前端JavaScript验证后正确调用Java Servlet的策略与实践

<script>
    const formSubmit = document.getElementById("formSubmit");
    const loginForm = document.querySelector(".loginForm"); // 获取表单元素

    formSubmit.addEventListener("click", (e) => {
        const Rno = document.getElementById("Rno").value;
        const Password = document.getElementById("pass").value;

        // 客户端验证逻辑
        if (Rno === null || Rno === "" || Password.length < 7) {
            alert("请输入房间号或密码不正确（至少7位）");
            // 只有当验证失败时才阻止表单的默认提交行为
            e.preventDefault(); 
            // 可以在这里选择是否重新加载页面，但通常不建议在验证失败时自动刷新
            // setTimeout(function () {
            //     window.location.reload();
            // }, 5000);
        }
        // 如果验证通过，则不调用 e.preventDefault()，允许表单自然提交
        // 表单的 method="post" 和 action="LoginServlet" 将会生效
    });

    // 更好的做法是监听表单的submit事件，而不是按钮的click事件
    // loginForm.addEventListener("submit", (e) => {
    //     const Rno = document.getElementById("Rno").value;
    //     const Password = document.getElementById("pass").value;
    //     if (Rno === null || Rno === "" || Password.length < 7) {
    //         alert("请输入房间号或密码不正确（至少7位）");
    //         e.preventDefault(); // 阻止表单提交
    //     }
    // });
</script>

import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    public LoginServlet() {
        super();
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8"); // 设置响应内容类型和字符编码
        PrintWriter out = response.getWriter();
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/student","root","root");

            // 获取表单参数
            int roomNo = Integer.parseInt(request.getParameter("Roomno"));
            String password = request.getParameter("password");

            PreparedStatement ps = con.prepareStatement("select * from login where roomNo=? and password=?");
            ps.setInt(1, roomNo);
            ps.setString(2, password);
            ResultSet rs =  ps.executeQuery();

            if(rs.next()) {
                int userRoom = rs.getInt(1);
                String userName = rs.getString(3);
                out.println("RoomNo:"+userRoom+" is allocated to "+ userName);
                // 登录成功后，通常会进行页面重定向或设置会话信息
                // response.sendRedirect("welcome.jsp"); 
            } else {
                out.println("Failed to log in");
                // 登录失败，可以重定向回登录页并显示错误信息
                // request.setAttribute("errorMessage", "用户名或密码错误");
                // request.getRequestDispatcher("Login.jsp").forward(request, response);
            }
            con.close();

        } catch (ClassNotFoundException e) {
            out.println("数据库驱动加载失败: " + e.getMessage());
            e.printStackTrace();
        } catch (SQLException e) {
            out.println("数据库操作失败: " + e.getMessage());
            e.printStackTrace();
        } catch (NumberFormatException e) {
            out.println("房间号格式不正确: " + e.getMessage());
            e.printStackTrace();
        } finally {
            out.close(); // 确保PrintWriter关闭
        }
    }

    // 如果需要处理GET请求，则实现doGet方法
    // protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //     // 例如，直接转发到登录页面
    //     request.getRequestDispatcher("Login.jsp").forward(request, response);
    // }
}