static Map<Class<?>, SelfContainedPluginRegistry> generateRegistries(
            final EmbulkSystemProperties embulkSystemProperties,
            final PluginClassLoaderFactory pluginClassLoaderFactory) {
        final HashMap<Class<?>, SelfContainedPluginRegistry> registries = new HashMap<>();
        for (final Map.Entry<Class<?>, String> entry : CATEGORIES.entrySet()) {
            registries.put(
                    entry.getKey(),
                    new SelfContainedPluginRegistry(entry.getKey(), entry.getValue(), embulkSystemProperties, pluginClassLoaderFactory));
        }
        return Collections.unmodifiableMap(registries);
    }
Caches self-contained plugin's loaded classes such as embulk-ruby's Embulk::PluginRegistry.

<p>See {@code /embulk-ruby/lib/embulk/plugin_registry.rb}.
embulk-core/src/main/java/org/embulk/plugin/SelfContainedPluginRegistry.java