登录项目

步骤

1.首先写一个前台页面，一个form表单——login.jsp


<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    <center>
        <h1><%=request.getAttribute("msg")==null?"":request.getAttribute("msg")%></h1>
        <h1>登录界面</h1>
        <form action="/MyServlet20230624_war_exploded/login">
            用户名：
            <input type="text" name="username" placeholder="请输入用户名">
            <br>
            密码：
            <input type="password" name="password" placeholder="请输入密码">
            <br>
            <input type="submit" value="登录">

        </form>
    </center>

</body>
</html>

效果图：

2.后台获取前台输入的参数，并作校验

  request.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");
        String username = request.getParameter("username").trim();
        String password = request.getParameter("password").trim();
        if(username.isEmpty()||username==""||password.isEmpty()||password==""){
            response.getWriter().write("<h1 style='color:red'>用户名或密码为空</h1>");
            return;
        }

3.写一个JDBC工具类，用来连接数据库，本案例使用Druid连接池

package org.xingyun.utils;

import com.alibaba.druid.pool.DruidDataSourceFactory;

import javax.sql.DataSource;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;

public class JDBCUtils {
    public static DataSource getDataSource() throws Exception {
        Properties properties = new Properties();
        InputStream in = JDBCUtils.class.getClassLoader().getResourceAsStream("druid.properties");
        properties.load(in);
        DataSource ds = DruidDataSourceFactory.createDataSource(properties);
        return ds;
    }

    public static void close(Connection conn, Statement stmt, ResultSet rs) throws SQLException {
        if (conn != null) {
            conn.close();
        }

        if (stmt != null) {
            stmt.close();
        }

        if (rs != null) {
            rs.close();
        }
    }
}

4.写一个登录工具类，在数据库中查询数据，再把数据对象返回到主类中

package org.xingyun.utils;

import beans.User;

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

public class LoginServer {
    public static User getLogin(String username,String password) throws Exception {
        User user;
        Connection conn = JDBCUtils.getDataSource().getConnection();
        String sql="select * from user where username=? and password=?";
        PreparedStatement preparedStatement = conn.prepareStatement(sql);
        preparedStatement.setString(1,username);
        preparedStatement.setString(2,password);
        ResultSet rs = preparedStatement.executeQuery();
        if (rs.next()==false) {
            user=null;
        } else {
            int id = rs.getInt(1);
            String uname = rs.getString(2);
            String pwd = rs.getString(3);
            User userer = new User(id,uname,pwd);
            user=userer;
        }
        JDBCUtils.close(conn,preparedStatement,rs);
        return user;

    }
}

5.在主类中判断是否能登录成功，成功则跳转页面

package org.xingyun.demo3;

import beans.User;
import org.xingyun.utils.LoginServer;

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 java.io.IOException;

@WebServlet(name = "LoginServlet",value = "/login")
public class LoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");
        String username = request.getParameter("username").trim();
        String password = request.getParameter("password").trim();
        if(username.isEmpty()||username==""||password.isEmpty()||password==""){
            response.getWriter().write("<h1 style='color:red'>用户名或密码为空</h1>");
            return;
        }

        try {
            User user = LoginServer.getLogin(username, password);
            if (user != null) {
                request.setAttribute("username", user.getUsername()+"已登录");
                request.getRequestDispatcher("/main.jsp").forward(request, response);
            } else {
                request.setAttribute("msg","登录失败，请重新输入");
                request.getRequestDispatcher("/login.jsp").forward(request,response);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }


    }

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

注册项目

package org.xingyun.demo3;

import beans.User;
import org.xingyun.utils.JDBCUtils;
import org.xingyun.utils.LoginServer;
import org.xingyun.utils.RegisterServer;

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 java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;

@WebServlet(name = "LoginServlet",value = "/login")
public class LoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");
        String username = request.getParameter("username").trim();
        String password = request.getParameter("password").trim();
        if(username.isEmpty()||username==""||password.isEmpty()||password==""){
            response.getWriter().write("<h1 style='color:red'>用户名或密码为空</h1>");
            return;
        }


        try {
            boolean flag = RegisterServer.getRegister(username, password);
            if (flag == false) {
                Connection conn = JDBCUtils.getDataSource().getConnection();
                String sql = "insert into user(username,password) values (?,?)";
                PreparedStatement preparedStatement = conn.prepareStatement(sql);
                preparedStatement.setString(1, username);
                preparedStatement.setString(2, password);
                int i = preparedStatement.executeUpdate();
                if (i > 0) {
                    request.setAttribute("msg", "注册成功");
                    request.getRequestDispatcher("/login.jsp").forward(request,response);
                }
            } else {
                request.setAttribute("msg", "该用户名已注册，请重新注册");
                request.getRequestDispatcher("/login.jsp").forward(request,response);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }


//  登录操作
//        try {
//            User user = LoginServer.getLogin(username, password);
//            if (user != null) {
//                request.setAttribute("username", user.getUsername()+"已登录");
//                request.getRequestDispatcher("/main.jsp").forward(request, response);
//            } else {
//                request.setAttribute("msg","登录失败，请重新输入");
//                request.getRequestDispatcher("/login.jsp").forward(request,response);
//            }
//        } catch (Exception e) {
//            e.printStackTrace();
//        }


    }

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

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