Download the YUI Compressor JAR

The YUI Compressor is written in Java and distributed as a JAR. Download the JAR from the Yahoo! site and save it to app/Resources/java/yuicompressor.jar.

Configure the YUI Filters

Now you need to configure two Assetic filters in your application, one for minifying JavaScripts with the YUI Compressor and one for minifying stylesheets:

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# app/config/config.yml
assetic:
    # java: "/usr/bin/java"
    filters:
        yui_css:
            jar: "%kernel.root_dir%/Resources/java/yuicompressor.jar"
        yui_js:
            jar: "%kernel.root_dir%/Resources/java/yuicompressor.jar"

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<!-- app/config/config.xml -->
<assetic:config>
    <assetic:filter
        name="yui_css"
        jar="%kernel.root_dir%/Resources/java/yuicompressor.jar" />
    <assetic:filter
        name="yui_js"
        jar="%kernel.root_dir%/Resources/java/yuicompressor.jar" />
</assetic:config>

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// app/config/config.php
$container->loadFromExtension('assetic', array(
    // 'java' => '/usr/bin/java',
    'filters' => array(
        'yui_css' => array(
            'jar' => '%kernel.root_dir%/Resources/java/yuicompressor.jar',
        ),
        'yui_js' => array(
            'jar' => '%kernel.root_dir%/Resources/java/yuicompressor.jar',
        ),
    ),
));

You now have access to two new Assetic filters in your application: yui_css and yui_js. These will use the YUI Compressor to minify stylesheets and JavaScripts, respectively.

Minify your Assets

You have YUI Compressor configured now, but nothing is going to happen until you apply one of these filters to an asset. Since your assets are a part of the view layer, this work is done in your templates:

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{% javascripts '@AcmeFooBundle/Resources/public/js/*' filter='yui_js' %}
    <script src="{{ asset_url }}"></script>
{% endjavascripts %}

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<?php foreach ($view['assetic']->javascripts(
    array('@AcmeFooBundle/Resources/public/js/*'),
    array('yui_js')
) as $url): ?>
    <script src="<?php echo $view->escape($url) ?>"></script>
<?php endforeach; ?>

With the addition of the yui_js filter to the asset tags above, you should now see minified JavaScripts coming over the wire much faster. The same process can be repeated to minify your stylesheets.

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{% stylesheets '@AcmeFooBundle/Resources/public/css/*' filter='yui_css' %}
    <link rel="stylesheet" type="text/css" media="screen" href="{{ asset_url }}" />
{% endstylesheets %}

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<?php foreach ($view['assetic']->stylesheets(
    array('@AcmeFooBundle/Resources/public/css/*'),
    array('yui_css')
) as $url): ?>
    <link rel="stylesheet" type="text/css" media="screen" href="<?php echo $view->escape($url) ?>" />
<?php endforeach; ?>

Disable Minification in Debug Mode

Minified JavaScripts and Stylesheets are very difficult to read, let alone debug. Because of this, Assetic lets you disable a certain filter when your application is in debug mode. You can do this by prefixing the filter name in your template with a question mark: ?. This tells Assetic to only apply this filter when debug mode is off.

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{% javascripts '@AcmeFooBundle/Resources/public/js/*' filter='?yui_js' %}
    <script src="{{ asset_url }}"></script>
{% endjavascripts %}

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<?php foreach ($view['assetic']->javascripts(
    array('@AcmeFooBundle/Resources/public/js/*'),
    array('?yui_js')
) as $url): ?>
    <script src="<?php echo $view->escape($url) ?>"></script>
<?php endforeach; ?>