public synchronized boolean isExtracted( final String canonicalName )
    {
        return pluginMetadata.containsKey( canonicalName );
    }
Returns true if the plugin by the specified name is extracted. Specifically, this checks if the {@code plugins}
directory contains a subdirectory that matches the canonical name of the plugin.

Note that an <em>installed</em> plugin is not per definition an <em>extracted</em> plugin, and an extracted
plugin is not per definition a <em>loaded</em> plugin.  A plugin that's extracted might, for instance, fail to
load, due to restrictions imposed by its {@code minServerVersion} definition.

@param canonicalName the canonical filename of the plugin (cannot be null).
@return true if the plugin is extracted, otherwise false.
xmppserver/src/main/java/org/jivesoftware/openfire/container/PluginManager.java