七层登录实现
七层登录实现
机房重构刚开始的七层登录，刚开始其中有很多的地方都不理解，后来通过查资料，看博客，问同学慢慢的明白一点了。
七层就是在三层的基础之上，添加了外观层——设计模式的外观模式，抽象工厂加反射，接口层。
外观层：主要是把UI和BLL层分离。
抽象工厂加反射：主要是为了更换数据库的方便性，同时把DAL层中的类转换成为IDAL层中的接口，从而使BLL层实现通过调用IDAL从而调用DAL层。
接口层：把BLL和DAL分离。
这样，当需要改动系统的时候，非常的方便，使用七层做到了大大的解耦和，当有新的需求出现的时候或者在后期的系统维护时，仅仅需要改动某一层就可以，或者具体到某一层中的某一个类就可以，而不至于牵一发而动全身，提高了系统的可扩展性，可维护性和灵活性。
UML中一共有四大关系，即关联、依赖、泛化和实现，这里用到了三种，即关联、依赖和实现。
七层从UI层开始，逐层依赖于下一层，除了SqlHelper和Factory之外的所有的层，都要添加对Entity层的引用，这里是关联关系，因为所有的层在使用实体层的时候，首先都先要对实体进行实例化，即New一个实体，所以暂时理解为关联关系（最普通的关联关系，不是聚合也不是组合关系），而DAL层实现的是IDAL层中的方法，同时依赖于SqlHelper实现它自己的功能。
各层的具体代码：
UI层
<span style="font-size:24px;"><span style="font-size:24px;">Public Class FrmLogin
Private Sub btnLogin_Click(sender As Object, e As EventArgs) Handles btnLogin.Click
'判断文本框是否为空
If txtUserID.Text = "" Then
MessageBox.Show("请您输入用户名！", "", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
txtUserID.Focus()
Exit Sub
ElseIf txtPWD.Text = "" Then
MessageBox.Show("请您输入密码！", "", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
txtPWD.Focus()
Exit Sub
End If
'实例化实体类
'把用户名和密码放到实体中
Dim User As New Entity.T_UserEntity
User.UserID = txtUserID.Text.Trim()
User.PWD = txtPWD.Text.Trim()
Dim Result As String
Dim facade As New Facade.LoginFacade
Result = facade.Login(User)
'用户名和密码验证的几种情况
Select Case Result
Case "此用户不存在"
MsgBox("此用户不存在，请重新输入用户名！")
txtUserID.Focus()
txtUserID.SelectAll()
Case "密码错误"
MsgBox("密码错误，请重新输入密码！")
txtPWD.Focus()
txtPWD.SelectAll()
Case "登陆成功"
MsgBox("恭喜您，登录成功！")
NowUser = txtUserID.Text.Trim()
FrmMain.Show()
Me.Hide()
End Select
End Sub
Private Sub btnCancel_Click(sender As Object, e As EventArgs) Handles btnCancel.Click
End
End Sub
End Class</span></span>
Façade层
<span style="font-size:24px;"><span style="font-size:24px;">Public Class LoginFacade
Public Function Login(ByVal User As Entity.T_UserEntity) As String
Dim Userbll As New BLL.LoginBLL
'调用B层的方法验证用户名和密码是否正确
If Userbll.CheckUser(User) = False Then
Return "此用户不存在"
Else
If Userbll.CheckPWD(User) = False Then
Return "密码错误"
Else
Return "登陆成功"
End If
End If
End Function
End Class</span></span>
BLL层
<span style="font-size:24px;"><span style="font-size:24px;">Public Class LoginBLL
'验证用户名是否正确
Public Function CheckUser(ByVal user As Entity.T_UserEntity) As Boolean
Dim Iuser As IDAL.LoginIDAL
Dim factory As New Factory.LoginFactory
Iuser = factory.CreateUserDAO()
Dim mylist As New List(Of Entity.T_UserEntity)
mylist = Iuser.SelectUserID(user)
If mylist.Count = 0 Then
Return False
Else
Return True
End If
End Function
'验证密码是否正确
Public Function CheckPWD(ByVal password As Entity.T_UserEntity) As Boolean
Dim Iuser As IDAL.LoginIDAL
Dim factory As New Factory.LoginFactory
Iuser = factory.CreateUserDAO
Dim mylist As New List(Of Entity.T_UserEntity)
mylist = Iuser.SelectPWD(password)
If mylist.Count = 0 Then
Return False
Else
Return True
End If
End Function
End Class</span></span>
Factory层
<span style="font-size:24px;"><span style="font-size:24px;">Imports System.Reflection
Imports System.Configuration
'连接数据库时采用了抽象工厂加反射
'抽象工厂，负责数据库的选择和创建接口
Public Class LoginFactory
Dim DB As String = System.Configuration.ConfigurationSettings.AppSettings("DBss")
Private Shared ReadOnly assemblyName = "DAL"
Public Function CreateUserDAO() As IDAL.LoginIDAL
'返回接口
Dim className As String = assemblyName + "." + DB + "LoginDAL"
Return CType(Assembly.Load(assemblyName).CreateInstance(className), IDAL.LoginIDAL)
End Function
End Class</span></span>
IDAL层
<span style="font-size:24px;"><span style="font-size:24px;">'接口IDAL
Public Interface LoginIDAL
Function SelectUserID(ByVal User As Entity.T_UserEntity) As List(Of Entity.T_UserEntity)
Function SelectPWD(ByVal User As Entity.T_UserEntity) As List(Of Entity.T_UserEntity)
End Interface</span></span>
DAL层
<span style="font-size:24px;"><span style="font-size:24px;">Imports System.Data
Imports System.Data.SqlClient
Imports Entity
'D层用来将接口实例化
Public Class SqlServerLoginDAL : Implements IDAL.LoginIDAL
Public Function SelectUserID(User As Entity.T_UserEntity) As List(Of Entity.T_UserEntity) Implements IDAL.LoginIDAL.SelectUserID
Dim sqlParams As SqlParameter() = {New SqlParameter("@UserID", User.UserID)}
Dim strSql As String = "select*from T_User where UserID=@UserID"
'实例化SqlHelper
Dim helper As New SqlHelper
Dim table As New DataTable
Dim mylist As New List(Of Entity.T_UserEntity)
table = helper.GetDataTable(strSql, CommandType.Text, sqlParams)
mylist = ConvertHelper.ConvertList(Of Entity.T_UserEntity)(table)
'返回泛型
Return mylist
End Function
Public Function SelectPWD(User As Entity.T_UserEntity) As List(Of Entity.T_UserEntity) Implements IDAL.LoginIDAL.SelectPWD
Dim sqlParams As SqlParameter() = {New SqlParameter("@UserID", User.UserID), New SqlParameter("@PWD", User.PWD)}
Dim strSql As String = "select*from T_User where UserID=@UserID and PWD=@PWD"
'实例化SqlHelper
Dim helper As New SqlHelper
Dim table As New DataTable
Dim mylist As New List(Of Entity.T_UserEntity)
table = helper.GetDataTable(strSql, CommandType.Text, sqlParams)
mylist = ConvertHelper.ConvertList(Of Entity.T_UserEntity)(table)
'返回泛型
Return mylist
End Function
End Class</span></span>
Entity层
<span style="font-size:24px;"><span style="font-size:24px;">Public Class T_UserEntity
'定义变量
Private _UserID As String
Private _PWD As String
Private _Level As String
Private _UserName As String
Private _Head As String
Public Property UserID As String
Get
Return _UserID
End Get
Set(value As String)
_UserID = value
End Set
End Property
Public Property PWD As String
Get
Return _PWD
End Get
Set(value As String)
_PWD = value
End Set
End Property
Public Property Level As String
Get
Return _Level
End Get
Set(value As String)
_Level = value
End Set
End Property
Public Property UserName As String
Get
Return _UserName
End Get
Set(value As String)
_UserName = value
End Set
End Property
Public Property Head As String
Get
Return _Head
End Get
Set(value As String)
_Head = value
End Set
End Property
End Class</span></span>
泛型返回的是整张数据表，比如查询正在上机的所有学生等等，需要的是一个数据表中所有的数据时，才使用泛型。