byte array initialization from a int/long/short literal => byte[] array = toBytes(0x01020304);

ByteUtil.java

package com.example.util;

import java.nio.ByteBuffer;

public final class ByteUtil {

    private ByteUtil() {
    }

    /**
     * Shorthand method to init a byte array from an int.<br>
     * Usefull to get a
     * <code>new byte[] { (byte) 0x01, (byte) 0x02, (byte) 0x03, (byte) 0x04 }</code>
     * from a <code>0x01020304</code>.<br>
     * Usage: <code>byte[] array = toBytes(0x01020304);</code><br>
     * It works for 4 bytes arrays (int).<br>
     * It works for any multiple of 4 bytes arrays.<br>
     * Ex: <code>byte[] longArray = toBytes(0x01020304, 0xAABBCCDD, 0x11121314)</code>
     * 
     * @param intVal first int to convert in the resulting array (4 bytes), mandatory
     * @param intArray additional ints to add to the array (any more 4 bytes ints)
     * @return the resulting byte array
     */
    public static byte[] toBytes(final int intVal, final int... intArray) {
        if (intArray == null || (intArray.length == 0)) {
            return ByteBuffer.allocate(4).putInt(intVal).array();
        } else {
            final ByteBuffer bb = ByteBuffer.allocate(4 + (intArray.length * 4)).putInt(intVal);
            for (final int val : intArray) {
                bb.putInt(val);
            }
            return bb.array();
        }
    }

    /**
     * Shorthand method to init a byte array from a short.<br>
     * Usefull to get a
     * <code>new byte[] { (byte) 0x01, (byte) 0x02 }</code>
     * from a <code>0x0102</code>.<br>
     * Usage: <code>byte[] array = toBytes((short) 0x0102);</code><br>
     * Warning: If the literal is not cast to short, it will be treated as an int, resulting in the call to the {@link #toBytes(int, int...)} method and generating a 4 bytes buffer instead of a 2 bytes buffer.<br>
     * It works for 2 bytes arrays (short).<br>
     * It works for any multiple of 2 bytes arrays.<br>
     * Ex: <code>byte[] longArray = toBytes(0x0102, 0xAABB, 0x1112)</code>
     * 
     * @param shortVal first short to convert in the resulting array (2 bytes), mandatory
     * @param shortArray additional shorts to add to the array (any more 2 bytes shorts)
     * @return the resulting byte array
     */
    public static byte[] toBytes(final short shortVal, final short... shortArray) {
        if (shortArray == null || (shortArray.length == 0)) {
            return ByteBuffer.allocate(2).putShort(shortVal).array();
        } else {
            final ByteBuffer bb = ByteBuffer.allocate(2 + (shortArray.length * 2)).putShort(shortVal);
            for (final short val : shortArray) {
                bb.putShort(val);
            }
            return bb.array();
        }
    }

    /**
     * Shorthand method to init a byte array from a long.<br>
     * Usefull to get a
     * <code>new byte[] { (byte) 0x01, (byte) 0x02, (byte) 0x03, (byte) 0x04, (byte) 0x05, (byte) 0x06, (byte) 0x07, (byte) 0x08 }</code>
     * from a <code>0x0102030405060708L</code>.<br>
     * Usage: <code>byte[] array = toBytes(0x0102030405060708L);</code><br>
     * It works for 8 bytes arrays (long).<br>
     * It works for any multiple of 8 bytes arrays.<br>
     * Ex: <code>byte[] longArray = toBytes(0x0102030405060708L, 0xAABBCCDDEEFF0011L)</code>
     * 
     * @param intVal first long to convert in the resulting array (8 bytes), mandatory
     * @param intArray additional longs to add to the array (any more 8 bytes longs)
     * @return the resulting byte array
     */
    public static byte[] toBytes(final long longVal, final long... longArray) {
        if (longArray == null || (longArray.length == 0)) {
            return ByteBuffer.allocate(8).putLong(longVal).array();
        } else {
            final ByteBuffer bb = ByteBuffer.allocate(8 + (longArray.length * 8)).putLong(longVal);
            for (final long val : longArray) {
                bb.putLong(val);
            }
            return bb.array();
        }
    }

}