servlet没有进去，怎么解决啊，88888没有打印在控制台，没有进去servlet，这是为什么啊，怎么解决呢

问题遇到的现象和发生背景

问题相关代码，请勿粘贴截图

运行结果及报错内容

我的解答思路和尝试过的方法

我想要达到的结果

//RegistServlet.java文件

package com.rain.web;
import com.rain.pojo.User;
import com.rain.service.impl.UserService;
import com.rain.service.impl.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
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException, IOException {
        System.out.println("88888");
        //  1、获取请求的参数

        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  === 写死,要求验证码为:abcde
        if ("abcde".equalsIgnoreCase(code)) {
//        3、检查 用户名是否可用
            if (userService.existsUsername(username)) {
                System.out.println("用户名[" + username + "]已存在!");
//        跳回注册页面
                req.getRequestDispatcher("pages/user/regist.html").forward(req, resp);
            } else {
                //      可用
//                调用Sservice保存到数据库
                userService.registUser(new User(null, username, password, email));
//
//        跳到注册成功页面 regist_success.html
                req.getRequestDispatcher("pages/user/regist_success.html").forward(req, resp);
            }
        } else {
            System.out.println("验证码[" + code + "]错误");
            req.getRequestDispatcher("pages/user/regist.html").forward(req, resp);
        }
    }
}

//regist.html文件
<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>书城注册页面</title>
    <base href="http://localhost:63342/JavaWeb/Book/web/pages/user/">

    <link type="text/css" rel="stylesheet" href="../../static/css/style.css">
    <script type="text/javascript" src="../../static/script/jquery-1.7.2.js"></script>
    <script type="text/javascript">
        //页面加载完毕

        $(function () {

            //给注册按钮绑定点击事件
            $("#sub_btn").click(function () {
                //验证用户名，密码，确认密码，电子邮件，验证码

                //用户名
                var usernameText = $("#username").val();
                var usernamePatt = /^\w{5,12}$/;
                if (!usernamePatt.test(usernameText)) {
                    $("span.errorMsg").text("用户名不合法！");
                    return false;
                }

                //密码
                var passwordText = $("#password").val();
                var passwordPatt = /^\w{5,12}$/;
                if (!passwordPatt.test(passwordText)) {
                    $("span.errorMsg").text("密码不合法！");
                    return false;
                }

                //确认密码
                var repwdText = $("#repwd").val();
                if (passwordText != repwdText) {
                    $("span.errorMsg").text("确认密码和密码不一致！");
                    return false;

                }

                //电子邮箱
                var emailText = $("#email").val();
                var emailPatt = /^\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*$/;

                if (!emailPatt.test(emailText)) {
                    $("span.errorMsg").text("邮箱不合法！");
                    return false;
                }

                //验证码
                var codeText = $("#code").val();
                //去掉验证码前后的空格
                codeText = $.trim(codeText);
                if (codeText == null || codeText == "") {
                    $("span.errorMsg").text("验证码不能为空！");
                    return false;
                }
                $("span.errorMsg").text("");

            })

        })
    </script>
    <style type="text/css">
        .login_form {
            height: 420px;
            margin-top: 25px;
        }

    </style>
</head>
<body>


<div class="login_banner">

    <div id="l_content">
        <span class="login_word">欢迎注册</span>
    </div>

    <div id="content">
        <div class="login_form">
            <div class="login_box">
                <div class="tit">
                    <h1>注册书城会员</h1>
                    <span class="errorMsg"></span>
                </div>
                <div class="form">

                    <form action="RegistServlet" method="post">

                        <label>用户名称：</label>
                        <input class="itxt" type="text" placeholder="请输入用户名" autocomplete="off" tabindex="1"
                               name="username" id="username" value="wy6666"/>
                        <br/>
                        <br/>
                        <label>用户密码：</label>
                        <input class="itxt" type="password" placeholder="请输入密码" autocomplete="off" tabindex="1"
                               name="password" id="password" value="123456"/>
                        <br/>
                        <br/>
                        <label>确认密码：</label>
                        <input class="itxt" type="password" placeholder="确认密码" autocomplete="off" tabindex="1"
                               name="repwd" id="repwd" value="123456"/>
                        <br/>
                        <br/>
                        <label>电子邮件：</label>
                        <input class="itxt" type="text" placeholder="请输入邮箱地址" autocomplete="off" tabindex="1"
                               name="email" id="email" value="12345654321@163.com"/>
                        <br/>
                        <br/>
                        <label>验证码：</label>
                        <input class="itxt" type="text" style="width: 150px;" id="code" name="code" value="abcde"/>
                        <img alt="" src="../../static/img/code.bmp" style="float: right; margin-right: 40px">
                        <br/>
                        <br/>
                        <input type="submit" value="注册" id="sub_btn"/>

                    </form>
                </div>

            </div>
        </div>
    </div>
</div>

</body>
</html>

//web.xml文件：
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
    <servlet>
        <servlet-name>RegistServlet</servlet-name>
        <servlet-class>com.rain.web.RegistServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>RegistServlet</servlet-name>
        <url-pattern>/RegistServlet</url-pattern>
    </servlet-mapping>

</web-app>