昨天那个小测试我们完成了注册界面，今天我们来完成一下登陆界面：

首先上结果图：

Servlet代码：

1：首先我们需要继承HttpServlet类，然后重写方法：doGet和doPost

2：然后就是常规的一开始的编码设置：

req.setCharacterEncoding("UTF-8");

3：接下来我们定义两个String字符串用来接受前端传过来的值（也就是用户输入以后提交的）

String name = req.getParameter("username");
        String passwd = req.getParameter("passWd");

4：接下来就是基本的JDBC操作：

String url = "jdbc:mysql://localhost:3306/servletstudy";
   Class.forName("com.mysql.cj.jdbc.Driver");
   Connection comm = DriverManager.getConnection(url,"root","root");

由于这里是要查询，所以我们定义SQL语句这样写：

String SQL = "SELECT * FROM user where(username=? and password =?)";

预编译sql，然后执行：

PreparedStatement pstmt = comm.prepareStatement(SQL);
                pstmt.setString(1,name);
                pstmt.setString(2,passwd);
                ResultSet rs = pstmt.executeQuery();

然后就是使用一个循环与数据库里面的对象作比较：

if(rs.next()){.....}

在判断语句里面写重定向：

if(rs.next()){
                    if(rs!=null){
                        rs.close();
                    }
                    if(pstmt!=null){
                        pstmt.close();
                    }
                    if(comm!=null){
                        comm.close();
                    }
// dis = req.getRequestDispatcher("http://localhost:8080/javaWeb_war_exploded/hello.jsp");
// dis.forward(req,resp);
                    resp.sendRedirect("http://localhost:8080/hello.jsp");
                    System.out.println("hah");
                }else{
                    if(rs!=null){
                        rs.close();
                    }
                    if(pstmt!=null){
                        pstmt.close();
                    }
                    if(comm!=null){
                        comm.close();
                    }
// dis = req.getRequestDispatcher("http://localhost:8080/javaWeb_war_exploded/fruit.jsp");
// dis.forward(req,resp);
                    resp.sendRedirect("http://localhost:8080/false.jsp");
                }

全部Loginservlet代码：

package com.ftz.Demo.Servlet;

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.sql.*;

/** * @author ${范涛之} * @Description * @create 2021-12-07 4:32 */
public class Login extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.doGet(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        req.setCharacterEncoding("UTF-8");
        String name = req.getParameter("username");
        String passwd = req.getParameter("passWd");
        RequestDispatcher dis =null;
        System.out.println(name+passwd);
        try {
            try {
                String url = "jdbc:mysql://localhost:3306/servletstudy";
                Class.forName("com.mysql.cj.jdbc.Driver");
                Connection comm = DriverManager.getConnection(url,"root","root");
                String SQL = "SELECT * FROM user where(username=? and password =?)";
                //结果集
                PreparedStatement pstmt = comm.prepareStatement(SQL);
                pstmt.setString(1,name);
                pstmt.setString(2,passwd);
                ResultSet rs = pstmt.executeQuery();
// System.out.println(rs.getString(1));
// System.out.println(rs.getString(2));
// System.out.println(rs.getString(3));
                if(rs.next()){
                    if(rs!=null){
                        rs.close();
                    }
                    if(pstmt!=null){
                        pstmt.close();
                    }
                    if(comm!=null){
                        comm.close();
                    }
// dis = req.getRequestDispatcher("http://localhost:8080/javaWeb_war_exploded/hello.jsp");
// dis.forward(req,resp);
                    resp.sendRedirect("http://localhost:8080/hello.jsp");
                    System.out.println("hah");
                }else{
                    if(rs!=null){
                        rs.close();
                    }
                    if(pstmt!=null){
                        pstmt.close();
                    }
                    if(comm!=null){
                        comm.close();
                    }
// dis = req.getRequestDispatcher("http://localhost:8080/javaWeb_war_exploded/fruit.jsp");
// dis.forward(req,resp);
                    resp.sendRedirect("http://localhost:8080/false.jsp");
                }

            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}
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