第一步：配置环境

（如果已经配置完成请省略，这一步直接代码复制就好）

在pom.xml引入servlet等依赖

    <dependencies>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <scope>provided</scope>
        </dependency>
        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.49</version>
        </dependency>

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.15.0</version>
        </dependency>
    </dependencies>

在src目录下创建webapp/WEB-INF/web.xml

这段代码赋值粘贴进web.xml

<!DOCTYPE web-app PUBLIC
        "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
        "http://java.sun.com/dtd/web-app_2_3.dtd" >
<web-app>
    <display-name>Archetype Created Web Application</display-name>
</web-app>

第二步：编写前端html的form表单

在webapp目录下，创建一个html，注意是webapp下，不是WEB-INF下

html代码（复制这个）

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <form action="login" method="post">
        <input type="text" name="username">
        <input type="text" name="password">
        <input type="submit" value="提交">
    </form>
</body>
</html>

如果正确的话，结果如下

解释

第三步：编写登录的java

在main/java中创建两个java文件，分别来管理登录和跳转的页面

loginservlet代码（复制这个）

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 javax.servlet.http.HttpSession;
import java.io.IOException;

@WebServlet("/login")
public class loginservlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf8");
        resp.setContentType("text/html;charset=utf8");
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        HttpSession session = req.getSession(true);
        session.setAttribute("username",username);
        session.setAttribute("password",password);
        resp.sendRedirect("index");
    }
}

解释

indexservlet代码（复制这个）

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 javax.servlet.http.HttpSession;
import java.io.IOException;

@WebServlet("/index")
public class indexservlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        HttpSession session = req.getSession(false);
        req.setCharacterEncoding("utf8");
        resp.setContentType("text/html;charset=utf8");
        String username = (String)session.getAttribute("username");
        String password = (String)session.getAttribute("password");
        resp.getWriter().write("您的姓名是"+username+"您的密码是"+password);
    }
}