How to get the max timestamp of the current slidin

问题:

I'm using a sliding time window of X size and Y period. In order to mark the output of each window, I'd like to get the timestamp of the current window of PCollection.

    PCollection<T> windowedInput = input
      .apply(Window<T>into(
          SlidingWindows.of(Duration.standardMinutes(10))
                        .every(Duration.standardMinutes(1))));

   // Extract key from each input and run a function per group.
   //
   // Q: ExtractKey() depends on the window triggered time.
   //    How can I pass the timestamp of windowedInputs to ExtractKey()?
   PCollection<KV<K, Iterable<T>>> groupedInputs = windowedInputs
     .apply(ParDo.of(new ExtractKey()))
     .apply(GroupByKey.<K, Ts>create());

   // Run Story clustering and write outputs.
   //
   // Q: Also I'd like to add a window timestamp suffix to the output.
   //    How can I pass (or get) the timestamp to SomeDoFn()?
   PCollection<String> results = groupedInputs.apply(ParDo.of(new SomeDoFn()));

回答1:

A DoFn is allowed to access the window of the current element via an optional BoundedWindow parameter on the @ProcessElement method:

class SomeDoFn extends DoFn<KV<K, Iterable<T>>, String> {
  @ProcessElement
  public void process(ProcessContext c, BoundedWindow window) {
    ...
  }
}