Some useful methods for handling byte arrays.

ByteUtils.java

package de.struckmeierfliesen.nxt.linefollower;

import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.List;

public class ByteUtils {
	private ByteUtils() {}
	private static final byte MAX_BYTE = (byte) 0xff;
	private static final byte NULL = 0x00 & MAX_BYTE;
	private static final byte START_OF_HEADER = 0x01 & MAX_BYTE;
	private static final byte START_OF_CONTENT = 0x02 & MAX_BYTE;
	private static final byte END_OF_MESSAGE = 0x03 & MAX_BYTE;
	private static final int SIZEOF_LONG = Long.SIZE / Byte.SIZE;
	
	
	public static byte[] listToArray(List<Byte> list) {
		byte[] bytes = new byte[list.size()];
		for (int i = 0; i < list.size(); i++) {
			bytes[i] = list.get(i);
		}
		return bytes;
	}
	
	public static String arrayToString(byte[] bytes) {
		return new String(bytes, "UTF-8");
	}
	
	public static String listToString(List<Byte> list) {
		return arrayToString(listToArray(list));
	}

	public static byte[] packMessage(byte[] header, byte[] content) {
		int length = header.length + content.length + 3;
		List<Byte> bytes = new ArrayList<>(length);
		bytes.add(START_OF_HEADER);
		for (byte b : header) bytes.add(b);
		bytes.add(START_OF_CONTENT);
		for (byte b : content) bytes.add(b);
		bytes.add(END_OF_MESSAGE);
		
		return listToArray(bytes);
	}

	public static byte[][] unpackMessage(byte[] bytes) {
		List<Byte> header = new ArrayList<>();
		List<Byte> content = new ArrayList<>();

		byte lastDescriptor = NULL;
		loop: for (byte b : bytes) {
			switch (lastDescriptor) {
				case NULL:
					if (b == START_OF_HEADER) {
						lastDescriptor = b;
					}
					break;
				case START_OF_HEADER:
					if (b == START_OF_CONTENT) {
						lastDescriptor = b;
					} else {
						header.add(b);
					}
					break;
				case START_OF_CONTENT:
					if (b == END_OF_MESSAGE) {
						lastDescriptor = b;
					}else {
						content.add(b);
					}
					break;
				case END_OF_MESSAGE:
					break loop;
			}
		}
		return new byte[][] {listToArray(header), listToArray(content)};
	}

	public static byte[] longToBytes(long val) { // taken from org.apache.hadoop.hbase.util.Bytes
		byte [] b = new byte[8];
		for (int i = 7; i > 0; i--) {
			b[i] = (byte) val;
			val >>>= 8;
		}
		b[0] = (byte) val;
		return b;
	}
	
	public static long bytesToLong(byte[] bytes) { // taken from org.apache.hadoop.hbase.util.Bytes
		long l = 0;
		for(int i = 0; i < SIZEOF_LONG; i++) {
			l <<= 8;
			l ^= bytes[i] & 0xFF;
		}
		return l;
	}
}