Accessing data from mongodb

You've to use aggregation framework. Statically import all the methods of helper classes and use the below code.

Use of BasicDBObject is deprecated in newer 3.x driver api. You should use the new class Document for similar needs.

import static com.mongodb.client.model.Accumulators.*;
import static com.mongodb.client.model.Aggregates.*;
import static java.util.Arrays.asList;
import static com.mongodb.client.model.Filters.*;
import static com.mongodb.client.model.Projections.*;
import org.bson.conversions.Bson;

MongoCollection<Document> mongoEngCollection = mongoDbReader.getCollection();

List<Bson> obj = new ArrayList<>();
//Forming query using request parameter. requestAttributes contains map of request parameters.
for(Map.Entry<PathAttribute, PathValue<?>> entry : requestAttributes.entrySet()) {
   String key = entry.getKey().getName();
   //Check if key is not date and set the start and end date
   obj.add(eq(key, entry.getValue().getRawValue()));
}

//Build aggregation stages
Bson match = match(and(obj));
Bson group = group(
              first("user", "$name"), 
              sum("total_results", 1), 
              push("results", "$$ROOT")
);
Bson projection = project(fields(excludeId()));

//Query Mongodb
List<Document> results = mongoEngCollection .aggregate(asList(match, group, projection)).into(new ArrayList<Document>());

More about aggregation here https://docs.mongodb.com/manual/reference/operator/aggregation/