Java Platform, Enterprise Edition (Java EE) 8 The Java EE Tutorial

## 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://xmlns.jcp.org/xml/ns/javaee/web-facesconfig_2_2.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="2.2" xmlns="http://xmlns.jcp.org/xml/ns/javaee"
                    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                    http://xmlns.jcp.org/xml/ns/javaee/web-facesconfig_2_2.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.

### Configuring Eager Application-Scoped Managed Beans

JavaServer Faces managed beans (either specified in the f`aces-config.xml` file or annotated with `javax.faces.bean.ManagedBean`) are lazily instantiated. That is, that they are instantiated when a request is made from the application.

To force an application-scoped bean to be instantiated and placed in the application scope as soon as the application is started and before any request is made, the `eager` attribute of the managed bean should be set to `true`, as shown in the following examples.

The `faces-config.xml` file declaration is as follows:

    <managed-bean eager="true">

The annotation is as follows:

    @ManagedBean(eager=true)
    @ApplicationScoped

### 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.

File `my-faces-config.xml` contains the following elements:

    <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.

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