Monitoring Spring @Scheduled tasks

Spring's @Scheduled is convenient and silent. The default scheduler has a single thread, so one stuck task blocks every other scheduled task in the app, and nothing reports it.

Ping when the task finishes

@Scheduled(cron = "0 0 3 * * *", zone = "UTC")
public void nightlyExport() {
    try {
        exportService.run();
        heartbeat("");
    } catch (Exception e) {
        heartbeat("/fail");
        throw e;
    }
}

private void heartbeat(String suffix) {
    try {
        HttpClient.newHttpClient().send(
            HttpRequest.newBuilder(URI.create("https://cronpup.com/p/YOUR-UUID" + suffix))
                .timeout(Duration.ofSeconds(10)).build(),
            HttpResponse.BodyHandlers.discarding());
    } catch (Exception ignored) { /* never fail the job because the ping failed */ }
}

Note that Spring cron expressions have six fields (seconds first). The monitor uses the usual five: 0 3 * * * in UTC.

Catch hung tasks

Send /start when the task begins. If the finish ping doesn't follow within the grace period, you get a "started but didn't finish" alert, which is the stuck-thread-pool case. Try it free.