A GetDatafeedRequest object gets can have any number of datafeedId entries. However, they all must be non-null. An empty list is the same as requesting for all datafeeds.

GetDatafeedRequest request = new GetDatafeedRequest(datafeedId); 
request.setAllowNoDatafeeds(true); 

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

GetDatafeedResponse response = client.machineLearning().getDatafeed(request, RequestOptions.DEFAULT);

Executing a GetDatafeedRequest 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 get-datafeed method:

client.machineLearning().getDatafeedAsync(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 get-datafeed looks like:

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

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