老师，这个地方，改成doPost,405错误，说这个方法不被URL所支持，是有什么规定？？？

package com.cl.employee;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class EmpServlet
 */
@WebServlet("/emp")
public class EmpServlet extends HttpServlet {
 private static final long serialVersionUID = 1L;
      
    /**
     * @see HttpServlet#HttpServlet()
     */
    public EmpServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

 /**
  * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
  */
 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  // TODO Auto-generated method stub
  //采用doPost怎么会不允许，什么原因
  request.setCharacterEncoding("UTF-8");
  //使用全局对象ServletContext,让后进行数据初始化操作
  ServletContext context=request.getServletContext();
  if(context.getAttribute("employee")==null) {
   List list=new ArrayList();
   list.add(new Employee(2212,"张小小","开发部","web前端工程师",20000f));
   context.setAttribute("employee", list);
  }  
  request.getRequestDispatcher("/employee.jsp").forward(request,response);
 }
}