public static JsonParser createJsonParser(InputStream inputStream) throws XmlUtilException {
        if ( jsonFactory == null ) {
            synchronized ( LOCK_OBJECT ) {
                if ( jsonFactory == null ) {
                    jsonFactory = new JsonFactory();
                }
            }
        }

        try {
            return jsonFactory.createJsonParser(inputStream);
        } catch (IOException e) {
            throw new XmlUtilException("JSONパーサの生成に失敗しました。", e);
        }
    }