ASP.NET 2.0 Training : Customizing the Session State Mechanism

In this tutorial you will learn about Extending the Session State Mechanism, The Default Session State Mechanism and its customization, Customizing the Session State Module and Writing a custom session state module

Extending the Session State Mechanism

The stateless HTTP protocol treats each page request independently and the server is unaware of the variable values of the earlier request. The session state is a dictionary based API that is used by developers to store user specific data for the duration of the session. The session state is enabled by default for all ASP.NET applications. In ASP.NET 2.0 developers can define custom stores for session states or customize session states in the existing ASP.NET session state mechanism. In the latter the customizable options are limited whereas in the former the developer has greater flexibility. In this section we shall examine both these options in great detail.

The Default Session State Mechanism and its customization

By default session variables are stored in a SessionStateItemCollection that is exposed through the System.Web.HttpContext.Session property. The collection is indexed by the name of the variable

Session["FirstName"] = FirstNameTextBox.Text;
Session["LastName"] = LastNameTextBox.Text;

The session variables can be of any valid .NET type such as ArrayList. Session identifiers are read using the SessionID property. Each page request is examined for a SessionID value and a new session starts only if no SessionID value is found. These values are stored in a cookie by default. However, the applications can be configured to store SessionID values in the URL as a cookieless session. Each session is active until the SessionID is terminated or timed out.

Session Events are raised when a new session is started or a session ends. The Session_OnStart event and Session_OnEnd events are raised at the start and end of the session respectively. These events are specified in the Global.asax file(web.config file) in the ASP.NET application. The session_OnEnd event is not supported if the session mode value is not set to InProc (the default mode).

The session mode defines the different storage options available for storing session variables. By default session variables are stored in the memory space of the ASP.NET worker process. The storage can be customized and the session mode can be set to off at the option of the developer.

The session state can be configured using the element of the System.web configuration section. The session can also be configured using the EnableSessionState page directive. This element allows the developer specify the mode in which the session will store data and the process by which identifier values will be sent to the server from the client and vice versa. It also helps define the timeout values and the supporting values that are based on the session mode.

he sessionState is exclusive to the session in ASP.NET. When two different users make concurrent requests to a page, separate sessions are granted concurrently. If two requests are made for a single sessionID, then the first request is granted exclusive access while the second request will be executed on release from the first request. If the request is for a readonly session mode then the both requests are granted simultaneously. However read write request will dominate a read only request and the latter must await the release of the sessionID by the former.

Customizing the Session State Module

Four aspects of the session state module can be customized by the developer. The first of these is the Session Data Store. This is a layer of code that reads and writes the session data to a particular storage medium. ASP.NET 2.0 allows the developer specify his data store. The session data store class inherits fom the SessionStateStoreProviderBase class. It has a number of methods that can be manipulated.

The BeginRequest is fired when the session begins and is called by default by the AcquireRequestState event.

The CreateNewStoreData creates a new object to contain all the state information specific to a session. It returns an object of the type SessionStateStoreData.

Dispose releases all the resources used by the session data store object.

EndRequest is called by default to end a session state module.

GetItem gets the session data from the data store. It serves requests from applications that use read only session state.

GetItemExclusive gets the session data from the data store and locks it for any request that has readwrite privilege.

Init receives the object packed with the configuration settings for a custom session state and initializes the provider class.

ReleaseItemExclusive unlocks the session state item by a call to the GetExclusive method. RemoveItem removes the session data store item from the session data store.

ResetItemTimeout resets the expiry time of a session state object based on the session’s timeout value.

SetAndReleaseItemExclusive writes a session data item to a data store.

SetItemExpireCallback calls this method to notify the data store class that the caller has registered a Session_OnEnd handler.

The sessionState configuration section can be modified to take advantage of the custom session data providers. The code would look as under:

< sessionState mode=”custom”
CustomType=”Samples.MyDataStore.MyDataStoreLib” >
.
.
.
< / sessionState >

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