driver-legacy/src/main/com/mongodb/DBCollection.java
public Cursor aggregate(final List<? extends DBObject> pipeline, final AggregationOptions options) {
        return aggregate(pipeline, options, getReadPreference());
    }
public Cursor aggregate(final List<? extends DBObject> pipeline, final AggregationOptions options) {
        return aggregate(pipeline, options, getReadPreference());
    }
Method implements aggregation framework.

@param pipeline operations to be performed in the aggregation pipeline
@param options  options to apply to the aggregation
@return the aggregation operation's result set
@mongodb.driver.manual core/aggregation-pipeline/ Aggregation
@mongodb.server.release 2.2