selves

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.*;

@WebServlet("/Login")
public class LoginServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req,resp);//转发到get 执行相同逻辑
    }

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

        //获取参数
        String name = req.getParameter("username");
        String password = req.getParameter("pwd");


        String error = null; //错误信息
        boolean flag = false; //是否登陆成功
        //验证数据可靠性
        if(name == null || password == null || name.equals("") || password.equals("")){
            error="用户名和密码不能为空!";
        }else {
            //查询数据库
            try {
                Class.forName("com.mysql.jdbc.Driver");
                Connection connect = DriverManager.getConnection("jdbc:mysql://127.0.0.1/db1?charsetEncoding=utf-8&user=root&password=admin");
                PreparedStatement statement = connect.prepareStatement("select *from user where name = ? and password = ?");
                statement.setObject(1,name);
                statement.setObject(2,password);
                ResultSet set = statement.executeQuery();
                if(set.next()){
                    flag = true;
                }else{
                    error="用户名和密码错误!";
                }
            } catch (ClassNotFoundException | SQLException e1) {
                error = "服务器忙,请稍后再试!";
            }
        }

        if(flag){
            //删除已存在的错误信息,避免后续登录页面展示重复展示
            req.getSession().removeAttribute("error");
            //添加用户名称到session
            req.getSession().setAttribute("user",name);
            //跳转页面
            req.getRequestDispatcher("./index.jsp").forward(req,resp);
        }else{
            //添加错误信息到session
            req.getSession().setAttribute("error",error);
            //跳转页面
            req.getRequestDispatcher("./login.jsp").forward(req,resp);
        }
    }
}