How to pass custom MyPipelineOptions to Google Dataflow DoFN? - google-cloud-dataflow

Question

when I try to add MyPipelineOptions parameter to my Google Dataflow DoFN as documented, I get a compiler error:
java.lang.IllegalArgumentException:
com.xxx.MyProcessor,
#ProcessElement parseItem(PubsubMessage, MyPipelineOptions, OutputReceiver),
#ProcessElement parseItem(PubsubMessage, MyPipelineOptions, OutputReceiver),
parameter of type MyPipelineOptions at index 1:
MyPipelineOptions is not a valid context parameter.
Should be one of [BoundedWindow, RestrictionTracker<?, ?>]
If I change MyPipelineOptions to PipelineOptions, the error is gone, but if I try to cast back to MyPipelineOptions inside my function, I get a ClassCastException so I'm guessing it's not the right way... Any idea how I pass my custom options class to the element processors?
Here's the code structure:
import org.apache.beam.runners.dataflow.options.DataflowPipelineOptions;
public interface MyPipelineOptions extends DataflowPipelineOptions {
...
}
public class MyProcessor extends DoFn<PubsubMessage, String> {
#ProcessElement
public void parseItem(#Element PubsubMessage message, MyPipelineOptions po, OutputReceiver<String> out) throws Exception {
...
}
}
Note the docs only show an example of non-custom PipelineOptions:
PipelineOptions: The PipelineOptions for the current pipeline can always be accessed in a process method by adding it as a parameter:
.of(new DoFn<String, String>() {
public void processElement(
#Element String word, PipelineOptions options) {
}
})

Answer 1

Ok found the problem. The argument PipelineOptions is a proxy. In order to get it correctly I need to do this:
public class MyProcessor extends DoFn<PubsubMessage, String> {
#ProcessElement
public void parseItem(
#Element PubsubMessage message,
PipelineOptions po,
OutputReceiver<String> out) throws Exception {
MyPipelineOptions opts = po.as(MyPipelineOptions.class);
...
}
}
}