Easy way to concatenate two byte arrays

Question

What is the easy way to concatenate two byte arrays?

Say,

byte a[];
byte b[];

How do I concatenate two byte

Answer 1

You can use third party libraries for Clean Code like Apache Commons Lang and use it like:

byte[] bytes = ArrayUtils.addAll(a, b);

Answer 2

Here's a nice solution using Guava's com.google.common.primitives.Bytes:

byte[] c = Bytes.concat(a, b);

The great thing about this method is that it has a varargs signature:

public static byte[] concat(byte[]... arrays)

which means that you can concatenate an arbitrary number of arrays in a single method call.

Answer 3

byte[] result = new byte[a.length + b.length];
// copy a to result
System.arraycopy(a, 0, result, 0, a.length);
// copy b to result
System.arraycopy(b, 0, result, a.length, b.length);

Answer 4

Most straightforward:

byte[] c = new byte[a.length + b.length];
System.arraycopy(a, 0, c, 0, a.length);
System.arraycopy(b, 0, c, a.length, b.length);

Answer 5

The most elegant way to do this is with a ByteArrayOutputStream.

byte a[];
byte b[];

ByteArrayOutputStream outputStream = new ByteArrayOutputStream( );
outputStream.write( a );
outputStream.write( b );

byte c[] = outputStream.toByteArray( );

Answer 6

If you prefer ByteBuffer like @kalefranz, there is always the posibility to concatenate two byte[] (or even more) in one line, like this:

byte[] c = ByteBuffer.allocate(a.length+b.length).put(a).put(b).array();