Appending a byte[] to the end of another byte[] [duplicate]

Question

I have two byte[] arrays which are of unknown length and I simply want to append one to the end of the other, i.e.:

byte[] ciphertext = blah; byte[] mac = blah; byte[] out = ciphertext + mac; 

I have tried using arraycopy() but can't seem to get it to work.

Answer 1

Using System.arraycopy(), something like the following should work:

// create a destination array that is the size of the two arrays byte[] destination = new byte[ciphertext.length + mac.length];  // copy ciphertext into start of destination (from pos 0, copy ciphertext.length bytes) System.arraycopy(ciphertext, 0, destination, 0, ciphertext.length);  // copy mac into end of destination (from pos ciphertext.length, copy mac.length bytes) System.arraycopy(mac, 0, destination, ciphertext.length, mac.length); 

Answer 2

Perhaps the easiest way:

ByteArrayOutputStream output = new ByteArrayOutputStream();  output.write(ciphertext); output.write(mac);  byte[] out = output.toByteArray();