jsp模拟登录

<form action="loginServlet" method="post">
    Username: <input type="text" name="username"><br>
    Password: <input type="password" name="password"><br>
    <input type="submit" value="Login">
</form>

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;

public class LoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");

        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydb", "user", "password");
            PreparedStatement ps = conn.prepareStatement("SELECT * FROM users WHERE username=? AND password=?");
            ps.setString(1, username);
            ps.setString(2, password);
            ResultSet rs = ps.executeQuery();

            if (rs.next()) {
                HttpSession session = request.getSession();
                session.setAttribute("username", username);
                response.sendRedirect("welcome.jsp");
            } else {
                response.sendRedirect("login.jsp?error=1");
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

<%
    HttpSession session = request.getSession(false);
    if (session != null && session.getAttribute("username") != null) {
        String username = (String) session.getAttribute("username");
%>
        Welcome, <%= username %>!
<%
    } else {
        response.sendRedirect("login.jsp");
    }
%>