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    file to identify the same message.</p>

<p>For example, you might prepare files in French, Spanish, and English that
    contain language-specific versions of the word "Hello". The French file
    would
    be named <code>Messages_fr.properties</code> and contain the following:
</p>
<pre>
    hi=Bonjour
</pre>

<p>while the Spanish and English files would be named
    <code>Messages_es.properties</code> and <code>
    Messages_en.properties</code>
    respectively. The corresponding message string definitions would say
    <code>hi=Hola</code> and <code>hi=Hello</code> in these files.</p>

<p>Second, place these properties files into the class path for your
    application, exactly as you would with class files themselves. The name
    actually used to load resources will look like a fully qualified Java
    class
    name (with appropriate package prefixes), so the file should be nested
    inside
    a directory structure that matches the packaging (either in an unpacked
    directory, or within a JAR file, as appropriate). For example, assume you
    place directory "foo" on your classpath, and stored the above properties
    files
    in directory "foo/com/mycompany/mypackage". (If you were using a JAR file
    like
    "foo.jar" instead, the files would be in directory
    "com/mycompany/mypackage"
    within the JAR file).

<p>Third, initialize a <code>MessageResources</code> object that corresponds
    to the set of properties files for a particular name, within a particular
    package. The easiest way to do this is to initialize a variable in your
    main
    application class, like this:</p>
<pre>
    public static MessageResources messages =
    MessageResources.getMessageResources("com.mycompany.mypackage.Messages");
</pre>

<p>Note that the "com.mycompany.mypackage" part of the name matches the
    package
    directory into which you placed your properties files, and "Messages" is
    the
    filename prefix for the particular family of properties files supported by
    this
    <code>MessageResources</code> instance. Depending on your development
    process,
    you might find it convenient to store all message strings for an entire
    application in a single properties file family, or to have several
    families -
    in Struts, for example, there is a family of properties files for each
    Java
    package.</p>

<p>To access a message string with a particular Locale, execute a statement
    like this:</p>
<pre>
    Locale locale = ... select the locale to be used ...
    String message = messages.getMessage(locale, "hi");
</pre>

<p>In this case, the variable <code>message</code> will contain the message
    string corresponding to the key "hi", in the language that corresponds to
    the
    locale that was selected.</p>

<p>For an example of message formatting with replaceable parameters, assume
    that the message strings looked like this, instead (only the English
    version
    is shown - corresponding changes would be made in the other files):</p>
<pre>
    hi=Hello {0}
</pre>

<p>Now, you can personalize the retrieved message like this:</p>
<pre>
    Locale locale = ... select the locale to be used ...
    String name = "Joe";
    String message = messages.getMessage(locale, "hi", name);
</pre>

<p>and the marker "{0}" will have been replaced by the specified name (Joe),
    no matter which language is in use. See the JavaDoc API documentation for
    the
    <code>java.text.MessageFormat</code> class for more advanced uses of the
    parameter replacement mechanism.</p>

<h5>Developing Your Own MessageResources Implementation</h5>

<p>In the above example, we were using the default
    <code>MessageResources</code> implementation supplied by Struts, which
    uses
    property files to store the message strings. It is also possible to create
    customized mechanisms to retrieve messages (such as loading them on demand
    from a database). The steps required are as follows:</p>
<ul>
    <li>Create a customized subclass of
        <code>org.apache.struts.util.MessageResources</code> that implements
        message lookup operations as you require.</li>
    <li>Create a customized subclass of
        <code>org.apache.struts.util.MessageResourcesFactory</code> that will
        create an instance of your custom <code>MessageResources</code> class
        when the <code>createResources</code> method is called. Note that the
        "config" argument to this method can be used to select families of
        messages in any manner appropriate to your needs - you are not
        required
        to emulate the "fully qualified Java class name" approach that is used
        by the standard <code>PropertyMessageResourcesFactory</code> class.
    </li>
    <li>Tell the <code>MessageResourcesFactory</code> class the name of the
        customized <code>MessageResourcesFactory</code> implementation to use
        when creating new factory instances.</li>
    <li>Create a new factory instance.</li>
    <li>Ask the new factory instance to create a <code>MessageResources</code>
        instance for you.</li>
</ul>

<p>A code example that illustrates this technique is:</p>
<pre>
    MessageResourcesFactory.setFactoryClass("com.mycompany.mypkg.MyFactory");
    MessageResourcesFactory factory = MessageResourcesFactory.createFactory();
    MessageResources resources =
    factory.createResources("configuration information");
</pre>

<p>Once you have created your custom MessageResources instance, you utilize it
    to access message strings (with or without parameter replacement objects),
    exactly as we illustrated with the standard implementation in the previous
    section.</p>

<h5>Using MessageResources With Struts</h5>

<p>If your application uses the Struts controller servlet, you can optionally
    configure Struts to load an application-specific message resources
    instance for
    you, and make it available as a servlet context attribute (in JSP terms,
    an
    application-scope bean). This mechanism is managed by setting the
    following
    servlet initialization parameters in the web application deployment
    descriptor:
</p>
<ul>
    <li><strong>application</strong> - The configuration string that will be
        passed to the <code>createResources()</code> method of the message
        resources factory, in order to identify the family of resources to be
        supported. If you use the standard message resources factory, this
        must
        be the base fully qualified name of the property resources files used
        to contain these messages, as illustrated above.</li>
    <li><strong>factory</strong> - Fully qualified Java class name of the
        <code>MessageResourcesFactory</code> to be used. By default, the
        standard
        implementation provided by Struts
        (<code>org.apache.struts.util.PropertyMessageResourcesFactory</code>)
        will be used.</li>
</ul>

<p>Struts provides several JSP custom tags that assume the existence of a
    <code>java.util.Locale</code> attribute in the user's session, under the
    key
    named by the constant string value of <code>Action.LOCALE_KEY</code>. Your
    own
    application logic can set this attribute at any time, or you can ask
    Struts to
    set it automatically (if not already set) based on the
    <code>Accept-Language</code> HTTP header included with the request. There
    are
    two mechanisms by which you request Struts to perform this service:</p>
<ul>
    <li>To have this service performed on every request submitted to the
        controller
        servlet, set the servlet initialization parameter <code>locale</code>
        to
        the value <code>true</code> in the application deployment descriptor.
    </li>
    <li>To have this service performed by a JSP page when it is accessed
        directly
        by a user, utilize a <code>&lt;form:html ... locale="true" ...
        /&gt;</code>
        tag at the top of each page.</li>
</ul>

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