How not to read ints from file

import java.io.File;
import java.io.PrintWriter;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.Arrays;
import java.util.stream.IntStream;

public class Main {

    public static void main(String[] args) throws Exception {
        PrintWriter a;
        (a = new PrintWriter(new File("a.out"))).println(Arrays.stream(
                new String(Files.readAllBytes(Paths.get("a.in"))).split("[\\D]+")).flatMapToInt(n -> IntStream.of(Integer.parseInt(n))).sum());
        a.close();
    }
}