Periodic background jobs in Ratpack

Example.java

import ratpack.exec.ExecController;
import ratpack.exec.Execution;
import ratpack.http.client.HttpClient;
import ratpack.server.RatpackServer;
import ratpack.service.Service;
import ratpack.service.StartEvent;
import ratpack.service.StopEvent;

import java.net.URI;
import java.util.Optional;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;

public class Example {

  static class ScheduledService implements Service {

    private volatile ScheduledFuture<?> nextFuture;
    private volatile boolean stopped;

    private HttpClient httpClient;
    private ScheduledExecutorService executorService;

    @Override
    public void onStart(StartEvent event) throws Exception {
      httpClient = event.getRegistry().get(HttpClient.class);
      executorService = event.getRegistry().get(ExecController.class).getExecutor();

      scheduleNext();
    }

    @Override
    public void onStop(StopEvent event) throws Exception {
      stopped = true;
      Optional.ofNullable(nextFuture).ifPresent(f -> f.cancel(true));
    }

    private void scheduleNext() {
      nextFuture = executorService.schedule(this::run, 1, TimeUnit.SECONDS);
    }

    private void run() {
      if (stopped) {
        return;
      }

      Execution.fork()
        .onComplete(e -> scheduleNext())
        .onError(Throwable::printStackTrace)
        .start(e ->
          httpClient.get(new URI("https://google.com")).then(response ->
            System.out.println("Status: " + response.getStatusCode())
          )
        );
    }
  }

  public static void main(String[] args) throws Exception {
    RatpackServer server = RatpackServer.of(s -> s
      .registryOf(r -> r.add(new ScheduledService()))
    );

    server.start();
    Thread.sleep(5000);
    server.stop();
  }
}