[java] Gets byte array from a ByteBuffer in java

Is this the recommended way to get the bytes from the ByteBuffer

ByteBuffer bb =..

byte[] b = new byte[bb.remaining()]
bb.get(b, 0, b.length);

Depends what you want to do.

If what you want is to retrieve the bytes that are remaining (between position and limit), then what you have will work. You could also just do:

ByteBuffer bb =..

byte[] b = new byte[bb.remaining()];
bb.get(b);

which is equivalent as per the ByteBuffer javadocs.

If one does not know anything about the internal state of the given (Direct)ByteBuffer and wants to retrieve the whole content of the buffer, this can be used:

ByteBuffer byteBuffer = ...;
byte[] data = new byte[byteBuffer.capacity()];
((ByteBuffer) byteBuffer.duplicate().clear()).get(data);

Note that the bb.array() doesn't honor the byte-buffers position, and might be even worse if the bytebuffer you are working on is a slice of some other buffer.

I.e.

byte[] test = "Hello World".getBytes("Latin1");
ByteBuffer b1 = ByteBuffer.wrap(test);
byte[] hello = new byte[6];
b1.get(hello); // "Hello "
ByteBuffer b2 = b1.slice(); // position = 0, string = "World"
byte[] tooLong = b2.array(); // Will NOT be "World", but will be "Hello World".
byte[] world = new byte[5];
b2.get(world); // world = "World"

Which might not be what you intend to do.

If you really do not want to copy the byte-array, a work-around could be to use the byte-buffer's arrayOffset() + remaining(), but this only works if the application supports index+length of the byte-buffers it needs.

As simple as that

  private static byte[] getByteArrayFromByteBuffer(ByteBuffer byteBuffer) {
    byte[] bytesArray = new byte[byteBuffer.remaining()];
    byteBuffer.get(bytesArray, 0, bytesArray.length);
    return bytesArray;
}

final ByteBuffer buffer;
if (buffer.hasArray()) {
    final byte[] array = buffer.array();
    final int arrayOffset = buffer.arrayOffset();
    return Arrays.copyOfRange(array, arrayOffset + buffer.position(),
                              arrayOffset + buffer.limit());
}
// do something else

This is a simple way to get a byte[], but part of the point of using a ByteBuffer is avoiding having to create a byte[]. Perhaps you can get whatever you wanted to get from the byte[] directly from the ByteBuffer.