non-blocking IO

public List<String> readFile(String file){
 try {
  Path path = Paths.get(file);
  return Files.readAllLines(path,
           StandardCharsets.UTF_8);
 } catch (IOException e) {
 // io exception reading from file...
 }
  return null;
}

public void writeToFile(String file, List<String> lines){
 try {
  Path path = Paths.get(file);
  Files.write(path, lines);
 } catch (IOException e) {
 // io exception writing to file...
 }
}