Get transform stats API

A GetTransformStatsRequest requires a transform id or the special wildcard _all to get the statistics for all transforms.

GetTransformStatsRequest request =
        new GetTransformStatsRequest(id); 

The following arguments are optional.

request.setPageParams(new PageParams(0, 100)); 
request.setAllowNoMatch(true); 

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

GetTransformStatsResponse response =
    client.transform()
        .getTransformStats(request, RequestOptions.DEFAULT);

Synchronous calls may throw an IOException in case of either failing to parse the REST response in the high-level REST client, the request times out or similar cases where there is no response coming back from the server.

In cases where the server returns a 4xx or 5xx error code, the high-level client tries to parse the response body error details instead and then throws a generic ElasticsearchException and adds the original ResponseException as a suppressed exception to it.

Executing a GetTransformStatsRequest 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-transform-stats method:

client.transform().getTransformStatsAsync(
        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. Failure scenarios and expected exceptions are the same as in the synchronous execution case.

A typical listener for get-transform-stats looks like:

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

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

The returned GetTransformStatsResponse contains the requested transform statistics.

TransformStats stats =
    response.getTransformsStats().get(0); 
TransformStats.State state =
    stats.getState(); 
TransformIndexerStats indexerStats =
    stats.getIndexerStats(); 
TransformProgress progress =
    stats.getCheckpointingInfo()
        .getNext().getCheckpointProgress(); 
NodeAttributes node =
    stats.getNode();