java当重定向回另一个servlet时，如何显示错误消息？

3 月，1 周 Questions & Answers 181

我有一个名为LoginPage的java servlet，它是用户将登录信息输入表单的可视化界面，还有一个名为login的servlet，它是一个临时页面，只是在重定向到另一个servlet之前检查、查询数据库以确认它确实是一个有效的登录

//LoginPage
try (PrintWriter out = response.getWriter()) {
            out.println("<!DOCTYPE html>");
            out.println("<html>");
            out.println("<head>");
            out.println("<title>Login</title>");        
            out.println("</head>");
            out.println("<body>");
            out.println("<h1>Activities Week Login</h1></br>");
            out.println("<form action=\"login\" method=\"post\">"
                    + "Email:</br>"
                    + "<input type='text' name='Email'></br>"
                    +"Password:</br>"
                    + "<input type='password' name='Password'></br></br>"
                    + "<input type='submit' value='Submit'></form>");
            out.println("</br></br></br>");
            out.println("Dont have an account yet? <a href=\'createaccountpage\'>Create one.</a></br></br>");
            out.println("Forgotten your password? <a href=\'forgottenpasswordpage\'>Reset it.</a>");
            out.println("</body>");
            out.println("</html>");
        }

//Login
SQLConnection sqlconnection = new SQLConnection();
        String Email = (String)request.getParameter("Email");
        String Password = (String)request.getParameter("Password");


        if(sqlconnection.checkValidLogin(Email, Password) == false)//If the login details are incorrect:
        {
            PrintWriter out = response.getWriter();
            out.println("<meta http-equiv='refresh' content='3;URL='>");//redirects after 3 seconds
            out.println("<p style='color:red;'>Login unsuccessful! Please check your details and try again.</p>");      
            response.sendRedirect("");
        }
        else//If the login details are correct:
        {
            User currentUser = sqlconnection.getCurrentUser(Email);
            HttpSession session = request.getSession();
            session.setAttribute("Email", Email);

            if(sqlconnection.isUserTeacher(Email)==true)//If the user is a teacher
            {
                Teacher currentTeacher = new Teacher();
                currentTeacher.setUser(currentUser);
                session.setAttribute("currentTeacher", currentTeacher);
                PrintWriter out = response.getWriter();
                out.println("<meta http-equiv='refresh' content='3;URL=studenthomepage'>");//redirects after 3 seconds
                out.println("<p style='color:green;'>Login successful!</p>");
                response.sendRedirect("studenthome");
            }
            else{
                Student currentStudent;
                currentStudent = sqlconnection.getCurrentStudent(Email, currentUser);
                session.setAttribute("currentStudent", currentStudent);
                PrintWriter out = response.getWriter();
                out.println("<meta http-equiv='refresh' content='3;URL=studenthomepage'>");//redirects after 3 seconds
                out.println("<p style='color:green;'>Login successful!</p>");
                response.sendRedirect("studenthome");
            }
        }

在提供的登录信息不正确的情况下，如何显示重定向回LoginPage时保留的错误消息

我已经看到并尝试了一些其他方法（没有帮助），例如登录servlet中已有的方法：

out.println("<meta http-equiv='refresh' content='3;URL=studenthomepage'>");//redirects after 3 seconds
                out.println("<p style='color:green;'>Login successful!</p>");

这种方法不是一个好的解决方案（或者我只是做错了），如果是这样，我应该用什么

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java当重定向回另一个servlet时，如何显示错误消息？

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