每当别人问我关于三层的知识的时候我总是推荐自己的《三层架构之抽象工厂加反射》这篇博客。这篇博客是自己当时学习三层的时候写的一个简单的登录例子。这个例子通过登录这个用例简单的介绍了三层，然后过度的三层+简单工厂再过渡到三层+抽象工厂。不管说从方法命名或者代码风格上来说自己都不敢说是最好的，但是体现三层我感觉还是绰绰有余的。然而最近在给别人讲述三层时候被他人指出这篇博客的代码有些许错误，虽然别人指出的方式有些令自己不快，甚至气愤！但是毕竟还有人关注自己，还有人看自己的博客，还有人给自己指出不足，从这个方面来看这还应该算是好事。有错误就改！有错误才能进步嘛。也许这就是米老师总是说的教学相长吧，这次终于体会到了，而且体会很深刻！！！


教学相长

虽有嘉肴，弗食不知其旨也；虽有至道，弗学不知其善也。是故学然后知不足，教然后知困。知不足，然后能自反也；知困，然后自强也。故曰：教学相长也。

----摘自《礼记•学记》


真的是“知不足”了，真的是想“自强”了，为了验证代码的正确性决定将这个登录的小例子又从最简单的三层开始做起逐步增加难度（降低耦合度），重新实现了一遍。再一次用了用VB.NET，再次回到了傻瓜式的VS环境中。

代码如下：

 简单三层

界面层

Public Class Login
    Private Sub btnLogin_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnLogin.Click
        Dim LUser As New Entity.User
        Dim BCheck As New Bll.BllLogin
        LUser.User_Id = txtUserId.Text
        LUser.User_Pwd = txtPwd.Text
        If BCheck.Check(LUser) = True Then
            MsgBox("登录成功！")
        Else
            MsgBox("登录失败！")
        End If
    End Sub
    Private Sub btnCancle_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCancle.Click
        End
    End Sub
End Class


BLL层

Public Class BllLogin
    Function Check(ByVal User As Entity.User) As Boolean
        Dim DaUser As New DAL.DalUserInfo
        Dim BlUser As New Entity.User
        BlUser.User_Id = User.User_Id
        BlUser = DaUser.Check(BlUser)
        If BlUser.User_Pwd = User.User_Pwd Then
            Return True
        Else
            Return False
        End If
    End Function
End Class


DAL层

Imports System.Data.SqlClient
Public Class DalUserInfo
    Dim ConnStr As String = "Data Source=192.168.24.186;Initial Catalog=Student;User ID=sa;Pwd=123456"
    Dim conn As SqlConnection = New SqlConnection(ConnStr)
    Function Check(ByVal User As Entity.User) As Entity.User
        Dim sql As String = "select * from UserInfo where User_ID='" & User.User_Id + "'"
        Dim cmd As SqlCommand = New SqlCommand(sql, conn)
        Dim read As SqlDataReader
        Try
            conn.Open()
            read = cmd.ExecuteReader
            read.Read()
            User.User_Id = read.Item("User_ID")
            User.User_Pwd = read.Item("User_Pwd")
            Return User
        Catch ex As Exception
            User.User_Pwd = ""
            Return User
        End Try
    End Function
End Class


实体层

Public Class User
    Private userId As String
    Private userPwd As String
    Public Property User_Id() As String
        Get
            Return userId
        End Get
        Set(ByVal value As String)
            userId = value
        End Set
    End Property
    Public Property User_Pwd() As String
        Get
            Return userPwd
        End Get
        Set(ByVal value As String)
            userPwd = value
        End Set
    End Property
End Class


三层+简单工厂

界面层代码不变

Bll层

Public Class BllLogin
    Function Check(ByVal User As Entity.User) As Boolean
        Dim DalFactory As New DAL.DFactory
        Dim BlUser As New Entity.User
        BlUser.User_Id = User.User_Id
        BlUser = DalFactory.CreateUserInfo.Check(BlUser)
        If BlUser.User_Pwd = User.User_Pwd Then
            Return True
        Else
            Return False
        End If
    End Function
End Class


工厂

Imports [Interface]
Public Class DFactory
    'Dim DataBase As String = "Access"
    Dim DataBase As String = "Sql"
    Function CreateUserInfo() As IUserInfo
        Dim DB As IUserInfo
        Select Case DataBase
            Case "Sql"
                DB = New DalUserInfo
                'Case "Access"
                ' DB = New D_UserInfoAccess
        End Select
        Return DB
    End Function
End Class


接口

Public Interface IUserInfo
    Function Check(ByVal IUser As Entity.User) As Entity.User
End Interface


DAL层

Imports System.Data.SqlClient
Public Class DalUserInfo : Implements [Interface].IUserInfo
    Dim ConnStr As String = "Data Source=192.168.24.186;Initial Catalog=Student;User ID=sa;Pwd=123456"
    Dim conn As SqlConnection = New SqlConnection(ConnStr)
    Public Function Check(ByVal IUser As Entity.User) As Entity.User Implements [Interface].IUserInfo.Check
        Dim sql As String = "select * from UserInfo where User_ID='" & IUser.User_Id + "'"
        Dim cmd As SqlCommand = New SqlCommand(sql, conn)
        Dim read As SqlDataReader
        Try
            conn.Open()
            read = cmd.ExecuteReader
            read.Read()
            IUser.User_Id = read.Item("User_ID")
            IUser.User_Pwd = read.Item("User_Pwd")
            Return IUser
        Catch ex As Exception
            IUser.User_Pwd = ""
            Return IUser
        End Try
    End Function
End Class


三层+抽象工厂

界面层代码不变

Bll层代码不变

接口代码不变

工厂代码

Imports [Interface]
Imports System.Reflection
Public Class DFactory
    'Dim DataBase As String = "Access"
    'Dim DataBase As String = "Sql"
    Dim strDB As String = System.Configuration.ConfigurationSettings.AppSettings("DBString")
    Function CreateUserInfo() As IUserInfo
        Return CType(Assembly.Load("DAL").CreateInstance("DAL.DalUserInfo" & strDB), IUserInfo)
    End Function
End Class


DAL层

Imports System.Data.SqlClient
Public Class DalUserInfoSql : Implements [Interface].IUserInfo
    'Dim ConnStr As String = "Data Source=192.168.24.186;Initial Catalog=Student;User ID=sa;Pwd=123456"
    Dim strConnStr As String = System.Configuration.ConfigurationSettings.AppSettings("ConnStr")
    Dim conn As SqlConnection = New SqlConnection(strConnStr)
    Public Function Check(ByVal IUser As Entity.User) As Entity.User Implements [Interface].IUserInfo.Check
        Dim sql As String = "select * from UserInfo where User_ID='" & IUser.User_Id + "'"
        Dim cmd As SqlCommand = New SqlCommand(sql, conn)
        Dim read As SqlDataReader
        Try
            conn.Open()
            read = cmd.ExecuteReader
            read.Read()
            IUser.User_Id = read.Item("User_ID")
            IUser.User_Pwd = read.Item("User_Pwd")
            Return IUser
        Catch ex As Exception
            IUser.User_Pwd = ""
            Return IUser
        End Try
    End Function
End Class


配置文件

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0,Profile=Client" />
  </startup>
  <appSettings>
    <add key="ConnStr" value ="Data Source=192.168.24.186;Initial Catalog=Student;User ID=sa;Pwd=123456"></add>
    <add key="DBString" value ="Sql"></add>
  </appSettings>
</configuration>


对于知识的认知真的是每次都有不同的感受，以前的目标只是实现，无论怎么样只要实现就好，有很多地方都是不理解的，现在再去看那些代码感觉理解起来轻松了很多。敲代码的过程中感触最大的就是java和net平台的区别。通过这段时间做DRP的经历明显感觉net简直是傻瓜化的操作，而java操作起来就要烦人的多，也许现在还是对java的IDE不太熟悉吧。

作者：beijiguangyong 发表于2012-1-14 1:11:25 原文链接
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