static Collection<Resource> getMultipleResources(final String targetResourceName, final String category) {
        if (category == null) {
            throw new NullPointerException("SelfContainedJarFiles.getMultipleResources received null.");
        }
        final List<String> jarResourceNames = JAR_RESOURCE_NAMES.get(category);
        if (jarResourceNames == null) {
            throw new IllegalArgumentException(
                    "SelfContainedJarFiles.getMultipleResources received unexpected category: " + category);
        }

        final ArrayList<Resource> resourcesToReturn = new ArrayList<>();
        for (final String jarResourceName : jarResourceNames) {
            final SelfContainedJarFile selfContainedJarFile = Holder.INSTANCE.get(jarResourceName);
            final Resource resourceFound = selfContainedJarFile.getResource(targetResourceName);
            if (resourceFound != null) {
                resourcesToReturn.add(resourceFound);
            }
        }
        return resourcesToReturn;
    }
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