SessionStateUtility Class

 

Provides helper methods used by session-state modules and session-state store providers to manage session information for an ASP.NET application. This class cannot be inherited.

Namespace:   System.Web.SessionState
Assembly:  System.Web (in System.Web.dll)

System.Object
  System.Web.SessionState.SessionStateUtility

Public NotInheritable Class SessionStateUtility

NameDescription
System_CAPS_pubpropertySystem_CAPS_staticSerializationSurrogateSelector

Gets or sets a serialization surrogate selector that is used for session serialization customization.

NameDescription
System_CAPS_pubmethodSystem_CAPS_staticAddHttpSessionStateToContext(HttpContext, IHttpSessionState)

Applies the session data to the context for the current request.

System_CAPS_pubmethodSystem_CAPS_staticGetHttpSessionStateFromContext(HttpContext)

Retrieves session data from the context for the current request.

System_CAPS_pubmethodSystem_CAPS_staticGetSessionStaticObjects(HttpContext)

Gets a reference to the static objects collection for the specified context.

System_CAPS_pubmethodSystem_CAPS_staticIsSessionStateReadOnly(HttpContext)

Gets a value which indicates whether the session state is read-only for the specified HttpContext.

System_CAPS_pubmethodSystem_CAPS_staticIsSessionStateRequired(HttpContext)

Gets a value which indicates whether the session state is required for the specified HttpContext.

System_CAPS_pubmethodSystem_CAPS_staticRaiseSessionEnd(IHttpSessionState, Object, EventArgs)

Executes the Session_OnEnd event defined in the Global.asax file for the ASP.NET application.

System_CAPS_pubmethodSystem_CAPS_staticRemoveHttpSessionStateFromContext(HttpContext)

Removes session data from the specified context.

The SessionStateUtility class provides static helper methods that are used by a session-state module or a session-state store provider. Application developers will not need to call these methods from their code.

The following table describes the ways the session-state module and session-state store provider use the methods.

Method

Use

GetHttpSessionStateFromContext method

Can be used by custom session-state modules to either retrieve session information for an existing session or create session information for a new session.

AddHttpSessionStateToContext method

Called by the session-state module to add the session data to the current HttpContext and make it available to application code through the Session property.

RemoveHttpSessionStateFromContext method

Called by the session-state module during the ReleaseRequestState or EndRequest events at the end of a request, to clear session data from the current HttpContext.

GetSessionStaticObjects method

Called by the session-state module to get a reference to the StaticObjects collection based on objects defined in the Global.asax file. The HttpStaticObjectsCollection collection returned is included with the session data added to the current HttpContext.

Session data is passed to and retrieved from the current HttpContext as an HttpSessionStateContainer object or any valid implementation of the IHttpSessionState interface.

For information about implementing a session-state store provider, see Implementing a Session-State Store Provider.

The following code example shows a custom session-state module implementation that stores session information in memory using a Hashtable. The module uses the SessionStateUtility class to reference the current HttpContext and SessionIDManager, retrieve the current HttpStaticObjectsCollection, and raise the Session_OnEnd event defined in the Global.asax file for the ASP.NET application. This application does not prevent simultaneous Web requests from using the same session identifier.

Imports System
Imports System.Web
Imports System.Web.SessionState
Imports System.Collections
Imports System.Threading
Imports System.Web.Configuration
Imports System.Configuration

Namespace Samples.AspNet.SessionState

    Public NotInheritable Class MySessionStateModule
        Implements IHttpModule, IDisposable

        Private pSessionItems As Hashtable = New Hashtable()
        Private pTimer As Timer
        Private pTimerSeconds As Integer = 10
        Private pInitialized As Boolean = False
        Private pTimeout As Integer
        Private pCookieMode As HttpCookieMode = HttpCookieMode.UseCookies
        Private pHashtableLock As ReaderWriterLock = New ReaderWriterLock()
        Private pSessionIDManager As ISessionIDManager
        Private pConfig As SessionStateSection


        ' The SessionItem class is used to store data for a particular session along with
        ' an expiration date and time. SessionItem objects are added to the local Hashtable
        ' in the OnReleaseRequestState event handler and retrieved from the local Hashtable
        ' in the OnAcquireRequestState event handler. The ExpireCallback method is called
        ' periodically by the local Timer to check for all expired SessionItem objects in the
        ' local Hashtable and remove them. 
        Private Class SessionItem
            Friend Items As SessionStateItemCollection
            Friend StaticObjects As HttpStaticObjectsCollection
            Friend Expires As DateTime
        End Class



        '
        ' IHttpModule.Init
        '

	Public Sub Init(ByVal app As HttpApplication) Implements IHttpModule.Init
            ' Add event handlers.
            AddHandler app.AcquireRequestState, New EventHandler(AddressOf Me.OnAcquireRequestState)
            AddHandler app.ReleaseRequestState, New EventHandler(AddressOf Me.OnReleaseRequestState)

            ' Create a SessionIDManager.
            pSessionIDManager = New SessionIDManager()
            pSessionIDManager.Initialize()

            ' If not already initialized, initialize timer and configuration.
            If Not pInitialized Then
                SyncLock GetType(MySessionStateModule)
                    If Not pInitialized Then
                        ' Create a Timer to invoke the ExpireCallback method based on
                        ' the pTimerSeconds value (e.g. every 10 seconds).
                        pTimer = New Timer(New TimerCallback(AddressOf Me.ExpireCallback), _
                                           Nothing, _
                                           0, _
                                           pTimerSeconds * 1000)

                        ' Get the configuration section and set timeout and CookieMode values.
                        Dim cfg As System.Configuration.Configuration = _
                          WebConfigurationManager.OpenWebConfiguration( _
                            System.Web.Hosting.HostingEnvironment.ApplicationVirtualPath)
                        pConfig = CType(cfg.GetSection("system.web/sessionState"), SessionStateSection)

                        pTimeout = CInt(pConfig.Timeout.TotalMinutes)
                        pCookieMode = pConfig.Cookieless

                        pInitialized = True
                    End If
                End SyncLock
            End If
        End Sub



        '
        ' IHttpModule.Dispose
        '
        Public Sub Dispose() Implements IHttpModule.Dispose, IDisposable.Dispose
            If Not pTimer Is Nothing Then CType(pTimer, IDisposable).Dispose()
        End Sub


        '
        ' Called periodically by the Timer created in the Init method to check for 
        ' expired sessions and remove expired data.
        '
        Sub ExpireCallback(ByVal state As Object)
            Try
                pHashtableLock.AcquireWriterLock(Int32.MaxValue)

                Me.RemoveExpiredSessionData()

            Finally
                pHashtableLock.ReleaseWriterLock()
            End Try

        End Sub

        '
        ' Recursivly remove expired session data from session collection.
        '
        Private Sub RemoveExpiredSessionData()
            Dim sessionID As String
            Dim entry As DictionaryEntry

            For Each entry In pSessionItems
                Dim item As SessionItem = CType(entry.Value, SessionItem)

                If DateTime.Compare(item.Expires, DateTime.Now) <= 0 Then
                    sessionID = entry.Key.ToString()
                    pSessionItems.Remove(entry.Key)

                    Dim stateProvider As HttpSessionStateContainer = _
                      New HttpSessionStateContainer(sessionID, _
                                                   item.Items, _
                                                   item.StaticObjects, _
                                                   pTimeout, _
                                                   False, _
                                                   pCookieMode, _
                                                   SessionStateMode.Custom, _
                                                   False)

                    SessionStateUtility.RaiseSessionEnd(stateProvider, Me, EventArgs.Empty)
                    Me.RemoveExpiredSessionData()
                    Exit For
                End If
            Next entry
        End Sub



        '
        ' Event handler for HttpApplication.AcquireRequestState
        '
        Private Sub OnAcquireRequestState(ByVal [source] As Object, ByVal args As EventArgs)
            Dim app As HttpApplication = CType([source], HttpApplication)
            Dim context As HttpContext = app.Context
            Dim isNew As Boolean = False
            Dim sessionID As String
            Dim sessionData As SessionItem = Nothing
            Dim supportSessionIDReissue As Boolean = True

            pSessionIDManager.InitializeRequest(context, False, supportSessionIDReissue)
            sessionID = pSessionIDManager.GetSessionID(context)


            If Not (sessionID Is Nothing) Then
                Try
                    pHashtableLock.AcquireReaderLock(Int32.MaxValue)
                    sessionData = CType(pSessionItems(sessionID), SessionItem)

                    If Not (sessionData Is Nothing) Then
                        sessionData.Expires = DateTime.Now.AddMinutes(pTimeout)
                    End If
                Finally
                    pHashtableLock.ReleaseReaderLock()
                End Try
            Else
                Dim redirected, cookieAdded As Boolean

                sessionID = pSessionIDManager.CreateSessionID(context)
                pSessionIDManager.SaveSessionID(context, sessionID, redirected, cookieAdded)

                If redirected Then Return
            End If
            If sessionData Is Nothing Then
                ' Identify the session as a new session state instance. Create a new SessionItem
                ' and add it to the local Hashtable.
                isNew = True

                sessionData = New SessionItem()

                sessionData.Items = New SessionStateItemCollection()
                sessionData.StaticObjects = SessionStateUtility.GetSessionStaticObjects(context)
                sessionData.Expires = DateTime.Now.AddMinutes(pTimeout)

                Try
                    pHashtableLock.AcquireWriterLock(Int32.MaxValue)
                    pSessionItems(sessionID) = sessionData
                Finally
                    pHashtableLock.ReleaseWriterLock()
                End Try
            End If

            ' Add the session data to the current HttpContext.
            SessionStateUtility.AddHttpSessionStateToContext(context, _
                             New HttpSessionStateContainer(sessionID, _
                                                          sessionData.Items, _
                                                          sessionData.StaticObjects, _
                                                          pTimeout, _
                                                          isNew, _
                                                          pCookieMode, _
                                                          SessionStateMode.Custom, _
                                                          False))

            ' Execute the Session_OnStart event for a new session.
            If isNew Then RaiseEvent Start(Me, EventArgs.Empty)
        End Sub


        '
        ' Event for Session_OnStart event in the Global.asax file.
        '
	Public Event Start As EventHandler



        '
        ' Event handler for HttpApplication.ReleaseRequestState
        '
        Private Sub OnReleaseRequestState(ByVal [source] As Object, ByVal args As EventArgs)
            Dim app As HttpApplication = CType([source], HttpApplication)
            Dim context As HttpContext = app.Context
            Dim sessionID As String

            ' Read the session state from the context
            Dim stateProvider As HttpSessionStateContainer = _
               CType(SessionStateUtility.GetHttpSessionStateFromContext(context), HttpSessionStateContainer)

            ' If Session.Abandon() was called, remove the session data from the local Hashtable
            ' and execute the Session_OnEnd event from the Global.asax file.
            If stateProvider.IsAbandoned Then
                Try
                    pHashtableLock.AcquireWriterLock(Int32.MaxValue)

                    sessionID = pSessionIDManager.GetSessionID(context)
                    pSessionItems.Remove(sessionID)
                Finally
                    pHashtableLock.ReleaseWriterLock()
                End Try

                SessionStateUtility.RaiseSessionEnd(stateProvider, Me, EventArgs.Empty)
            End If

          SessionStateUtility.RemoveHttpSessionStateFromContext(context)
        End Sub

    End Class
End Namespace

To use this custom session-state module in an ASP.NET application, you can replace the existing SessionStateModule reference in the Web.config file, as shown in the following example.

<configuration>
  <system.web>
    <httpModules>
      <remove name="Session" />
      <add name="Session"
      type="Samples.AspNet.SessionState.MySessionStateModule" />
    </httpModules>
  </system.web>
</configuration>

.NET Framework
Available since 2.0

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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