机房收费系统重构之策略模式

      一、前言

      前面我们学习了23种设计模式，只是一直没用过，这次机房重构就是让我们将学习的这些理论应用与实践。首先，机房收费的主要功能就是上机收费，一说的收费就会有针对普通用户和会员等，实行不同的收费方法，这时我们就须要用到策略模式了。

      二、回想

       策略模式定义了一系列的算法，并将每个算法封装起来，并且使它们还能够相互替换。策略模式让算法独立于使用它的客户而独立变化。

                 

详见：设计模式 ( 十八 ) 策略模式Strategy（对象行为型）

      三、代码实现（为了方便，将整个下机过程的代码所有给出）

      1、U层中下机button的代码

    ''' <summary>
    ''' 下机功能
    ''' </summary>
    ''' <param name="sender"></param>
    ''' <param name="e"></param>
    ''' <remarks></remarks>
    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click

        Dim facadeSystem As New FacadeSystem
        Dim cardEntity As New CardEntity

        Try
            cardEntity.CardId = txtCardId.Text            '传參

            Dim returnOnList As ArrayList

            '调用外观,实现下机
            returnOnList = facadeSystem.StudentOff(cardEntity)

            '提出返回的数据
            Dim returnStudentEntity As StudentEntity
            Dim returnLineRecordEntity As LineRecordEntity
            Dim returnCardEntity As CardEntity

            returnStudentEntity = returnOnList.Item(0)
            returnLineRecordEntity = returnOnList.Item(1)
            returnCardEntity = returnOnList.Item(2)

            '显示学生信息
            txtStudentId.Text = returnStudentEntity.StudentId
            txtName.Text = returnStudentEntity.StudentName
            txtSex.Text = returnStudentEntity.Sex
            txtClass.Text = returnStudentEntity.Classes
            txtDepartment.Text = returnStudentEntity.Department
            txtExplan.Text = returnStudentEntity.Explain
            txtGrade.Text = returnStudentEntity.Grade
            '显示上机信息
            txtOnTime.Text = returnLineRecordEntity.OnTime
            txtOffTime.Text = returnLineRecordEntity.OffTime
            txtConsumeCash.Text = returnLineRecordEntity.ConsumeCash
            txtConsumeTime.Text = returnLineRecordEntity.ConsumeTime
            txtRemainCash.Text = returnCardEntity.RemainCash

            '显示上机人数
            lbOnPeople.Text = facadeSystem.RefreshOnPeople()

            '显示上机成功
            lbInformation.Text = "欢迎下次光临！"

        Catch ex As Exception
            MsgBox(ex.Message)
        End Try

    End Sub

      2、外观层代码

		''' <summary>
		''' 学生下机
		''' </summary>
        Public Function StudentOff(ByVal cardEntity As CardEntity) As ArrayList
            Try
                Dim cardBLL As New CardBLL
                Dim returnCardEntity As New CardEntity
                Dim returnBoolean As Boolean

                '检查卡号是否存在
                returnBoolean = cardBLL.QueryCard(cardEntity)
                If Not returnBoolean Then
                    Throw New Exception("卡号不存在！")
                End If

                '检查该卡号是否正在上机
                Dim lineRecordBll As New LineRecordBLL

                returnBoolean = lineRecordBll.GetOffStatus(cardEntity)
                If Not returnBoolean Then
                    Throw New Exception("该卡号还没上机！")
                End If

                '假设正在上机，就查到上机信息
                Dim lineRecordEntity As New LineRecordEntity

                lineRecordEntity = lineRecordBll.GetOff(cardEntity)

                '查看基础数据设定
                Dim basicDataEntity As New BasicDataEntity
                Dim basicDataBll As New BasicDataBLL

                basicDataEntity = basicDataBll.QueryAll()

                '计算消费时间
                Dim getDateBll As New GetDateBLL
                Dim strPrepareTime As Double
                Dim consumeTime As Double

                lineRecordEntity.OffTime = getDateBll.GetSqlTime()                                                                      '获取下机时间

                strPrepareTime = getDateBll.changeForHour(basicDataEntity.PrepareTime)                                                  '将准备时间转换为以小时为单位
                consumeTime = getDateBll.TimeToHour(lineRecordEntity.OffTime) - getDateBll.TimeToHour(lineRecordEntity.OnTime)          '计算消费时间

                '推断消费时间是否大于准备时间
                If consumeTime < strPrepareTime Then
                    lineRecordEntity.ConsumeTime = "0.0"
                Else
                    lineRecordEntity.ConsumeTime = CStr(consumeTime - strPrepareTime)
                End If

                '计算消费金额
                Dim strStudentLevel As String = "GeneralUser"   '用来实例化详细的计费方法
                Dim cashContext As CashContext

                cashContext = New CashContext(strStudentLevel)   '实例化计费方法的类
                lineRecordEntity.ConsumeCash = CStr(cashContext.GetResult(basicDataEntity, lineRecordEntity))

                '其它參数
                lineRecordEntity.OffDate = getDateBll.GetSqlDate()
                lineRecordEntity.OffStatus = "正常下机"
                lineRecordEntity.Local = System.Net.Dns.GetHostName().ToString

                '记录为正常下机
                lineRecordBll.AddOff(lineRecordEntity)

                '改动卡上剩余金额
                cardEntity = cardBLL.QueryAll(cardEntity)
                cardEntity.RemainCash = CStr(CDbl(cardEntity.RemainCash) - CDbl(lineRecordEntity.ConsumeCash))

                cardBLL.ModifyRemainCash(cardEntity)

                '查询学生实体
                Dim studentEntity As New StudentEntity
                Dim studentBll As New StudentBLL

                studentEntity.StudentId = cardEntity.CardId
                studentEntity = studentBll.QueryAll(studentEntity)

                '封装，传回
                Dim returnOnList As New ArrayList

                returnOnList.Add(studentEntity)
                returnOnList.Add(lineRecordEntity)
                returnOnList.Add(cardEntity)

                Return returnOnList

            Catch ex As Exception
                Throw
            End Try

        End Function

      3、cashContent类（相当于策略模式图中的Context类

''' <summary>
	''' 策略模式中的context类，用一个详细计费方法来配置，维护一个对抽象计费方法对象的引用
	''' </summary>
	Public Class CashContext


		''' <summary>
		''' 声明一个计算消费金额的抽象类
		''' </summary>
        Private cashSuper_ As CashSuper
        Private _strStudentLevel As String



		''' <summary>
		''' 声明一个计算消费金额的抽象类
		''' </summary>
		Private Property cashSuper() As CashSuper
			Get
                Return cashSuper_
			End Get
			Set(ByVal Value as CashSuper)
                cashSuper_ = Value
			End Set
		End Property

		''' <summary>
		''' 通过构造方法，传入详细的收费策略
		''' </summary>
        ''' <param name="strStudentLevel">初始化时，传入一个详细的收费策略</param>

        Sub New(strStudentLevel As String)

            Try
                '利用反射创建详细的算法
                Dim AssemblyName As String = "BLL"
                Dim className As String = AssemblyName + ".BLL." + strStudentLevel + "ConsumeCash"

                Me.cashSuper_ = CType(Assembly.Load(AssemblyName).CreateInstance(className), CashSuper)

            Catch ex As Exception
                Throw
            End Try

        End Sub

        ''' <summary>
        ''' 依据不同的收费策略，获得计算结果
        ''' </summary>
        ''' <param name="basicDataEntity"></param>
        ''' <param name="lineRecordEntity"></param>
        ''' <returns></returns>
        ''' <remarks></remarks>
        Public Function GetResult(ByVal basicDataEntity As BasicDataEntity, ByVal lineRecordEntity As LineRecordEntity) As Double

            Try
                Dim returnDouble As Double
                returnDouble = cashSuper_.CountConsumeCash(basicDataEntity, lineRecordEntity)

                Return returnDouble

            Catch ex As Exception
                Throw
            End Try


        End Function


	End Class ' CashContext

      4、CashSuper抽象类（相相当于策略模式图中的Strategy类

	''' <summary>
    ''' 策略模式，封装计算方法的抽象类
	''' </summary>
    Public MustInherit Class CashSuper


        ''' <summary>
        ''' 计算消费金额的计算方法
        ''' </summary>
        ''' <param name="lineRecordEntity">上机记录表的实体</param>
        ''' <param name="basicDataEntity">数据库数据表实体</param>
        Public MustOverride Function CountConsumeCash(ByVal basicDataEntity As BasicDataEntity, ByVal lineRecordEntity As LineRecordEntity) As Double


    End Class ' CashSuper

      5、GeneralUserConsumeCash类（相相当于策略模式图中的CreateStrategy类，详细收费方法

	''' <summary>
	''' 计算一般用户消费的方法
	''' </summary>
	Public Class GeneralUserConsumeCash
		Inherits BLL.CashSuper


	''' <summary>
	''' 计算消费金额的计算方法
	''' </summary>
        ''' <param name="lineRecordEntity">上机记录表的实体</param>
        ''' <param name="basicDataEntity">数据库数据表实体</param>
        Public Overrides Function CountConsumeCash(ByVal basicDataEntity As BasicDataEntity, ByVal lineRecordEntity As LineRecordEntity) As Double

            Try
                Dim returnMoney As Double
                Dim countTime As Integer           '表示多少个单位时间
                Dim oneMinuteMoney As Double       '每分钟消费的钱

                oneMinuteMoney = CDbl(basicDataEntity.UnitCash) / 60

                '推断是否在规定上机时间内
                If lineRecordEntity.ConsumeTime > basicDataEntity.LeastTime Then         '假设超过至少上机时间
                    '单位时间的个数=（消费时间-至少上机时间）/单位时间
                    countTime = CInt(Int((CDbl(Minute(CDate(lineRecordEntity.ConsumeTime))) - CDbl(basicDataEntity.LeastTime)) / basicDataEntity.UnitTime + 0.9999))
                    '消费金额=（单位时间个数*单位时间+至少上机时间）*每分钟消费的钱
                    returnMoney = (countTime * basicDataEntity.UnitTime + CDbl(basicDataEntity.LeastTime)) * oneMinuteMoney
                    Return returnMoney
                Else                                                                     '假设没有超过至少上机时间
                    '至少上机时间乘以单位时间的钱
                    returnMoney = CDbl(basicDataEntity.LeastTime) * oneMinuteMoney
                    Return returnMoney
                End If

            Catch ex As Exception
                Throw
            End Try

        End Function


	End Class ' GeneralUserConsumeCash

      四、讲解运行过程

       首先，将 "GeneralUser"传给变量strStudentLevel，作用是在Dim className As String = AssemblyName + ".BLL." + strStudentLevel + "ConsumeCash"这句话中，利用反射创建详细的收费方法，即普通用户的收费方法GeneralUserConsumeCash类。

       然后，调用cashContext.GetResult()方法，此方法又调用抽象类cashSuper的计算消费金额CountConsumeCash
的方法，因为此方法在子类中被重写，所以最后运行详细收费类GeneralUserConsumeCash的CountConsumeCash方法，从而得出结果。

      五、总结

      本来能够通过訪问配置文件向cashContext中传入參数，从而推断详细的收费方法，这样当我们须要改动收费方法的时候直接改动配置文件即可了，使我们的维护更加的方便。因为这次仅仅使用了普通用户，所以计费方法仅仅有一种，仅仅採用的strStudentLevel变量传參，大大降低了系统的可维护性。所以在以后，我们做系统的时候一定要注意，尽量降低系统的耦合度，从而创造出更加优秀的产品。