At work, we have 5 RFID readers attached to a PC running Linux. The readers are all recognized as keyboards and send their input (what they read form the Chip) as an key-input-event sequence. To be able to tell which reader send what sequence, I'm doing a raw-read over /dev/input/XX and get their input this way.
The problem with this is, that the send keyboard-events generated by the RFID readers are still "in" stdin and when I try to read from System.in via Scanner (input should be generated by a normal keyboard this time), I first get the "pending" input from the readers (which consists of 10 Hex-decimal digits and a newline (\n)).
Now, the question is: How can I flush all these "pending" input's from stdin and then read what I really want from the keyboard?
I tried:
System.in.skip(System.in.available());
But seek is not allowed on stdin (skip throws an IOException).
for (int i = 0; i < System.in.available(); i++){
System.in.read();
}
But available() doesn't estimate enough (still stuff in stdin afterwards).
Scanner scanner = new Scanner(System.in);
while (scanner.hasNextLine()){
scanner.nextLine();
}
System.out.println("Clean!");
But hasNextLine() never becomes false (the print never executes).
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
String line;
while ((line = in.readLine()) != null);
System.out.println("Clean!");
Same as above.
Anyone with any more ideas?
Based on @Joni's advice, i put this together:
Scanner scanner = new Scanner(System.in);
int choice = 0;
while (scanner.hasNext()){
if (scanner.hasNextInt()){
choice = scanner.nextInt();
break;
} else {
scanner.next(); // Just discard this, not interested...
}
}
This discards the data that is already "pending" in stdin and waits until valid data is entered. Valid, in this context, meaning a decimal integer.