InputStream either hangs forever or SerialPortTimeputException is thrown #607

I'm using the code from this tutorial to read the answer from a COM device:

StringBuilder sb = new StringBuilder();
try {
    for(int j = 0; j < 1000; ++j) {
        char c = (char) in.read(); //InputStream in = port.getInputStream();
        System.out.print(c);
        sb.append(c);
    }
    in.close();
} catch (Exception e) {
    e.printStackTrace();
}
return sb.toString();

The print for my first command looks like this (yes, there are return characters):

OK

The problem is that the InputStream hangs/stalls after this (already tried to give it a minute), so the answer is never returned.

I've also tried a version with a ByteArrayOutputStream:
for(int length; (length = in.read(buffer)) != -1;)

Same thing here, it just stalls and never leaves the loop. The answer contains a bunch of \r or \n for some reason, so I can't just break once one of those appears (at j!=0).

I was using

port.setComPortTimeouts(SerialPort.TIMEOUT_READ_SEMI_BLOCKING, 0, 0);

and changed it to

port.setComPortTimeouts(SerialPort.TIMEOUT_READ_SEMI_BLOCKING, 5*1000, 5*1000);

Now it still prints "\nOK\n" and returns "\nOK\n" but also throws a SerialPortTimeoutException after 5 seconds.

With TIMEOUT_NONBLOCKING: Empty answer and instant exception.

What can I do here?