public static String readTask(String collectionName)
{
    MongoClient mongoClient = new MongoClient();
    MongoDatabase database = mongoClient.getDatabase("exampleDatabase");

    Bson lookup = new Document("$lookup",
            new Document("from", "Project")
                    .append("localField", "project._id")
                    .append("foreignField", "_id")
                    .append("as", "something"));

    List<Bson> filters = new ArrayList<>();
    filters.add(lookup);

    AggregateIterable<Document> it = database.getCollection(collectionName).aggregate(filters);
    System.out.println("First Document: " + it.first().toString());

    return it.toString();
}

{
    _id = 599a62cac29d9a2684c64012,
    constructionRoomNumber = 1,
    type = 2,
    summary = 3,
    description = 4,
    status = Open,
    project = {
        "$ref": "Project",
        "$id": "5996582a0983347784fb2ff4"
    },
    something = []
}

_id: ObjectId('5996582a0983347784fb2ff4')
projectCode: "V1000"
projectName: "Example Project"
projectLocation: "1 Somewhere Street, Some City"
clientName: "Whatever Client"
isActive: true

_id: ObjectId('599a62cac29d9a2684c64012')
constructionRoomNumber: "15"
type: "Example"
summary: "Summary Text"
description: "Description Text"
status: "Open"
project: DBRef(Project, 5996582a0983347784fb2ff4, undefined)

_id: ObjectId('599a62cac29d9a2684c64012')
constructionRoomNumber: "15"
type: "Example"
summary: "Summary Text"
description: "Description Text"
status: "Open"
project: {
    _id: ObjectId('5996582a0983347784fb2ff4')
    projectCode: "V1000"
    projectName: "Example Project"
    projectLocation: "1 Somewhere Street, Some City"
    clientName: "Whatever Client"
    isActive: true
}