Session

A session is defined as the period of time that a unique user interacts with a Web application. Programmatically, session state is nothing more than memory in the shape of a dictionary or hash table, e.g. key-value pairs, which can be set and read for the duration of a user's session. Features of ASP.Net Session State 1. Process independent. ASP.NET session state is able to run in a separate process from the ASP.NET host process. If session state is in a separate process, the ASP.NET process can come and go while the session state process remains available. Of course, you can still use session state in process similar to classic ASP, too. 2. Support for server farm configurations. By moving to an out-of-process model, ASP.NET also solves the server farm problem. The new out-of-process model allows all servers in the farm to share a session state process. You can implement this by changing the ASP.NET configuration to point to a common server. 3. Cookie independent. Although solutions to the problem of cookieless state management do exist for classic ASP, they're not trivial to implement. ASP.NET, on the other hand, reduces the complexities of cookieless session state to a simple configuration setting. Session configuration Below is a sample config.web file used to configure the session state settings for an ASP.NET application: <sessionstate mode="inproc" cookieless="false" timeout="20" sqlconnectionstring="data source=127.0.0.1;user id=<user id>;password=<password>" server="127.0.0.1" port="42424" /> The settings above are used to configure ASP.NET session state. Let's look at each in more detail and cover the various uses afterward.

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Attribut e

Mode. The mode setting supports three options: inproc, sqlserver, and stateserver. As stated earlier, ASP.NET supports two modes: in process and out of process. There are also two options for out-of-process state management: memory based (stateserver), and SQL Server based (sqlserver). We'll discuss implementing these options shortly. Cookieless. The cookieless option for ASP.NET is configured with this simple Boolean setting. Timeout. This option controls the length of time a session is considered valid. The session timeout is a sliding value; on each request the timeout period is set to the current time plus the timeout value Sqlconnectionstring. The sqlconnectionstring identifies the database connection string that names the database used for mode sqlserver. Server. In the out-of-process mode stateserver, it names the server that is running the required Windows NT service: ASPState. Port. The port setting, which accompanies the server setting, identifies the port number that corresponds to the server setting for mode stateserver.

Option

mode

Description Specifies where to store the session state.

Off

Disables session state management.

InProc

Session state is stored locally in memory of ASP.NET worker process.

StateServ Session state is stored outside ASP.NET worker process and is managed by Windows er service. Location of this service is specified by stateConnectionString attribute. SQLServer

Session state is stored outside ASP.NET worker process in SQL Server database. Location of this database is represented by sqlConnectionString attribute.

State Management in ASP.NET Web form pages are HTTP-Based, they are stateless, which means they don’t know whether the

requests are all from the same client, and pages are destroyed and recreated with each round trip to the server, therefore information will be lost, therefore state management is really an issue in developing web applications We could easily solve these problems in ASP with cookie, query string, application, session and so on. Now in ASP.NET, we still can use these functions, but they are richer and more powerful, so let’s dive into it.Mainly there are two different ways to manage web page’s state: Client-side and Server-side. 1.Client-side state management :There is no information maintained on the server between round trips. Information will be stored in the page or on the client’s computer. A. Cookies. A cookie is a small amount of data stored either in a text file on the client's file system or in-memory in the client browser session. Cookies are mainly used for tracking data settings. Let’s take an example: say we want to customize a welcome web page, when the user request the default web page, the application first to detect if the user has logined before, we can retrieve the user informatin from cookies: [c#] if (Request.Cookies[“username”]!=null) lbMessage.text=”Dear “+Request.Cookies[“username”].Value+”, Welcome shopping here!”; else lbMessage.text=”Welcome shopping here!”; If you want to store client’s information, you can use the following code: [c#] Response.Cookies[“username’].Value=username; So next time when the user request the web page, you can easily recongnize the user again. B. Hidden Field A hidden field does not render visibly in the browser, but you can set its properties just as you can with a standard control. When a page is submitted to the server, the content of a hidden field is sent in the HTTP Form collection along with the values of other controls. A hidden field acts as a repository for any pagespecific information that you would like to store directly in the page. Hidden field stores a single variable in its value property and must be explicitly added it to the page. ASP.NET provides the HtmlInputHidden control that offers hidden field functionality. [c#] protected System.Web.UI.HtmlControls.HtmlInputHidden Hidden1; //to assign a value to Hidden field Hidden1.Value=”this is a test”; //to retrieve a value string str=Hidden1.Value; Note: Keep in mind, in order to use hidden field, you have to use HTTP-Post method to post web page. Although its name is ‘Hidden’, its value is not hidden, you can see its value through ‘view source’ function. C. View State Each control on a Web Forms page, including the page itself, has a ViewState property, it is a built-in struture for automatic retention of page and control state, which means you don’t need to do anything about getting back the data of controls after posting page to the server. Here, which is useful to us is the ViewState property, we can use it to save information between round trips to the server. [c#] //to save information ViewState.Add(“shape”,”circle”); //to retrieve information string shapes=ViewState[“shape”]; Note: Unlike Hidden Field, the values in ViewState are invisible when ‘view source’, they are compressed and encoded.

D. Query Strings Query strings provide a simple but limited way of maintaining some state information.You can easily pass information from one page to another, But most browsers and client devices impose a 255-character limit on the length of the URL. In addition, the query values are exposed to the Internet via the URL so in some

cases security may be an issue. A URL with query strings may look like this: http://www.examples.com/list.aspx?categoryid=1&productid=101 When list.aspx is being requested, the category and product information can be obtained by using the following codes: [c#] string categoryid, productid; categoryid=Request.Params[“categoryid”]; productid=Request.Params[“productid”]; Note: you can only use HTTP-Get method to post the web page, or you will never get the value from query strings. 2. Server-side state management: Information will be stored on the server, it has higher security but it can use more web server resources. A. Aplication object The Application object provides a mechanism for storing data that is accessible to all code running within the Web application, The ideal data to insert into application state variables is data that is shared by multiple sessions and does not change often.. And just because it is visible to the entire application, you need to used Lock and UnLock pair to avoid having conflit value. [c#] Application.Lock(); Application[“mydata”]=”mydata”; Application.UnLock(); B. Session object Session object can be used for storing session-specific information that needs to be maintained between server round trips and between requests for pages. Session object is per-client basis, which means different clients generate different session object.The ideal data to store in session-state variables is shortlived, sensitive data that is specific to an individual session. Each active ASP.NET session is identified and tracked using a 120-bit SessionID string containing URLlegal ASCII characters. SessionID values are generated using an algorithm that guarantees uniqueness so that sessions do not collide, and SessionID’s randomness makes it harder to guess the session ID of an existing session. SessionIDs are communicated across client-server requests either by an HTTP cookie or a modified URL, depending on how you set the application's configuration settings. So how to set the session setting in application configuration? Ok, let’s go further to look at it. Every web application must have a configuration file named web.config, it is a XML-Based file, there is a section name ‘sessionState’, the following is an example: <sessionState mode="InProc" stateConnectionString="tcpip=127.0.0.1:42424" sqlConnectionString="data source=127.0.0.1;user id=sa;password=" cookieless="false" timeout="20" /> ‘cookieless’ option can be ‘true’ or ‘false’. When it is ‘false’(default value), ASP.NET will use HTTP cookie to identify users. When it is ‘true’, ASP.NET will randomly generate a unique number and put it just right ahead of the requested file, this number is used to identify users, you can see it on the address bar of IE: http://localhost/Management/(2yzakzez3eqxut45ukyzq3qp)/Default.aspx Ok, it is further enough, let is go back to session object. [c#] //to store information Session[“myname”]=”Mike”; //to retrieve information myname=Session[“myname”]; C. Database Database enables you to store large amount of information pertaining to state in your Web application. Sometimes users continually query the database by using the unique ID, you can save it in the database

for use across multiple request for the pages in your site.

Summary ASP.NET has more functions and utilities than ASP to enable you to manage page state more efficient and effective. Choosing among the options will depand upon your application, you have to think about the following before making any choose:

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How much information do you need to store? Does the client accept persistent or in-memory cookies? Do you want to store the information on the client or server? Is the information sensitive? What kind of performance experience are you expecting from your pages?

Client-side state management summary Method

Use when

Cookies

You need to store small amounts of information on the client and security is not an issue.

View state

You need to store small amounts of information for a page that will post back to itself. Use of the ViewState property does supply semi-secure functionality.

Hidden fields

You need to store small amounts of information for a page that will post back to itself or another page, and security is not an issue. Note You can use a hidden field only on pages that are submitted to the server.

Query string

You are transferring small amounts of information from one page to another and security is not an issue. Note You can use query strings only if you are requesting the same page, or another page via a link.

Server-side state management summary Method Use when Application state object You are storing infrequently changed, application-scope information that is used by many users, and security is not an issue. Do not store large quantities of information in an application state object. Session state object You are storing short-lived information that is specific to an individual session, and security is an issue. Do not store large quantities of information in a session state object. Be aware that a session state object will be created and maintained for the lifetime of every session in your application. In applications hosting many users, this can occupy significant server resources and affect scalability. Database support You are storing large amounts of information, managing transactions, or the information must survive application and session restarts. Data mining is a concern, and security is an issue. ASP.NET Caching Features When clients access an ASP.NET page, there are basically two ways to provide them with the information they need:

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the ASP.NET page can either obtain information from server resources, such as from data that has been persisted to a database, or the ASP.NET page can obtain information from within the application.

Retrieving information from a resource outside the application will require more processing steps, and will therefore require more time and resources on the server than if the information can be obtained from within the application space. If the information that will be sent to the browser has already been prepared by a previous request, the application will be able to retrieve that information faster if it has been stored in memory, somewhere along the request/response stream. Known as caching, this technique can be used to temporarily store page output or application data either on the client or on the server, which can then be re-used to satisfy subsequent requests and thus avoid the overhead of re-creating the same information.

Caching is particularly suitable when you expect to return the same information in the same format for many different requests. ASP.NET provides the following types of caching that can be used to build highly responsive Web applications:

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Output caching, which caches the dynamic response generated by a request. Fragment caching, which caches portions of a response generated by a request. Data caching, which allows developers to programmatically retain arbitrary data across requests.