A PreviewDatafeedRequest object is created referencing a non-null datafeedId.

PreviewDatafeedRequest request = new PreviewDatafeedRequest(datafeedId); 

When executing a PreviewDatafeedRequest in the following manner, the client waits for the PreviewDatafeedResponse to be returned before continuing with code execution:

PreviewDatafeedResponse response = client.machineLearning().previewDatafeed(request, RequestOptions.DEFAULT);

Executing a PreviewDatafeedRequest can also be done in an asynchronous fashion so that the client can return directly. Users need to specify how the response or potential failures will be handled by passing the request and a listener to the asynchronous preview-datafeed method:

client.machineLearning().previewDatafeedAsync(request, RequestOptions.DEFAULT, listener); 

The asynchronous method does not block and returns immediately. Once it is completed the ActionListener is called back using the onResponse method if the execution successfully completed or using the onFailure method if it failed.

A typical listener for preview-datafeed looks like:

ActionListener<PreviewDatafeedResponse> listener = new ActionListener<PreviewDatafeedResponse>() {
    @Override
    public void onResponse(PreviewDatafeedResponse response) {
        
    }

    @Override
    public void onFailure(Exception e) {
        
    }
};