Код приложил. Не поленился проверить в Intellij IDEA
package com.javarush.task.task19.task1908;
import java.io.*;
import java.util.ArrayList;
/*
Выделяем числа
*/
public class Solution {
public static void main(String[] args) throws Exception{
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
FileReader file1 = new FileReader(reader.readLine());
FileWriter file2 = new FileWriter(reader.readLine());
BufferedReader fileReader = new BufferedReader(file1);
BufferedWriter fileWriter = new BufferedWriter(file2);
while(fileReader.ready()){
String[] nums = fileReader.readLine().trim().split("\\D+");
for(String s : nums){
fileWriter.write(s + " ");
}
}
reader.close();
fileReader.close();
fileWriter.close();
file2.close();
file1.close();
}
}