在网页上执行SQL命令后创建警告框

Question

try
        {  
            int num=0;
            String user=request.getParameter("username");
            String password=request.getParameter("password");
            String query="select * from registeredUsers where (userid=? or emailid=?) and (password=?)";
            Class.forName("com.mysql.jdbc.Driver");
            Connection con=DriverManager.getConnection("jdbc:mysql:///kush_cabs","root","");
            PreparedStatement pst=con.prepareStatement(query);
            pst.setString(1,user);
            pst.setString(2,user);
            pst.setString(3,password);
            ResultSet rs=pst.executeQuery();
            if(rs.next())
                num=rs.getRow();
            if(num>=1)
            {
                String name=rs.getString(2);
                h1.setAttribute("username",name);
                h1.setAttribute("userid",user);
                response.sendRedirect("UserMain.jsp");
            }
            else
            {
                out.println("<script='text/javascript'>");
                out.println("alert('please enter the valid username');");
                out.println("</script>");
            }
        }
        catch(Exception ae)
        {
            out.println(ae.getMessage());
        }

不显示警告框。该消息显示在"alert('请输入有效用户名');"

Answer 1

您缺少type属性。使用out.println("<script type='text/javascript'>");