jsp验证登陆代码

<form action="loginServlet" method="post">
    用户名: <input type="text" name="username"><br>
    密码: <input type="password" name="password"><br>
    <input type="submit" value="登录">
</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");

        // 数据库连接信息
        String url = "jdbc:mysql://localhost:3306/mydatabase";
        String dbUsername = "root";
        String dbPassword = "password";

        try {
            Connection conn = DriverManager.getConnection(url, dbUsername, dbPassword);
            String sql = "SELECT * FROM users WHERE username=? AND password=?";
            PreparedStatement pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, username);
            pstmt.setString(2, password);
            ResultSet rs = pstmt.executeQuery();

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

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