presto-main/src/main/java/io/prestosql/server/PluginManager.java/PluginManager/buildClassLoader
class PluginManager:    private PluginClassLoader buildClassLoader(String plugin)
            throws Exception
    {
        File file = new File(plugin);
        if (file.isFile() && (file.getName().equals("pom.xml") || file.getName().endsWith(".pom"))) {
            return buildClassLoaderFromPom(file);
        }
        if (file.isDirectory()) {
            return buildClassLoaderFromDirectory(file);
        }
        return buildClassLoaderFromCoordinates(plugin);
    }