此URL不支持Http方法GET

我用dopost方法就进不去我的注册界面，用doGet方法就进不去注册成功后跳转的界面；
求帮我看下，大谢。

package com.example.book.web;

import com.example.book.Pojo.User;
import com.example.book.service.UserService;
import com.example.book.service.impl.UserServiceImpl;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class RegistServlet extends HttpServlet {
    private UserService userService=new UserServiceImpl();
    @Override
    //因为注册有密码不想让别人看见所以用dopost请求
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1.获取请求参数
       String username=req.getParameter("username");
       String password=req.getParameter("password");
       String email=req.getParameter("email");
       String code=req.getParameter("code");
       //2.检查验证码是否正确
        if("123456".equalsIgnoreCase(code)){
            //正确
            // 3.检查用户名是否可用
            if(userService.existsUsername(username)){
                //不可用
                System.out.println("用户名["+username+"]已存在！");
                //跳回注册界面
                req.getRequestDispatcher("/pages/user/regist.jsp").forward(req,resp);
            }else {
                //可用
                //调用Service保存到数据库
                userService.registUser(new User(null,username,password,email));
                //跳到注册成功界面
                req.getRequestDispatcher("/pages/user/regist_success.jsp").forward(req,resp);
            }

        }else {
            //不正确
            //跳回注册页面
            System.out.println("验证码["+code+"]错误");
            req.getRequestDispatcher("/pages/user/regist.jsp").forward(req,resp);
        }

    }
}

跨域了？