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);     // } }