使用Servlet完成用户登录

本文我们将创建一个简单的用户登录示例，本文使用MySQL5.7作为数据库。

1 创建表和准备数据

在MySQL的test数据库中创建t_user表：

CREATE TABLE `t_user` (
   `id` int(11) NOT NULL AUTO_INCREMENT,
   `username` varchar(50) DEFAULT NULL,
   `password` varchar(50) DEFAULT NULL,
   PRIMARY KEY (`id`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8

插入一些测试数据，待会登录使用：

2 编写登录页面

编写login.jsp，用于用户登录：

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>一点教程网-使用Servlet完成用户登录</title>
</head>
<body>
<h1>使用Servlet完成用户登录</h1>
<form action="Login" method="post">
    用户名:<input type="text" name="username"/><br/><br/>
    密码:<input type="password" name="userpass"/><br/><br/>
    <input type="submit" value="登录"/>
</form>
</body>
</html>

3 编写LoginServlet

LoginServlet用于查询数据库用户表，以完成用户身份校验逻辑：

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;

/**
 * 一点教程网 - http://www.yiidian.com
 */
public class LoginServlet extends HttpServlet {

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();

        String n=request.getParameter("username");
        String p=request.getParameter("userpass");

        if(LoginDao.validate(n, p)){
            RequestDispatcher rd=request.getRequestDispatcher("Welcome");
            rd.forward(request,response);
        }
        else{
            out.print("抱歉，用户名或密码错误");
            RequestDispatcher rd=request.getRequestDispatcher("login.jsp");
            rd.include(request,response);
        }

        out.close();
    }

}

4 编写LoginDao

LoginDao用于处理数据库查询的具体逻辑：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

/**
 * 一点教程网 - http://www.yiidian.com
 */
public class LoginDao {

    public static boolean validate(String name,String pass){
        boolean status=false;
        try{
            Class.forName("com.mysql.jdbc.Driver");
            Connection con= DriverManager.getConnection(
                    "jdbc:mysql://localhost:3306/test","root","root");

            PreparedStatement ps=con.prepareStatement(
                    "select * from t_user where username=? and password=?");
            ps.setString(1,name);
            ps.setString(2,pass);

            ResultSet rs=ps.executeQuery();
            status=rs.next();

        }catch(Exception e){
            System.out.println(e);
        }
        return status;
    }
}

5 编写WelcomeServlet

WelcomeServlet是登录成功后的用户欢迎页面：

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

/**
 * 一点教程网 - http://www.yiidian.com
 */
public class WelcomeServlet extends HttpServlet {

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();

        String n=request.getParameter("username");
        out.print("欢迎你 "+n);

        out.close();
    }

}

6 配置web.xml

<?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_3_1.xsd"
         version="3.1">

    <servlet>
        <servlet-name>LoginServlet</servlet-name>
        <servlet-class>LoginServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/Login</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>WelcomeServlet</servlet-name>
        <servlet-class>WelcomeServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>WelcomeServlet</servlet-name>
        <url-pattern>/Welcome</url-pattern>
    </servlet-mapping>

</web-app>