Session Management in Web Garden using Custom Components and VB.NET

Public Class SessionManager
Implements ISessionManager 'ToDo: Add Implements Clauses for implementation methods of these interface(s)
'Hashtable to store the list of sessions allocated.
Private hsSession As New Hashtable
Private Shared objSM As SessionManager 'static SINGLETON object
'a timer to manage the session timeouts
Private Shared tmrSessionTimeout As Timer
'Private Constructor-To prevent creating instaces explicitly
Private Sub New()
End Sub 'New

'Create a new object of session manager.
Public Shared Function getInstance() As SessionManager
If objSM Is Nothing Then
objSM = New SessionManager
'create a new objectof the timer class and associte //a timer call back delegate. The removesession
'method will be invoked by the timer object for //every 1000 milliseconds (change it as u like).
tmrSessionTimeout = New Timer(New TimerCallback(objSM.removesession), Nothing, 0, 100)
Return objSM
End If
Return objSM
End Function 'getInstance

'This method will be invoked by the timer call back for every 1000 milliseconds.
Private Sub removesession(ByVal state As Object)
Dim objSesEnum As IDictionaryEnumerator = hsSession.GetEnumerator()
'A temporary session object.
Dim tmpSesObj As ISession
Dim arrExpiredKeys As New ArrayList
'for each session, check the last used datetime.
While objSesEnum.MoveNext()
'The session will be removed, if the user is idle for 2 hours. (change it as u like).
tmpSesObj = CType(objSesEnum.Value, ISession)
Dim dt As DateTime = DateTime.Parse(tmpSesObj.getAttribute("lastAccessedDatetime").ToString())
Dim ts As TimeSpan = dt.Subtract(DateTime.Now)
'If the difference between the last accessed //datetime and current date time is equal to 2 hours //then the session id will be added to the arraylist.
'(ie., left idle for 2 hours)
If dt.Subtract(DateTime.Now).Hours >= 2 Then
arrExpiredKeys.Add(objSesEnum.Key)
End If
'remove the list of keys added to the array list.
Dim i As Integer = 0
While arrExpiredKeys.Count > i
'remove the session from the hashtable.
hsSession.Remove(arrExpiredKeys(i))
End While
End While
End Sub 'removesession 

Public Function createSessionId() As String
'Create a new guid which will act as the session id
Dim newSessionId As String = Guid.NewGuid().ToString
'create a new session object and store the object in the //hashtable against the new session id (GUID).
Dim objS As New Session
hsSession.Add(newSessionId, objS)
'Set the session id into the session object.
objS.setAttribute("SessionId", newSessionId)
'return the session id,
Return newSessionId
End Function 'createSessionId 

Public Function getSession(ByVal strSesId As String) As ISession
Dim objS As ISession = CType(hsSession(strSesId), ISession)
'everytime when the session object is retried, update the //lastaccesseddate variable with the latest datetime
objS.setAttribute("lastAccessedDatetime", DateTime.Now)
Return objS 'return the session object
End Function 'getSession 

Public Function removeSession(ByVal strSesId As String) As ISession
Dim objS As ISession = CType(hsSession(strSesId), ISession)
'remove the sessionid from the hash table.
hsSession.Remove(strSesId)
Return objS 'return the removed session
End Function 'removeSession
End Class 'SessionManager

Step 3: Implement the ISession interface.

Public Class Session
Implements ISession
'ToDo: Add Implements Clauses for implementation methods of these interface(s)
'Hashtable to store the values..
Private hsValues As New Hashtable
'Default constructor
Public Sub New()
End Sub 'New

Public Function removeAttribute(ByVal strKey As String) As Object
Dim obj As Object = hsValues(strKey) 'fetch the value
hsValues.Remove(strKey)
Return obj 'return the value that is removed
End Function 'removeAttribute

Public Function getAttribute(ByVal strKey As String) As Object
'get the value for the key specified
Return hsValues(strKey)
End Function 'getAttribute

Public Sub setAttribute(ByVal strKey As String, ByVal objValue As [Object])
'add a new value, if the key already exists then it will //be overridden
hsValues.Add(strKey, objValue)
End Sub 'setAttribute 
End Class 'Session

At any time there will be only one instance of the session manager class (as it is declared as static). It must always remain as a singleton object, as persistent storage and maintenance of multiple sessions cannot be achieved otherwise. A new static method getInstance is added into the SessionManager class to create a new instance of the SessionManager class. The constructor of the class is made private to prevent creating objects of the SessionManager component explicitly.

Testing the Session Manager component.

Now we can test the session manager component. Create a new console application project and add a reference of the SessionManager component. The following code snippet creates an object of the session manager class (using the getInstance method) and assigns a value in the session object. The WriteLine method prints the value in the session object.

Imports NpSessionManager 'add the namespace
Friend Class SessionManagerTest
Private Shared strid As String
<STAThread()> _
Shared Sub Main(ByVal args As String())
'Create a new session and assign values to the session object.
Dim sm As SessionManager = SessionManager.getInstance()
'store the session id in some global variable.
strid = CStr(sm.createSessionId())
'get the session
Dim objS As ISession = CType(sm.getSession(strid), ISession)
objS.setAttribute("website", "c-sharpcorner")
Console.WriteLine(objS.getAttribute("website").ToString())
Console.ReadLine()
End Sub
End Class

Scalibility and deploying the component.

Due to the object oriented design of the session manager component, any amount of flexibility and scalability is achievable.