Two of the new classes inside of System.NET.Cache are the HTTPRequestCachePolicy and RequestCachePolicy. It gives us some control on client side caching on a request by request basis. Since I think “web apps” when I think about caching, it took me some time to grok (with some help from a few folks at MS) what it’s real purpose is.

Of course, it doesn’t make sense that a webserver based app would have ultimate control over client side caching (wouldn’t that be cool though – magic, but cool!) As far as I know, only the client machine has knowledge of what is in its’ cache.

These classes are available for client and middle tier applications that are making HTTPWebRequests or FTPWebRequests and allow you to control how a webrequest is handled based on either the age of what is available in the cache or just by the location.

Since I do most of my interaction with a webserver via web services* or aspx pages, this doesn’t solve any problems that I am currently having, but it has given me some ideas of how I might leverage it in my applications.

Here are some ideas.

Say you have a web application that creates a pdf report and returns it to the calling client – maybe that is a windows app or even a web app that is the client. The data for this report does not change very much during the course of the day and it is a huge report. So you don’t realy want users taxing the webserver by requesting it more than once per day. You can tell the calling application to first check the local cache and if that download is in there and it is less than one day old, then it will not bother making the request.

Another example is for windows apps that actually use the web browser control. I have never had occasion to do this myself. But you can control how calls are made to the webserver to populate that control with instructions similar to the above sample – based on age or freshness – or you can instruct it to always go from the local cache under certain situations or always from the server. Or you can tell it that if there is nothing in the cache than get it from the server, but otherwise always get it from the cache. My simple demo on this only showed interaction with this funcationality. I had a web page that displayed the current time and you could see, for example, the time not changing for 5 seconds even though I was doing rapid-fire refreshes on the page.

This is not earth shattering functionality for the work that I do, but I can imagine that people writing applications for large corporations would benefit greatly from every tool that reduces the toll on the webserver. You can read more in this online documentation for .NET 2.0: Cache Management for Network Applications.

*re: web services – I REALLY wanted this to work with web services, but it just doesn’t. Although you can pass it the uri of an asmx file, there is no way to call the web method. I tried setting up the definition of the policy against the entire web service and then making a call to the webmethod, but it just didn’t work.

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