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From Joomla! Documentation
Search engine friendly (SEF), human-readable or clean URLs are URLs that make sense to both humans and search engines because they explain the path to the particular page they point to. Since version 1.5, Joomla! is capable of creating and parsing URLs in any format, including SEF URLs. This does not depend on URL rewriting executed by the web server, so it works even if Joomla! runs a server other than Apache with the mod_rewrite module. The SEF URLs follow a certain fixed pattern, but the user can define a short descriptive text (alias) for each segment of the URL.
Internally, the local part of a SEF URL (the part after the domain name) is called a route. Creating and processing SEF URLs is therefore referred to as routing, and the relevant code is called a router.
A good example of routing is the URL to "Welcome to Joomla!" article in the sample data.
- Without SEF URLs turned on, the URL is
- With SEF URLs on and mod_rewrite off, it's
- With both SEF URLs and mod_rewrite on, it's
Search engine friendly URLs can be activated by turning on the Search Engine Friendly URLs option in the Global Configuration. This option is on by default since Joomla! 1.6. See Enabling Search Engine Friendly (SEF) URLs for more information.
What do the numbers in the URL mean?
By comparing the old and the new URL we can see numbers in the old URL,
but also in the new URL:
These numbers are the parameters that are needed by Joomla! to get the internal URL and show the page you want to see. (In this case, the first numeral one is the ID of the category, the second numeral one is the ID of the article.)
There is no
index.php in the URL anymore. Can I delete the file now?
No! The URL doesn't contain the
index.php anymore, but internally the mod_rewrite will only redirect to the original path without showing it to you.
What is the Alias value? And how does it get created?
Alias is listed beneath the Title field in Articles, Categories, Sections and Menu Items. Joomla! can automatically create the alias for you. An automatic alias begins with the title. All upper case letters are changed to lower case. Spaces and special characters not allowed in a URL; they are changed to dashes.
I want to specify my own value for Alias.
If you do not like the alias provided by Joomla!, you can enter a value of your choosing into that field. Many believe using good keywords in your URL helps search engine optimization. You can do so by including those keywords in your title, and allowing Joomla! to create the alias, or by creating the alias yourself.
How is Alias used in a URL?
For a menu item, Joomla! uses the alias as the URL slug. Assume that you use the first two SEF URL options and you create a menu item called Products. Your URL would be example.com/products.
Joomla! also uses the primary key values of data within the URL to help the router navigate to the correct page. Continuing with the previous example, if your products menu item was for an Article/Category Blog, the link for the Article Title and/or Read More link would have three parts:
- The menu item URL - example.com/products;
- Plus, the primary key for the Category and the Category alias - 32-fruit;
- Plus, the primary key for the Article and the Article alias - 1-apple;
The complete URL is:
How can I get rid of the numbers in the SEF URLs?
The numbers in the SEF URL are needed by Joomla!'s router to know how to direct site traffic. Once the router logic stabilizes, simple third party system plugins can be developed to augment the router capabilities by allowing more choice. At that time, numbers will likely be removed from the URL.
Route Formats and the Routing Mechanism
This section describes Joomla!'s core (built-in) routing mechanism. Routing extensions may change the way routes are created on your system.
To describe the Joomla! routing mechanism in more detail, we first need to pin down what we refer to as a route. Suppose that Joomla! has been installed in
http://example.com/sites/first/. The installation path is generally referred to as the base URL. A possible example URL is
http://example.com/sites/first/products/32-fruit/1-apple. The first part of this URL is the aforementioned base URL, and neither Joomla! nor any component router can create URLs with a different first part. The second part,
products/32-fruit/1-apple, is a route, consisting of three segments.
The first segment of a route is, for regular URLs, the alias of a menu item. The SEF URL is said to be routed through that menu item. The other segments are determined entirely by the router of the component that provides the type of the menu item. The Category - Blog menu item type, for example, is provided by the Content component, and therefore that component's router is responsible for building and parsing the remaining segments.
It is also possible (for extensions) to ask the system to create a route without supplying a menu item to route through. In that case, the system will usually decide to create a special route that has the word
component as the first segment. These routes are created using a fixed format: the name of the component (without the leading
com_) is selected as the second segment and any parameters as the other segments.
It is important to note creating a menu item is the only way for a Joomla! user to define a route that leads to a specific component. It is, however, possible to create a route without showing it on the site (in a menu). An often-applied method is to create a menu item in a menu that isn't displayed anywhere. Such a menu is usually called a hidden menu.
The previous paragraph implies that it is not possible to make one component responsible for handling all routes. For example, it is not possible to specify that the URL
http://example.com/thealias should display the Content item with the alias
thealias could be any word. If this needs to be done for a small number of articles, menu items can be created manually for these. Else a routing extension is necessary.
This routing mechanism is therefore not as flexible as users sometimes require. On the other hand, it has one large advantage: it reduces the chance of ambiguous routes (routes that could lead to two different pages). Since the first segment of a route is always a menu item alias, the system immediately knows which component's router must be used to parse it.
This section describes the routing implementation. If you are a component developer, see Supporting SEF URLs in your component.
Joomla routes are created and resolved by the JRouter class. This class looks in the component root of the currently active component (specified in the
option parameter in the query string) and includes the
router.php file in that component's root directory. It then calls one of two functions: one for creating the SEF URL and one for interpreting the SEF URL.
The JRouter class is overridden by the Joomla CMS in
/includes/router.php. In this file the build and parse functions are overridden to properly build and parse the URLs for the Joomla CMS.
router.php file in each component (for example,
/components/com_content/router.php) should contain the following two functions:
- ContentBuildRoute - this builds the SEF URL
- $query - this is a named array containing the querystring variables
- Returns: an array of segments where each segment is separated by a '/' when later combined to create the actual URL (the items in the array should not contain '/' characters)
- ContentParseRoute - this interprets an SEF URL
- $segments - this is an array that contains the segments of the URL requested.
- Returns: a name => value array of the querystring variables that the link maps to
The SEF Plugin
The Joomla System - SEF plugin inherits
JPlugin and implements the
onAfterRender() function. In this function the body of the response that will be sent to the browser is retrieved using
JResponse::getBody(). The body of the response is then searched for links containing
/index.php... and replaces them with a correct SEF URL by calling
JRoute builds SEF URLs by instantiating a
JRouter object and requesting that it build the correct link from the passed in URL.
Handling SEF URLs
By default the SEF URLs are handled by the
JRouterSite object (from
/includes/router.php) and is called by a call to
JApplication::route() in index.php. This call is made on the
$app variable which is actually an instance of
JApplication::route() has a non-destructive result on the
$_GET array. That is,
JApplication::route() sets variables in
$_GET by calling
JRequest::set() with the overwrite flag set to false. Thus if a variable name is returned from
JRouter::route() that is already in
$_GET, it will not put that value into
$_GET. This allows for custom routing.
Joomla allows you to create your own routing mechanism. In order to create this mechanism you must have a plugin that overrides the
JPlugin::onAfterInitialise() function. This function then parses the URL and creates the needed variables in
$_GET before the standard Joomla routing is done.
See Creating a System Plugin to augment JRouter for an example.