Rewrite engine
A rewrite engine is a piece of web server software used to modify URLs before fetching the requested item, for a variety of purposes. This technique is known as URL rewriting. Some benefits derived from a rewrite engine are:
- Making website URLs more user and search engine friendly
- Preventing undesired "inline linking" or "hot linking"
- Not exposing the (web address-related) inner workings of a website to users
Many of these only apply to HTTP servers whose default behaviour is to map URLs to filesystem entities (i.e. files and directories); certain environments, such as many HTTP application server platforms, make this irrelevant.
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In practice
In Java, the term "URL rewriting" is sometimes used to describe a Web Application Server adding a session id to a URL when cookies are not supported (e.g. "index.jsp" is rewritten to "index.jsp;jsessionid=xyc" when the links are drawn in an HTML page).
Ruby on Rails has built-in URL rewriting via Routes.[1]
Rewrite engines
Apache Software Foundation's Apache HTTP server
- mod_rewrite Apache module described as "the Swiss Army knife of URL manipulation".
- mod_alias Simpler Apache module allow for manipulation and control of URLs as requests arrive at the server..
Microsoft's Internet Information Server (IIS)
- IIS Mod-Rewrite from Micronovae
- IISRewrite from Qwerksoft
- ISAPI_Rewrite from isapirewrite.com
- URL Replacer from Motobit
- Ionic's ISAPI Rewrite Filter (IIRF) (open source) from Ionic Shade.
HttpModule for Microsoft ASP.NET
- UrlRewriter.NET Free, open-source package. Supports .NET 1.1 and 2.0.
- URLRewriting.NET, free and open source supports, ASP.NET 2.0
- VirtualUrl.NET for ASP.NET 2 Professional URL rewriting package.
Java 2 Platform, Enterprise Edition (J2EE) Servlet container servers (such as Apache Tomcat, Resin, Orion etc):
- HttpRedirectFilter (open source)
- UrlRewriteFilter (open source - BSD) - allows you to rewrite URLs before they get to your Sea
User and search engine friendly URLs
People use website URLs in all kinds of ways. They send them to other people by email, put them on online discussion boards, or even write them on scraps of paper. This often applies not just to website home pages, but to specific content within a website. Typically website developers want to encourage this, as it means increased traffic to their sites. As such, a well designed website should allow users to enter at any URL (not just the homepage), and the URLs throughout the site should be easy to use.
A URL is easier to use if it is short but descriptive. The URL should have some text describing the content (not just numbers), but should not be too long.
Search engines will also find it easier to index pages which follow these rules. Content which is easier to index is more likely to be included in search results.
Website URLs are often quite long and quite meaningless to humans. This is because many websites have dynamic content, meaning that HTML returned to the browser is generated on-the-fly, rather than simply being stored as a static HTML file. The URL is used not only to reference an HTML document at a fixed address, but to pass pieces of data to software running on the webserver, which then generates the HTML page dynamically. Typically this software is of the form of scripts written in a web scripting language such as ColdFusion, Perl, PHP, or ASP.
Using a URL rewrite engine, the website software can be presented with URLs in one form, while actual requests (and URLs seen by the user) are in another form. So rewrite engines allow URLs to be tidied up and made more user friendly, by configuring rewrite rules, rather than modifying the webserver software.
See also
External links - Apache
- Free Online Mod Rewrite Tool enabling or disabling Prefixs, Delimiters or Suffix, simple though very powerful online tool.
- Apache's mod_rewrite: a detailed discussion of mod_rewrite's many features.
- Additional Apache URL rewriting guide: more detailed discussion of mod_rewrite
- Using mod_rewrite in a holistic way
- mod_rewrite, a beginner's guide (with examples): a guide to get you started using mod_rewrite.
- Apache mod rewrite tutorials and regular expression lessons: Mod rewrite instruction with Regular Expression syntax lessons, a how to tutorial from beginner to advanced
- Rewrite URLs with mod_rewrite: a tutorial for redirecting URLs.
- The Indie Publisher's mod_rewrite Recipe Book: a collection of mod_rewrite recipes especially for independent publishers.
- URL Rewriting Tool
- Quick introduction to mod_rewrite and when it is useful.
External links - IIS
- 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