Rewrite engine

A rewrite engine is software that modifies a web URL's appearance (URL rewriting). Rewritten URLs (sometimes known as short or fancy URLs) are used to provide shorter and more relevant-looking links to web pages. The technique adds a degree of separation between the files used to generate a web page and the URL that is presented to the world.

Examples

This URL contains query string parameters that encode blog entry dates

http://www.example.com/Blogs/Posts.php?Year=2006&Month=12&Day=19

but can be altered to give the user a clear idea of what he or she is going to see

 http://www.example.com/Blogs/2006/12/19/ 

The second address also allows the user to change the URL to see all postings available in December, simply by removing the text encoding the day '19', and thereby saving having to navigate the GUI.

http://www.example.com/Blogs/2006/12/

Another example might be changing

http://example.com/wiki/index.php?title=Page_title

to

http://example.com/Page_title 

The benefits of a rewrite engine are:

• Making website URLs more descriptive to improve user-friendliness and search engine optimization
• Preventing undesired "inline linking"
• Not exposing the inner workings of a web site's address to visitors
• The URLs of pages on the web site can be kept even if the underlying technology used to serve them is changed

Known drawbacks:

• In some cases, for example if user modifies URL to get specified data the rewrite engine may hinder from querying. See below example:

Which is a month and which is a day?

http://www.example.com/Blogs/2006/12/10/

In this case, a query that would be more useful is:

http://www.example.com/Blogs/Posts.php?Year=2006&Month=12&Day=10

Modern web frameworks

Recent generations of web frameworks usually include URL rewriting: Ruby on Rails has built-in URL rewriting via Routes, Django uses a regular-expressions based system, Java's Stripes Framework used to require a third-party extension but integrated the module in the core distribution with Stripes 1.5 and the many Perl frameworks have this feature as well.

From a software development perspective, URL rewriting can aid in code modularization and control flow , making it a useful feature of modern web frameworks.

See also

• Permalink
• Apache HTTP Server
• Internet Information Server
• Zeus Web Server
• Content negotiation
• HTTP
• .htaccess

External links

Apache

• mod_rewrite Apache module described as "the Swiss Army knife of URL manipulation".
• Apache Rewrite Guide This document supplements the mod_rewrite reference documentation. It describes how one can use Apache's mod_rewrite to solve typical URL-based problems with which webmasters are commonly confronted.
• mod_alias Simpler Apache module allow for manipulation and control of URLs as requests arrive at the server.

IIS (Microsoft Internet Information Services)

• How to redirect URLs to different Web sites Microsoft Knowledgebase article on built-in URL rewriting
• Scott Guthrie of Microsoft describes various techniques for URL rewriting in .NET
• URL Rewrite Module for IIS 7.0 from Microsoft
• IIS Mod-Rewrite mod_rewrite port for IIS

Zeus Web Server

• Converting Apache rules to ZWS
• Redirecting clients to Alternate Pages
• Zeus Web Server User Guide see page 140 "Configuring Request Rewrite Scripts" (PDF 3.58MB)

Note: Unlike Apache, entering rewrite rules in an .htaccess file will not work. They must be entered in Zeus' proprietary Request Rewrite scripting language through the zeus server's admin panel, which creates a rewrite.script file and installs it into the server. Unless you have access to the main server administration interface, you will need to ask your hosting provider to implement your rule.

Java Platform, Enterprise Edition (Java EE) Servlet container servers (Apache Tomcat, Resin, Orion etc)

• HttpRedirectFilter (open source)
• UrlRewriteFilter (open source - BSD) - allows you to rewrite URLs before they get to your code. Supports XML or mod_rewrite style config.