机房重构—七层登录

        七层登录，是三层登录演化而来的，它的主要目的是为了解耦和，让程序耦合性底，不必依赖性太强。它比三层多了外观层（Facade），工厂层（Factory）和接口层（IDAL）。多了这几层的应用，让程序更加符合开放封闭原则，大大降低程序的耦合性。

下面就是七层登录的代码：

首先用来连接数据库的配置文件：

       通过配置文件可以很方便的更改数据库，如果需要更改数据库，我只需要把配置文件中的Sqlserver改成其他数据库名字就可以了（比如MySQL等）。

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
  </configSections>
  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
  </startup>
  <appSettings>
    <add key="DB"  value="DAL"/>
    <add key="strConnection"  value="Server=.;Database=login;User ID=sa;Password=123456" />
  </appSettings>
</configuration>

UI层:

Private Sub btnOK_Click(sender As Object, e As EventArgs) Handles btnOK.Click
        '输入不能为空
        If txtUserName.Text = "" Then
            MsgBox("请输入用户名", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
            txtUserName.Focus()
        End If
        If IsNumeric(txtUserName.Text) = False Then
            MsgBox("用户名请输入数字", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
            txtUserName.Text = ""
        End If
        If txtPassword.Text = "" Then
            MsgBox("请输入密码", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
            txtPassword.Focus()
        End If
        Entity.LoginEntity.ID = txtUserName.Text.Trim
        Try
            Dim Facade As New Facade.LoginFacade
            Dim UserInfo As New Entity.LoginEntity
            UserInfo.UserID = txtUserName.Text.Trim
            UserInfo.Password = txtPassword.Text
            Dim strResult As Boolean
            '将U层的用户信息传入外观层，然后通过外观层传入B层进行判断
            strResult = Facade.CheckUser(UserInfo)

            txtUserName.Text = ""
            txtPassword.Text = ""

            Dim table As DataTable
            table = Facade.CheckPwd(UserInfo)

            Me.Hide()
            txtPassword.Text = ""
            txtUserName.Text = ""
            frmMain.Show()

        Catch ex As Exception
            MsgBox("用户不存在或密码不正确")
            txtPassword.Text = ""
            txtUserName.Text = ""
        End Try
    End Sub

D层：

Imports System.Data.SqlClient  'system.Data.SqlClient 命名空间是SQLSever的.NET Framework数据提供程序
'SQL Sever 的.NET Framework数据提供程序描述了一个类集合，这个类集合用于访问托管空间中的SQL Sever数据库
Imports Entity
Imports IDAL
'Imports System.Configuration
Imports SqlHelper
Public Class LoginDAL : Implements IDAL.LoginIDAL
    '实现接口中的方法
    Private sqlHelper As New SqlHelper.SqlHelper
    '判断用户名是否存在
    Public Function selectUser(UserInfo As LoginEntity) As DataTable Implements LoginIDAL.selectUser
        Dim sql As String  '中间变量，用于储存从数据库中查找到的信息
        Dim table As DataTable  '声明一个DataTable
        '声明并实例化参数数组
        Dim sqlParams As SqlParameter() = {New SqlParameter("@UserID", UserInfo.UserID),
                                           New SqlParameter("@Password", UserInfo.Password)}
        sql = "select * from User_info where UserID=@UserID and Password=@Password"
        '调用SqlHelper类中的GetDataTable（）方法来执行查询，并获取返回值
        table = sqlHelper.ExecSelect(sql, CommandType.Text, sqlParams)
        Return table
    End Function
End Class

工厂层：

Imports System.Reflection '添加对反射的引用
Imports System.Configuration '添加对配置文件的引用
Imports System.Data
Imports IDAL '引用接口层
'反射+配置文件+抽象工厂实现数据访问
Public Class LoginFactory
    Private Shared ReadOnly AssemblyName As String = "DAL" '数据程序集名称&命名空间DAL
    Dim strDB As String = System.Configuration.ConfigurationSettings.AppSettings("DB")
    Public Function CreateIUser() As LoginIDAL
        Dim classname As String = strDB + "." + "LoginDAL" '要实例化的D层的类的名称
        Dim IUser As LoginIDAL
        'CType函数将返回表达式显示地转换为指定的数据类型、对象、结构、类或接口后的结果
        IUser = CType(Assembly.Load(AssemblyName).CreateInstance(classname), LoginIDAL) '返回LoginIDAL
        Return IUser
    End Function
End Class

接口层：

Public Interface LoginIDAL
    '判断用户名是否存在
    Function selectUser(ByVal UserInfo As Entity.LoginEntity) As DataTable
End Interface

B层：

Imports IDAL
Public Class LoginBLL
    '检查用户是否存在
    Public Function ExistUser(ByVal UserInfo As Entity.LoginEntity) As Boolean
        Dim Factory As New Factory.LoginFactory
        Dim IUser As IDAL.LoginIDAL
        '调用创建用户的工厂方法
        IUser = Factory.CreateIUser() '调用工厂的CreatIUser方法创建IUser接口实例
        Dim table As New DataTable '中间变量，用于存储D层查询到的数据
        Dim flag As Boolean
        table = IUser.selectUser(UserInfo)
        If table.Rows.Count = 0 Then
            flag = False
        Else
            flag = True
        End If
        Return flag
    End Function
    '查看密码是否正确
    Public Function RightPWD(ByVal UserInfo As Entity.LoginEntity) As DataTable
        Dim Factory As New Factory.LoginFactory
        Dim IUser As IDAL.LoginIDAL
        Dim table As DataTable '中间变量，用于存储D层查询到的数据

        IUser = Factory.CreateIUser '调用工厂的方法创建Iuser
        table = IUser.selectUser(UserInfo) '调用接口的方法selectUser
        If UserInfo.Password = Trim(table.Rows(0).Item(1)) Then
            MsgBox("登陆成功!")
        End If
        Return table
    End Function
End Class

外观层：

Public Class LoginFacade
    '检查用户是否存在
    Public Function CheckUser(ByVal UserInfo As Entity.LoginEntity) As Boolean
        Dim IsUserExists As New BLL.LoginBLL
        Dim flag As Boolean
        flag = IsUserExists.ExistUser(UserInfo)
        If flag = True Then
            Return True
        Else
            Return False
        End If
    End Function
    '检查密码是否正确
    Public Function CheckPwd(ByVal UserInfo As Entity.LoginEntity) As DataTable
        Dim IsPwdExists As New BLL.LoginBLL
        Dim table As DataTable
        table = IsPwdExists.RightPWD(UserInfo)
        Return table
    End Function
End Class

实体层：

Public Class LoginEntity
    Public Shared ID As String '用于记录登录时的用户名
    Private _UserID As String
    Public Property UserID As String
        Get
            Return _UserID
        End Get
        Set(value As String)
            _UserID = value
        End Set
    End Property
    Private _password As String
    Public Property Password As String
        Get
            Return _password
        End Get
        Set(value As String)
            _password = value
        End Set
    End Property
End Class

最后是七层登录的顺序图：