public static byte[] add(final byte[] prefix, final long postfix) {
        if (prefix == null) {
            throw new NullPointerException("prefix");
        }
        byte[] buf = new byte[prefix.length + LONG_BYTE_LENGTH];
        System.arraycopy(prefix, 0, buf, 0, prefix.length);
        writeLong(postfix, buf, prefix.length);
        return buf;
    }
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