title: How can I wait until an S3 file is updated?
body: <p>So I have a JVM web service, and I want to know when an S3 bucket is updated. I know s3 has event notifications, but from what I've read those are more like hooks that you can configure to send a message to a lambda function, for example.</p>
  <p>Is there a way to do this from within an app? Something like <code>MyBucket.WaitUpdate().Then(...do something...)</code>. The alternative is to just poll periodically, but I'd rather be more responsive to changes.</p>