.net 开发中对ASHX文件用处的疑问

我对.NET开发的经验还稍浅,以前是开发JAVA的.可能由于能力问题现在对很多基础概念理解不深。处于能开发，但是不能有效率高质量的开发。对于ashx文件我们技术总监给我的建议，也是浅显易懂。大部分的时候用来处理ajax的程序代码。但是我深深受那种action的思想，总觉得它这个类和java的action类似乎能做一样的事情，于是就把它写成了这个样子。业务逻辑，页面跳转都能正常的跳转。也能正常的登录和注销。总而言之这样子是能跑的起来的。
但是我想知道我这样写代码的弊端在哪里。或者说有致命的问题，那么我肯定就要把它改正了。
然而我们这个项目 有很多模块都需要登录，有点整合的意味。所以我一定要把表单处理给通用化。
不能写在页面的cs类里面、

//我前台是依靠 UserAction.ashx?Method=UserNameLogin 这样的action值把参数提交过来的
然后调用业务逻辑层做操作，最终返回结果跳转页面。

<%@ WebHandler Language="C#" Class="UserAction" %>



using System;

using System.Web;

using System.Web.SessionState;



public class UserAction : IHttpHandler,IRequiresSessionState{



    private HttpContext Mcontext;

    private string FromUrl;

    

    public void ProcessRequest(HttpContext context) {



        context.Response.ContentType = "text/html;charset=utf-8"; ;

        Mcontext = context;

        string Method = context.Request["Method"];

        FromUrl = context.Request.ServerVariables["HTTP_REFERER"];//保存从何页面发送来的请求,权限不通过则返回

        

        switch (Method)

        {

            case "UserNameLogin" : UserNameLogin(); break;

            case "UserPhoneLogin": UserPhoneLogin(); break;

            case "UserExit": UserExit(); break;

        }

        

    }



    public void UserExit() //退出用户

    {

        Mcontext.Session["User"] = null;

        Mcontext.Session["BUser"] = null;

        Mcontext.Response.Write("<script> alert('退出成功！');</script>");

        Mcontext.Response.Write("<script> location.href='index.aspx'; </script>");

    }



    public void UserPhoneLogin()//根据手机号登录

    {

        string UserType = "";

        string UserName = "";

        string UserPassword = "";

        UserType = Mcontext.Request["usertype"];

        UserName = Mcontext.Request["username"];

        UserPassword = Mcontext.Request["password"];



        if (UserType == "1")//个人登录

        {

            FYM_User fu = new FYM_User();

            fu.U_phone = UserName;

            fu.U_password = UserPassword;

            UserBLL ub = new UserBLL();



            fu = ub.LoginByUpPwd(fu);



            if (fu.id != 0)

            {

                Mcontext.Session["User"] = fu;

                Mcontext.Session["BUser"] = null;



                Mcontext.Response.Write("<script> alert('登录成功！欢迎您:" + fu.U_username + "您的用户类别为个人用户');</script>");

                Mcontext.Response.Write("<script> location.href='index.aspx'; </script>");

            }

            else

            {

                Mcontext.Response.Write("<script> alert('登录失败,个人手机号或密码错误！');</script>");

                Mcontext.Response.Write("<script> location.href='" + FromUrl + "'; </script>");

            }





        }



        if (UserType == "2")//企业登录

        {

            FYM_BusinessUser fu = new FYM_BusinessUser();

            fu.B_userphone = UserName;

            fu.B_password = UserPassword;

            BUserBLL ub = new BUserBLL();



            fu = ub.LoginByUpPwd(fu);



            if (fu.id != 0)

            {

                Mcontext.Session["User"] = null;

                Mcontext.Session["BUser"] = fu;



                Mcontext.Response.Write("<script> alert('登录成功！欢迎您:" + fu.B_username + "您的用户类别为企业用户');</script>");

                Mcontext.Response.Write("<script> location.href='index.aspx'; </script>");

            }

            else

            {

                Mcontext.Response.Write("<script> alert('登录失败,企业联系人电话或密码错误！');</script>");

                Mcontext.Response.Write("<script> location.href='" + FromUrl + "'; </script>");

            }

        }

    }



    public void UserNameLogin() //根据用户名登录

    {

        string UserType = "";

        string UserName = "";

        string UserPassword = "";

        UserType = Mcontext.Request["usertype"];

        UserName = Mcontext.Request["username"];

        UserPassword = Mcontext.Request["password"];



        if (UserType == "1")//个人登录

        {

            FYM_User fu = new FYM_User();

            fu.U_username = UserName;

            fu.U_password = UserPassword;

            UserBLL ub = new UserBLL();



            fu = ub.LoginByUnPwd(fu);



            if (fu.id != 0)

            {

                Mcontext.Session["User"] = fu;

                Mcontext.Session["BUser"] = null;

                

                Mcontext.Response.Write("<script> alert('登录成功！欢迎您:"+fu.U_username+"您的用户类别为个人用户');</script>");

                Mcontext.Response.Write("<script> location.href='index.aspx'; </script>");

            }

            else 

            {

                Mcontext.Response.Write("<script> alert('登录失败,个人用户名或密码错误！');</script>");

                Mcontext.Response.Write("<script> location.href='" + FromUrl + "'; </script>");

            }

        

            

        }



        if (UserType == "2")//企业登录

        {

            FYM_BusinessUser fu = new FYM_BusinessUser();

            fu.B_username = UserName;

            fu.B_password = UserPassword;

            BUserBLL ub = new BUserBLL();



            fu = ub.LoginByUnPwd(fu);



            if (fu.id != 0)

            {

                Mcontext.Session["User"] = null;

                Mcontext.Session["BUser"] = fu;



                Mcontext.Response.Write("<script> alert('登录成功！欢迎您:" + fu.B_username + "您的用户类别为企业用户');</script>");

                Mcontext.Response.Write("<script> location.href='index.aspx'; </script>");

            }

            else

            {

                Mcontext.Response.Write("<script> alert('登录失败,企业用户名或密码错误！');</script>");

                Mcontext.Response.Write("<script> location.href='" + FromUrl + "'; </script>");

            }

        }

        

    }

    

    

    

    public bool IsReusable {

        get {

            return false;

        }

    }



}