HttpContext with example

HttpContext.Current is available to all pages, but not necessarily to all threads. If you try to use it inside a background thread, ThreadPool delegate, async call (using an ASP.NET Async page), etc., you'll end up with a NullReferenceException.

If you need to get access to the cache from library classes, i.e. classes that don't have knowledge of the current request, you should use HttpRuntime.Cache instead. This is more reliable because it doesn't depend on an HttpContext.

To ADD in to cache.

HttpContext.Current.Cache.Add("hi", x, null, DateTime.MaxValue,
                               Cache.NoSlidingExpiration,
                               CacheItemPriority.Normal, null);

Retrieve from cache.

HttpRuntime.Cache[key]

please refer,

http://msdn.microsoft.com/en-us/library/system.web.httpcontext.cache.aspx

http://weblogs.asp.net/pjohnson/archive/2006/02/06/httpruntime-cache-vs-httpcontext-current-cache.aspx

hope this help.