Application Configuration Resource File
JavaServer Faces technology provides a portable configuration format (as an XML document) for configuring application resources. One or more XML documents, called application configuration resource files, may use this format to register and configure objects and resources, and to define navigation rules for applications. An application configuration resource file is usually named faces-config.xml.
You need an application configuration resource file in the following cases:
To specify configuration elements for your application that are not available through managed bean annotations, such as localized messages and navigation rules
To override managed bean annotations when the application is deployed
The application configuration resource file must be valid against the XML schema located at http://java.sun.com/xml/ns/javaee/web-facesconfig_2_0.xsd.
In addition, each file must include the following information, in the following order:
The XML version number, usually with an encoding attribute:
<?xml version="1.0" encoding='UTF-8'?>
A faces-config tag enclosing all the other declarations:
<faces-config version="2.0" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-facesconfig_2_0.xsd"> ... </faces-config>
You can have more than one application configuration resource file for an application. The JavaServer Faces implementation finds the configuration file or files by looking for the following:
A resource named /META-INF/faces-config.xml in any of the JAR files in the web application’s /WEB-INF/lib/ directory and in parent class loaders. If a resource with this name exists, it is loaded as a configuration resource. This method is practical for a packaged library containing some components and renderers. In addition, any file with a name that ends in faces-config.xml is also considered a configuration resource and is loaded as such.
A context initialization parameter, javax.faces.application.CONFIG_FILES, in your web deployment descriptor file that specifies one or more (comma-delimited) paths to multiple configuration files for your web application. This method is most often used for enterprise-scale applications that delegate to separate groups the responsibility for maintaining the file for each portion of a big application.
A resource named faces-config.xml in the /WEB-INF/ directory of your application. Simple web applications make their configuration files available in this way.
To access the resources registered with the application, an application developer can use an instance of the javax.faces.application.Application class, which is automatically created for each application. The Application instance acts as a centralized factory for resources that are defined in the XML file.
When an application starts up, the JavaServer Faces implementation creates a single instance of the Application class and configures it with the information you provided in the application configuration resource file.
Ordering of Application Configuration Resource Files
Because JavaServer Faces technology allows the use of multiple application configuration resource files stored in different locations, the order in which they are loaded by the implementation becomes important in certain situations (for example, when using application-level objects). This order can be defined through an ordering element and its subelements in the application configuration resource file itself. The ordering of application configuration resource files can be absolute or relative.
Absolute ordering is defined by an absolute-ordering element in the file. With absolute ordering, the user specifies the order in which application configuration resource files will be loaded. The following example shows an entry for absolute ordering:
<faces-config> <name>myJSF</name> <absolute-ordering> <name>A</name> <name>B</name> <name>C</name> </absolute-ordering> </faces-config>
In this example, A, B, and C are different application configuration resource files and are to be loaded in the listed order.
If there is an absolute-ordering element in the file, only the files listed by the subelement name are processed. To process any other application configuration resource files, an others subelement is required. In the absence of the others subelement, all other unlisted files will be ignored at load time.
Relative ordering is defined by an ordering element and its subelements before and after. With relative ordering, the order in which application configuration resource files will be loaded is calculated by considering ordering entries from the different files. The following example shows some of these considerations. In the following example, config-A, config-B, and config-C are different application configuration resource files.
File config-A contains the following elements:
<faces-config> <name>config-A</name> <ordering> <before> <name>config-B</name> </before> </ordering> </faces-config>
File config-B (not shown here) does not contain any ordering elements.
File config-C contains the following elements:
<faces-config> <name>config-C</name> <ordering> <after> <name>config-B</name> </after> </ordering> </faces-config>
Based on the before subelement entry, file config-A will be loaded before the config-B file. Based on the after subelement entry, file config-C will be loaded after the config-B file.
In addition, a subelement others can also be nested within the before and after subelements. If the others element is present, the specified file may receive highest or lowest preference among both listed and unlisted configuration files.
If an ordering element is not present in an application configuration file, then that file will be loaded after all the files that contain ordering elements.