How to get the result of an Activity Execution

To get the results of an asynchronously invoked Activity method, use the Promise get method to block until the Activity method result is available.

Sometimes an Activity Execution lifecycle goes beyond a synchronous method invocation. For example, a request can be put in a queue and later a reply comes and is picked up by a different Worker process. The whole request-reply interaction can be modeled as a single Activity.

To indicate that an Activity should not be completed upon its method return, call ActivityExecutionContext.doNotCompleteOnReturn() from the original Activity thread.

Then later, when replies come, complete the Activity using the ActivityCompletionClient. To correlate Activity invocation with completion use either a TaskToken or Workflow and Activity IDs.

Following is an example of using ActivityExecutionContext.doNotCompleteOnReturn():

public class FileProcessingActivitiesImpl implements FileProcessingActivities {

  public String download(String bucketName, String remoteName, String localName) {

    ActivityExecutionContext ctx = Activity.getExecutionContext();

    // Used to correlate reply
    byte[] taskToken = ctx.getInfo().getTaskToken();

    asyncDownloadFileFromS3(taskToken, bucketName, remoteName, localDirectory + localName);
    ctx.doNotCompleteOnReturn();

    // Return value is ignored when doNotCompleteOnReturn was called.
    return "ignored";
  }
  ...
}

When the download is complete, the download service potentially can complete the Activity, or fail it from a different process, for example:

  public <R> void completeActivity(byte[] taskToken, R result) {
    completionClient.complete(taskToken, result);
  }

  public void failActivity(byte[] taskToken, Exception failure) {
    completionClient.completeExceptionally(taskToken, failure);
  }