private static Class loadSelfContainedJarPluginMainClass(final String selfContainedPluginName,
                                                             final String pluginMainClassName,
                                                             final PluginClassLoaderFactory pluginClassLoaderFactory)
            throws InvalidJarPluginException {
        final PluginClassLoader pluginClassLoader = pluginClassLoaderFactory.forSelfContainedPlugin(
                selfContainedPluginName, JarPluginLoader.class.getClassLoader());

        final Class pluginMainClass;
        try {
            pluginMainClass = pluginClassLoader.loadClass(pluginMainClassName);
        } catch (ClassNotFoundException ex) {
            throw new InvalidJarPluginException("Class " + pluginMainClassName + " not found in " + selfContainedPluginName,
                                                ex);
        }

        return pluginMainClass;
    }
Opens JarURLConnection for the given JAR file path.

Note that JarURLConnection does not have {@code disconnect} nor {@code close}.
embulk-core/src/main/java/org/embulk/plugin/jar/JarPluginLoader.java