Convert long to byte array and add it to another array

There are multiple ways to do it:

• Use a ByteBuffer (best option - concise and easy to read):

  byte[] bytes = ByteBuffer.allocate(Long.SIZE / Byte.SIZE).putLong(someLong).array();

• You can also use DataOutputStream (more verbose):

  ByteArrayOutputStream baos = new ByteArrayOutputStream();DataOutputStream dos = new DataOutputStream(baos);dos.writeLong(someLong);dos.close();byte[] longBytes = baos.toByteArray();

• Finally, you can do this manually (taken from the LongSerializer in Hector's code) (harder to read):

  byte[] b = new byte[8];for (int i = 0; i < size; ++i) {  b[i] = (byte) (l >> (size - i - 1 << 3));}

Then you can append these bytes to your existing array by a simple loop:

// change this, if you want your long to start from // a different position in the arrayint start = 0; for (int i = 0; i < longBytes.length; i ++) {   bytes[start + i] = longBytes[i];}

If you want to really get under the hood...

public byte[] longToByteArray(long value) {    return new byte[] {        (byte) (value >> 56),        (byte) (value >> 48),        (byte) (value >> 40),        (byte) (value >> 32),        (byte) (value >> 24),        (byte) (value >> 16),        (byte) (value >> 8),        (byte) value    };}

For me ByteBuffer and other utils are expensive from time perspective. Here are 2 methods that you can use:

// first method (that is using the second method), it return the array allocated and fulfilled

public byte[] longToByteArray(long value) {        byte[] array = new byte[8];        longToByteArray(value,array,0);        return array;}

// this method is useful if you have already allocated the buffer and you want to write the long a specific location in the array.

public void longToByteArray(long value, byte[] array, int startFrom) {    for (int i=7; i>=0; i--)    {        array[startFrom+7-i] = (byte) (value >> i*8);    }}