@SpringBootApplication public class Main implements CommandLineRunner { public static void main(String[] args) { SpringApplication.run(Main.class, args); System.out.println("I am in"); } public void run(String... args) throws Exception { //Creating string reporte String reporte = ""; for (int i = 0; i < 10; i++) { reporte = reporte +"Line"+i+ "\n";// Line1\nLine2\n....... } //Creating file.txt saving the string and defining as multiline FileWriter fileWriter = new FileWriter("file.txt", true); BufferedWriter bufferedWriter = new BufferedWriter(fileWriter); bufferedWriter.write(reporte + "\n"); bufferedWriter.flush(); bufferedWriter.close(); fileWriter.close(); } }