code: public static ByteBuffer copy(ByteBuffer src, ByteBuffer dest, int length) {
  		return copy(src, src.position(), dest, dest.position(), length);
  	}
docs: 拷贝ByteBuffer
  
  @param src 源ByteBuffer
  @param dest 目标ByteBuffer
  @param length 长度
  @return 目标ByteBuffer