InputStream either hangs forever or SerialPortTimeputException is thrown

[Nathipha]

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?

[Nathipha]

Haven't managed to get it to run yet but at least the version here is working, so that's what I'm using now:

while (port.bytesAvailable() == 0) {
    Thread.sleep(20);
}

byte[] readBuffer = new byte[port.bytesAvailable()];
int numRead = port.readBytes(readBuffer, readBuffer.length);
System.out.println("Read " + numRead + " bytes.");
String bytes = new String(readBuffer, StandardCharsets.UTF_8);

Careful:

1. You have to close the port with port.closePort() before you try to get it with SerialPort.getCommPorts() again! The docs say that calling openPort on a port that is already open "will simply reconfigure the port parameters" but for me isOpen() always returns false at that point (even though it should still be open) but it also fails to open it again (I'm always trying twice)!
2. When you're sending a text message, there is going to be a delay between sending the "AT+CMGS" command and receiving a "good" reply! At first it always replies with a \n for some reason, which triggers the while to stop. The actual reply (+CMGS: 12\nOK, 12=message ID) doesn't come along until 1-3 seconds later, when you're probably already trying to send the next message. That's why: Use while (port.bytesAvailable()==0 || port.bytesAvailable()==2). The shortest, valid reply in my app is "OK" (including a bunch of extra \r), so for me it shouldn't cause a problem. I also set the sleep timer to 50 and it's still fast enough.
3. Do NOT use multiple threads to send multiple messages at the same time, it's going to mix up the commands and nothing is going to work in the end! Using a single thread with a loop seems to be fine.