presto-main/src/main/java/io/prestosql/server/PluginManager.java/PluginManager/buildClassLoaderFromDirectory
class PluginManager:    private PluginClassLoader buildClassLoaderFromDirectory(File dir)
            throws Exception
    {
        log.info("Classpath for %s:", dir.getName());
        List<URL> urls = new ArrayList<>();
        for (File file : listFiles(dir)) {
            log.info("    %s", file);
            urls.add(file.toURI().toURL());
        }
        return createClassLoader(urls);
    }