ByteBuffer buffer = ByteBuffer.allocate(1024);
buffer.put("aabcde".getBytes());
byte[] bytes = new byte[buffer.remaining()];
buffer.get(bytes);
String s = new String(bytes);

위가 아니라 아래처럼 해야 됩니다. ^^;;

ByteBuffer buffer = ByteBuffer.allocate(1024);
buffer.put("aabcde".getBytes());
byte[] bytes = new byte[buffer.position()];
buffer.flip();       
buffer.get(bytes);
String s = new String(bytes);
System.out.println(s);

public int byteArrayToInt(byte [] b) {
return (b[0] << 24) + ((b[1] & 0xFF) << 16) + ((b[2] & 0xFF) << 8) + (b[3] & 0xFF);
}

public byte[] intToByteArray(int value) {
  return new byte[] {(byte)(value >>> 24), (byte)(value >>> 16), (byte)(value >>> 8), (byte)value};
}