public static String toString(final byte[] bytes) {
        if (bytes == null) {
            return null;
        }
        return toString(bytes, 0, bytes.length);
    }
copy google protocol buffer
https://github.com/google/protobuf/blob/master/java/src/main/java/com/google/protobuf/CodedOutputStream.java
commons/src/main/java/com/navercorp/pinpoint/common/util/BytesUtils.java