输入名字密码之后点击注册出现如下界面

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>用户注册</title>
<link href="style/common.css" type="text/css" rel="stylesheet">
<link href="style/add.css" type="text/css" rel="stylesheet">
<link rel="stylesheet" href="style/login.css">
<script type="text/javascript">
  function validate_form(){
   // 获得用户名的值
   var username = document.getElementById("username").value;
   if(username == null || username==""){
    alert("用户名不能为空");
    return false;
   }
   // 获得密码的值
   var password = document.getElementById("password").value;
   if(password == null || password==""){
    alert("密码不能为空");
    return false;
   }
   // 获得确认密码的值
   var repassword = document.getElementById("repassword").value;
   if(repassword != password){
    alert("两次密码输入不一致");
    return false;
   }
   return true;
  }
</script>
</head>
<body>
<%@ include file="header.jsp" %>

<div class="content">
<div class="center">
    <div class="center-login">
      <div class="login-banner">
       <a href="#"><img src="image/login_banner.png" alt=""></a>
     </div>
     <div class="user-login">
       <div class="user-box">
         <div class="user-title">
           <p>用户注册</p>
         </div>
         <form id="regForm" enctype="multipart/form-data" onsubmit="return validate_form()" class="login-table" action="${pageContext.request.contextPath }/RegistServlet" method="post">
          <div class="login-left">
            <label class="username">用户名&nbsp&nbsp&nbsp&nbsp</label>
            <input type="text" id="username" class="yhmiput" name="username">
          </div>
          <div class="login-left">
            <label class="username">密码&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp</label>
            <input type="password" id="password" class="yhmiput" name="password">
          </div>
    <div class="login-left">
            <label class="username">确认密码</label>
            <input type="password" id="repassword" class="yhmiput" name="repassword">
          </div>
    <div class="login-left">
            <label class="username">上传头像</label>
            <input type="file" class="yhmiput" name="file">
          </div>
    <%-- <div class="login-left">
            <label class="username">验证码&nbsp&nbsp&nbsp&nbsp</label>
            <input type="text" class="codeiput" name="checkCode">
   <img id="codeImg" onclick="changeImg()" src="${pageContext.request.contextPath }/CheckImgServlet">
          </div> --%>

        <div class="login-btn"><button>注册</button></div>
        </form>
      </div>
    </div>
</div>
</div>
</div>
<div class="footer">
<p><span>M-GALLARY</span> ©2017 POWERED BY IMOOC.INC</p>
</div>

</body>
</html>

package com.imooc.domain;

public class User {
private String name;
private String password;
private String path;
public String getName() {
  return name;
}
public void setName(String name) {
  this.name = name;
}
public String getPassword() {
  return password;
}
public void setPassword(String password) {
  this.password = password;
}
public String getPath() {
  return path;
}
public void setPath(String path) {
  this.path = path;
}
public User(String name, String password, String path) {
  super();
  this.name = name;
  this.password = password;
  this.path = path;
}
public User(){

}
@Override
public String toString() {
  return "User [name=" + name + ", password=" + password + ", path=" + path + "]";
}

}

package com.imooc.service;

import java.util.List;

import com.imooc.domain.User;
//import com.sun.xml.internal.bind.v2.schemagen.xmlschema.List;

public interface UserService {
public void regist(List<User> list,User user);

}

package com.imooc.service.impl;

import java.util.List;

import com.imooc.domain.User;
import com.imooc.service.UserService;

public class UserServiceImpl implements UserService{

@Override
public void regist(List<User> list, User user) {
// 保存用户信息
list.add(user);
}

}

package com.imooc.web.listener;

import java.util.ArrayList;
import java.util.List;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

import com.imooc.domain.User;

@WebListener
public class InitServletContextListener implements ServletContextListener {

public void contextDestroyed(ServletContextEvent sce) {
}

    public void contextInitialized(ServletContextEvent sce) {
    System.out.println("项目中数据初始化了....");
    // 创建一个用于保存用户信息的List集合
    List<User> userList = new ArrayList<User>();
    // 将List集合存入到ServletContext域中
    sce.getServletContext().setAttribute("userList", userList);
    }

}

package com.imooc.web.servlet;

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

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

import com.imooc.domain.User;
import com.imooc.service.UserService;
import com.imooc.service.impl.UserServiceImpl;

@WebServlet("/RegistServlet")
public class RegisterServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

protected void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  request.setCharacterEncoding("utf-8");
  response.setContentType("text/html;charset=utf-8");
  //接受数据
  String username = request.getParameter("username");
     String password = request.getParameter("password");
  //封装数据
  User user = new User();
  user.setName(username);
  user.setPassword(password);


  //处理数据
  UserService userService=new UserServiceImpl();
  //从ServletContext域中获取用户的集合
  List<User> list=(List<User>)getServletContext().getAttribute("userList");
  userService.regist(list, user);
System.out.println(list);
response.sendRedirect(request.getContextPath()+"/login.jsp");