Dr. Peking University will take you to decrypt: How to use Java to easily implement authentication services? Xiaobai: It's too simple

Today's sharing starts, please give me more advice~

Most systems today have their own authentication service, which is the first step for users to interact with the system. The system needs a series of steps to understand who you are and what you can do. After understanding these, it can better serve you.

1. What is authentication service

Authentication refers to verifying whether a user has the right to access the system.

Authentication includes two aspects:

User authentication, the network authenticates users to prevent illegal users from occupying network resources.
Network authentication, the user authenticates the network to prevent the user from accessing an illegal network and defrauding key information.

The authentication here mainly refers to user authentication, that is, how to confirm that "you are you". The simplest embodiment is the usual user login and logout.

Second, use servlet+jdbc to implement a simple user login program

1. Clear ideas

First, we have to think carefully about what do we need?

Let us first recall how the general login is done?

For the web page, a login page will appear first, then, enter the account password, click login, and a success/failure page will pop up.

How to judge success/failure?

Think about it, the easiest way is to get the data from the front-end and check it in the data to see if the password is the same, and then reply to the front-end and say - I found it, he is XXX or me Can't find his record, ask him to re-enter the account password.

Then the front end makes corresponding operations on this reply, for example, if the login is successful, it will jump to the home page, and if it fails, the user will re-enter.

2. Teach you how to implement a simple web login program

①Create a web project

Open the idea and create a new web project

Here, in order to facilitate the management of the jar package, select the project of the maven structure, then select to create from the prototype, and select the webapp (this is just for convenience, you can also select an empty project, but it will take some time).

Click Next and enter a project name

Here, select the corresponding maven, and the idea has its own maven and jar package warehouses.

Select to complete, such a simplest project structure comes out.

Next, you need to configure pom.xml, because the jar packages of jdbc and tomcat are used (after all, they are all interfaces that call others)

(Just add it to the project tag), the above configuration means to import two third-party toolkits

②Write a simple login page

Here I want to look good and be lazy, so I use the template of the layui framework

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>后台管理-登陆</title>
    <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
    <meta http-equiv="Access-Control-Allow-Origin" content="*">
    <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1">
    <meta name="apple-mobile-web-app-status-bar-style" content="black">
    <meta name="apple-mobile-web-app-capable" content="yes">
    <meta name="format-detection" content="telephone=no">
    <link rel="stylesheet" href="../lib/layui-v2.6.3/css/layui.css" media="all">
    <!--[if lt IE 9]>
    <script src="https://cdn.staticfile.org/html5shiv/r29/html5.min.js"></script>
    <script src="https://cdn.staticfile.org/respond.js/1.4.2/respond.min.js"></script>
    <![endif]-->
    <style>
        .main-body {top:50%;left:50%;position:absolute;-webkit-transform:translate(-50%,-50%);-moz-transform:translate(-50%,-50%);-ms-transform:translate(-50%,-50%);-o-transform:translate(-50%,-50%);transform:translate(-50%,-50%);overflow:hidden;}
        .login-main .login-bottom .center .item input {display:inline-block;width:227px;height:22px;padding:0;position:absolute;border:0;outline:0;font-size:14px;letter-spacing:0;}
        .login-main .login-bottom .center .item .icon-1 {background:url(../images/icon-login.png) no-repeat 1px 0;}
        .login-main .login-bottom .center .item .icon-2 {background:url(../images/icon-login.png) no-repeat -54px 0;}
        .login-main .login-bottom .center .item .icon-3 {background:url(../images/icon-login.png) no-repeat -106px 0;}
        .login-main .login-bottom .center .item .icon-4 {background:url(../images/icon-login.png) no-repeat 0 -43px;position:absolute;right:-10px;cursor:pointer;}
        .login-main .login-bottom .center .item .icon-5 {background:url(../images/icon-login.png) no-repeat -55px -43px;}
        .login-main .login-bottom .center .item .icon-6 {background:url(../images/icon-login.png) no-repeat 0 -93px;position:absolute;right:-10px;margin-top:8px;cursor:pointer;}
        .login-main .login-bottom .tip .icon-nocheck {display:inline-block;width:10px;height:10px;border-radius:2px;border:solid 1px #9abcda;position:relative;top:2px;margin:1px 8px 1px 1px;cursor:pointer;}
        .login-main .login-bottom .tip .icon-check {margin:0 7px 0 0;width:14px;height:14px;border:none;background:url(../images/icon-login.png) no-repeat -111px -48px;}
        .login-main .login-bottom .center .item .icon {display:inline-block;width:33px;height:22px;}
        .login-main .login-bottom .center .item {width:288px;height:35px;border-bottom:1px solid #dae1e6;margin-bottom:35px;}
        .login-main {width:428px;position:relative;float:left;}
        .login-main .login-top {height:117px;background-color:#148be4;border-radius:12px 12px 0 0;font-family:SourceHanSansCN-Regular;font-size:30px;font-weight:400;font-stretch:normal;letter-spacing:0;color:#fff;line-height:117px;text-align:center;overflow:hidden;-webkit-transform:rotate(0);-moz-transform:rotate(0);-ms-transform:rotate(0);-o-transform:rotate(0);transform:rotate(0);}
        .login-main .login-top .bg1 {display:inline-block;width:74px;height:74px;background:#fff;opacity:.1;border-radius:0 74px 0 0;position:absolute;left:0;top:43px;}
        .login-main .login-top .bg2 {display:inline-block;width:94px;height:94px;background:#fff;opacity:.1;border-radius:50%;position:absolute;right:-16px;top:-16px;}
        .login-main .login-bottom {width:428px;background:#fff;border-radius:0 0 12px 12px;padding-bottom:53px;}
        .login-main .login-bottom .center {width:288px;margin:0 auto;padding-top:40px;padding-bottom:15px;position:relative;}
        .login-main .login-bottom .tip {clear:both;height:16px;line-height:16px;width:288px;margin:0 auto;}
        body {background:url(../images/loginbg.png) 0% 0% / cover no-repeat;position:static;font-size:12px;}
        input::-webkit-input-placeholder {color:#a6aebf;}
        input::-moz-placeholder {/* Mozilla Firefox 19+ */            color:#a6aebf;}
        input:-moz-placeholder {/* Mozilla Firefox 4 to 18 */            color:#a6aebf;}
        input:-ms-input-placeholder {/* Internet Explorer 10-11 */            color:#a6aebf;}
        input:-webkit-autofill {/* 取消Chrome记住密码的背景颜色 */            -webkit-box-shadow:0 0 0 1000px white inset !important;}
        html {height:100%;}
        .login-main .login-bottom .tip {clear:both;height:16px;line-height:16px;width:288px;margin:0 auto;}
        .login-main .login-bottom .tip .login-tip {font-family:MicrosoftYaHei;font-size:12px;font-weight:400;font-stretch:normal;letter-spacing:0;color:#9abcda;cursor:pointer;}
        .login-main .login-bottom .tip .forget-password {font-stretch:normal;letter-spacing:0;color:#1391ff;text-decoration:none;position:absolute;right:62px;}
        .login-main .login-bottom .login-btn {width:288px;height:40px;background-color:#1E9FFF;border-radius:16px;margin:24px auto 0;text-align:center;line-height:40px;color:#fff;font-size:14px;letter-spacing:0;cursor:pointer;border:none;}
        .login-main .login-bottom .center .item .validateImg {position:absolute;right:1px;cursor:pointer;height:36px;border:1px solid #e6e6e6;}
        .footer {left:0;bottom:0;color:#fff;width:100%;position:absolute;text-align:center;line-height:30px;padding-bottom:10px;text-shadow:#000 0.1em 0.1em 0.1em;font-size:14px;}
        .padding-5 {padding:5px !important;}
        .footer a,.footer span {color:#fff;}
        @media screen and (max-width:428px) {.login-main {width:360px !important;}
            .login-main .login-top {width:360px !important;}
            .login-main .login-bottom {width:360px !important;}
        }
    </style>
</head>
<body>
<div class="main-body">
    <div class="login-main">
        <div class="login-top">
            <span>LayuiMini后台登录</span>
            <span class="bg1"></span>
            <span class="bg2"></span>
        </div>
        <form class="layui-form login-bottom" action="/login" method="post">
            <div class="center">
                <div class="item">
                    <span class="icon icon-2"></span>
                    <input type="text" name="uname" lay-verify="required"  placeholder="请输入登录账号" maxlength="24"/>
                </div>

                <div class="item">
                    <span class="icon icon-3"></span>
                    <input type="password" name="pwd" lay-verify="required"  placeholder="请输入密码" maxlength="20">
                    <span class="bind-password icon icon-4"></span>
                </div>

            </div>
            <div class="tip">
                <span class="icon-nocheck"></span>
                <span class="login-tip">保持登录</span>
                <a href="javascript:" class="forget-password">忘记密码？</a>
            </div>
            <div class="layui-form-item" style="text-align:center; width:100%;height:100%;margin:0px;">
                <button class="login-btn" type="submit" lay-submit="" lay-filter="login">立即登录</button>
            </div>
        </form>
    </div>
</div>
<div class="footer">
    ©版权所有 2014-2018 叁贰柒工作室<span class="padding-5">|</span><a target="_blank" href="http://www.miitbeian.gov.cn">粤ICP备16006642号-2</a>
</div>
<script src="../lib/layui-v2.6.3/layui.js" charset="utf-8"></script>
<script>
    //原本想用json的post发送，结果发现后端数据得自己解析，为了降低难度，直接用form表单的post提交，这样后端直接拿数据即可（不然还得解析Json数据）
    // layui.use(['form','jquery'], function () {
    //     var $ = layui.jquery,
    //         form = layui.form,
    //         layer = layui.layer;
    //
    //     // 登录过期的时候，跳出ifram框架
    //     if (top.location != self.location) top.location = self.location;
    //
    //     $('.bind-password').on('click', function () {
    //         if ($(this).hasClass('icon-5')) {
    //             $(this).removeClass('icon-5');
    //             $("input[name='pwd']").attr('type', 'password');
    //         } else {
    //             $(this).addClass('icon-5');
    //             $("input[name='pwd']").attr('type', 'text');
    //         }
    //     });
    //
    //     $('.icon-nocheck').on('click', function () {
    //         if ($(this).hasClass('icon-check')) {
    //             $(this).removeClass('icon-check');
    //         } else {
    //             $(this).addClass('icon-check');
    //         }
    //     });
    //
    //     // 进行登录操作
    //     form.on('submit(login)', function (data) {
    //         data = data.field;
    //         if (data.uname == '') {
    //             layer.msg('用户名不能为空');
    //             return false;
    //         }
    //         if (data.pwd == '') {
    //             layer.msg('密码不能为空');
    //             return false;
    //         }
    //         $.ajax({
    //             url:'/login',
    //             method:'post',
    //             data:data,
    //             dataType:'JSON',
    //             success:function(res){
    //                 if (res.msg==='登录成功'){
    //                     layer.msg('登录成功', function () {
    //                         window.location = '../index.html';
    //                     });
    //                 }else {
    //                     layer.msg("登录失败");
    //                 }
    //             },
    //             error:function (data) {
    //             }
    //         }) ;
    //
    //
    //         return false;
    //     });
    // });
</script>
</body>
</html>

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当然以上代码有一部分注释掉了，原因是如果用JSON格式发送post请求，后端的servlet（准确的说是Tomcat的解析）并没有帮我们解析封装这部分数据，所以我们无法直接get到，得自己另外解析数据，当然也有一些第三方的工具包可以帮我们做这些事情（如阿里的fastjson等），这里为了使其更加简单，所以采用表单提交post请求的方式，这样解析的工作就不用我们做了。

效果是这样的：

如果你没学过layui或者对前端不太行，你也可以这样

一样的功能，不过看上去的效果就不怎么好了。

③编写servlet程序

当有了前端的页面，看上去好了很多，但实质校验的程序我们还没有写。

想象一下我们就是后端程序，当前端的数据历经艰险，从错综复杂的网络中到达我们的服务器，然后经过系统分发到相应端口，这时恰在此端口的tomcat程序接受到了HTTP请求并对其封装，经过一系列骚操作后分发到了我们手中，而我们要做的就是拿着这个封装好的请求进行校验操作，然后对返回对象进行相应修改。而这也是servlet类所需要做的。

package com.dreamchaser.loginTest;

import com.dreamchaser.loginTest.mapper.UserMapper;

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

public class LoginServlet extends HttpServlet {
    static UserMapper userMapper=UserMapper.getUserMapper();

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

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String uname=req.getParameter("uname");
        String pwd=req.getParameter("pwd");
        ServletOutputStream outputStream = resp.getOutputStream();
        String result;
        if (pwd.equals(userMapper.getPwdByName(uname))){
            //响应
            result="登录成功";
        }else {
            result="登录失败";
        }
        outputStream.write(result.getBytes());
    }
}


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你可能会疑惑这个UserMapper是什么，别急，后面会介绍。

④封装jdbc操作，编写简单的数据库连接池

在操作数据库之前，最好写个简单的数据库连接池。一个是简化我们的操作，一个是节省开销，提高性能（Connection是个非常耗费资源的对象，频繁的创建和回收将会是一笔巨大的开销）