The more meaningful and short a URL can be, the better. Those URLs are easier to communicate to people, and easier for them to remember. The current URLs that allow us to browse articles for a specific category are already pretty short, but it’s not easy to remember all category IDs by heart . . . and thus to remember the URL. ASP.NET 2.0 introduces a new section in web.config that allows us to map a virtual URL to a real URL: This section’s name is urlMapping, and it’s located under <system.web>. When the user types the virtual URL, the page located at the corresponding real URL will be loaded. Here’s what you can write in web.config to make your sample categories easier to reach:

<urlMappings>

   <add url="~/articles/beer.aspx" mappedUrl="~/BrowseArticles.aspx?CatID=28" />

   <add url="~/articles/events.aspx" mappedUrl="~/BrowseArticles.aspx?CatID=41" />

   <add url="~/articles/news.aspx" mappedUrl="~/BrowseArticles.aspx?CatID=31" />

   <add url="~/articles/photos.aspx" mappedUrl="~/BrowseArticles.aspx?CatID=40" />

   <add url="~/articles/blog.aspx" mappedUrl="~/BrowseArticles.aspx?CatID=29" />

   <add url="~/articles/faq.aspx" mappedUrl="~/BrowseArticles.aspx?CatID=42" />

</urlMappings>

Note that when the server receives a request for the virtual URL it doesn’t make a normal redirect to the real URL. Before the page is loaded, ASP.NET rewrites the URL to the request’s context. From that point on, the URL will be read from the context, and thus the correct URL will be retrieved. The bottom line is that the transition is done in memory on the server side, and users do not even see the real URL in their browser. Therefore, if a user maneuvers to ~/articles/beer.aspx she’s really going to get ~/BrowseArticles.aspx?CatID=28. Furthermore, there is no physical page named ~/articles/beer.aspx.

This could have been done in ASP.NET 1.1, but you had to write your own custom HTTP module to do that, from which you would have used the current HttpContext’s RewritePath method to do the in-memory redirect.