> I suppose it would be much harder to do it without the transferTo function,

No, it would not:

    public class Test {
        public static void main(String[] args) throws Exception {
            byte[] buf = new byte[4096];
            int read;
            while ((read = System.in.read(buf)) > 0) {
                System.out.write(buf, 0, read);
            }
        }
    }

I imagine it will look pretty much the same in the majority of languages which have similar I/O abstractions.