ReDJ is a Joomla native extension that allows to efficiently manage URL redirection. This is very useful for creating URL aliases, and managing redirects from an old URL to a new one. A very similar extension has been added into Joomla since version 1.6, but ReDJ supports powerful regular expressions that allow to match more than one source URL. In this way it is possible to create a group of redirects with just one ReDJ rule.

ReDJ also supports usage of "macros" in the destination URL. A macro is like a function whose value is calculated at runtime (when the rule matches an URL). There are a loto of macros available and this allows to create dynamic destinations, with a different redirection for each source URL. To increase flexibilty in the building of dynamic destinations, also "placeholders" are supported. A placeholder is like a variable whose value can be assigned using text, macros or other placeholders, and can be used to build the destination.

Another great ReDJ feature is the configurable redirection type for each item, with support for 301 (Moved Permanently), 307 (Temporary Redirect) and also 200 (Internal Redirect) (available for Enterprise version only). With the Internal Redirect is now possible to create a "real" URL alias with Joomla.

Last but not least, there are many other features available, such custom error pages, error tracing, referer tracing and so on, that can dramatically improve your SEO ranking. We will describe each one in detail in the next part of this guide. In the following paragraphs we will also learn how to make better use of regular expressions, macros and placeholders to take full advantage from ReDJ.

How it works

ReDJ package includes a component for managing list of redirection rules, and a plugin that examines all the requests and redirect them to a different page when needed by an active rule. These are the main steps to start using ReDJ (for the impatient):

1. Install the package using Joomla Administration interface;
2. Enable the plugin "System - ReDJ" and set its ordering and other parameters;
3. Use ReDJ component to manage redirects, errors and referers.

Detailed instructions on each step are described in the following paragraphs. In this section we just want to focus on some basic concepts related to ReDJ and how it works.

The first important thing to understand is the "rule" concept. With ReDJ Manager (the component interface) you can create as many items as you want, and each item is a redirection rule. But not necessarily an item corresponds to a single page (i.e. matches just a single URL).

A rule has a "From URL" field that can be full URI or just a part of it. For example, it can be "/home.html", then this rule matches both the URL http://www.mysite.com/home.html and http://www.mysite.com/orders/home.html?view=status. So, it means that with a single rule is possible to match multiple source URLs. But the content of the "From URL" field can be a regular expression, and this provide a powerful way to specify complex search patterns for matching URL. The "Skip" field is similar to From URL", it can be a part of URL and contains a regular expression, but it offers a way to skip the rule. When the skip condition matches the rule is discarded. In the next paragraphs will be shown many regular expression examples.

For any request on the site, the ReDJ plugin compares the requested URL with all the rules enabled in the ordering set for rules. The first matching rule found (if there's at least one) is used for redirect.