You can store one value in a cookie, such as user name or last visit. You can also store multiple name-value pairs in a single cookie. The name-value pairs are referred to as subkeys. For example, instead of creating two separate cookies named userName and lastVisit, you can create a single cookie named userInfo that has the subkeys userName and lastVisit.
You might use subkeys for several reasons. First, it is convenient to put related or similar information into a single cookie. In addition, because all the information is in a single cookie, cookie attributes such as expiration apply to all the information.
A cookie with subkeys also helps you limit the size of cookie files. As noted earlier in the "Cookie Limitations" section, cookies are usually limited to 4096 bytes and you can't store more than 20 cookies per site. By using a single cookie with subkeys, you use fewer of those 20 cookies that your site is allotted. In addition, a single cookie takes up about 50 characters for overhead (expiration information, and so on), plus the length of the value that you store in it, all of which counts toward the 4096-byte limit. If you store five subkeys instead of five separate cookies, you save the overhead of the separate cookies and can save around 200 bytes.
To create a cookie with subkeys, you can use a variation of the syntax for writing a single cookie. The following example shows two ways to write the same cookie, each with two subkeys:
Response.Cookies["userInfo"]["userName"] = "patrick";
Response.Cookies["userInfo"]["lastVisit"] = DateTime.Now.ToString();
Response.Cookies["userInfo"].Expires = DateTime.Now.AddDays(1);
HttpCookie aCookie = new HttpCookie("userInfo");
aCookie.Values["userName"] = "patrick";
aCookie.Values["lastVisit"] = DateTime.Now.ToString();
aCookie.Expires = DateTime.Now.AddDays(1);
Response.Cookies.Add(aCookie);
The browser manages cookies on a user system. Cookies are sent to the browser via the HttpResponse object that exposes a collection called Cookies. You can access the HttpResponse object as the Response property of your Page class. Any cookies that you want to send to the browser must be added to this collection. When creating a cookie, you specify a Name and Value. Each cookie must have a unique name so that it can be identified later when reading it from the browser. Because cookies are stored by name, naming two cookies the same will cause one to be overwritten.
You can also set a cookie's date and time expiration. Expired cookies are deleted by the browser when a user visits the site that wrote the cookies. The expiration of a cookie should be set for as long as your application considers the cookie value to be valid. For a cookie to effectively never expire, you can set the expiration date to be 50 years from now.
Note: Users can clear the cookies on their computer at any time. Utilities such as CCleaner ("crap cleaner") allow you to set the cookies you want to keep, and delete all the rest.
If you do not set the cookie's expiration, the cookie is created but it is not stored on the user's hard disk. Instead, the cookie is maintained in memory as part of the user's session information. When the user closes the browser, the cookie is discarded. A non-persistent cookie like this is useful for information that needs to be stored for only a short time or that for security reasons should not be written to disk on the client computer. For example, non-persistent cookies are useful if the user is working on a public computer, where you do not want to write the cookie to disk.
A query string is information sent to the server appended to the end of a page URL.
Following are the benefits of using query string for state management:-
. No server resources are required. The query string containing in the HTTP requests for a specific URL.
. All browsers support query strings.
Following are limitations of query string:-
. Query string data is directly visible to user thus leading to security problems.-
. Most browsers and client devices impose a 255-character limit on URL length.
Below is a sample "Login" query string passed in URL http://www.jack-fx.com.com/login.asp?login=testing.
This query string data can then be requested later by using Request.QueryString("login").
(I) What is Absolute and Sliding expiration?
Absolute Expiration allows you to specify the duration of the cache, starting from the time the cache is activated. The following example shows that the cache has a cache dependency specified, as well as an expiration time of one minute.
Cache. Insert ("announcement", announcement, depends, _
DateTime.Now.AddMinutes(1), Nothing)
Sliding Expiration specifies that the cache will expire if a request is not made within a specified duration. Sliding expiration policy is useful whenever you have a large number of items that need to be cached, because this policy enables you to keep only the most frequently accessed items in memory. For example, the following code specifies that the cache will have a sliding duration of one minute. If a request is made 59 seconds after the cache is accessed, the validity of the cache would be reset to another minute:
Cache.Insert("announcement", announcement, depends, _
Date Time. Max Value, _
TimeSpan.FromMinutes(1))
