpServletRequest request,HttpServletResponse response) throws IOException,ServletException{
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
String name = request.getParameter("username");
String pass = request.getParameter("password");
if(name.equalsIgnoreCase("admin") && pass.equals("12345")){
response.sendRedirect("http://www.baidu.com");
}
else{
response.sendRedirect("http://www.baidu.com");
}
out.close();
}

protected void doPost(HttpServletResponse response,HttpServletRequest request) throws IOException,ServletException{
processRequest(request,response);
}
protected void doGet(HttpServletResponse response,HttpServletRequest request) throws IOException,ServletException{
doPost(request,response);
}
}

web.xml:
<servlet>
<servlet-name>CheckAdmin</servlet-name>
<servlet-class>com.tyhg.action.CheckAdmin</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>CheckAdmin</servlet-name>
<url-pattern>/CheckAdmin</url-pattern>
</servlet-mapping>
jsp:
<form action="CheckAdmin" method="post" id="login" name="login" onsubmit="JavaScript: return check_Null();">