private static void initializeAll(final HashMap<String, ArrayList<String>> jarFileResources) {
        synchronized (JAR_RESOURCE_NAMES) {
            if (JAR_RESOURCE_NAMES.isEmpty()) {
                for (final Map.Entry<String, ArrayList<String>> entry : jarFileResources.entrySet()) {
                    JAR_RESOURCE_NAMES.put(entry.getKey(), entry.getValue());
                }
            } else {
                throw new LinkageError("Double initialization of self-contained JAR files.");
            }
        }
    }
It must be called initially at once before all other getResource*() methods are called.

public to be called from org.embulk.cli. Not for plugins. Not guaranteed.
embulk-core/src/main/java/org/embulk/cli/SelfContainedJarFiles.java