// 1. The database for reactive, real-time applications
MongoClient mongoClient;

// Create a new MongoClient with a MongoDB URI string.
if (args.length == 0) {
// Defaults to a localhost replicaset on ports: 27017, 27018, 27019
  mongoClient = new MongoClient(new
  MongoClientURI("mongodb://localhost:27017,localhost:27018,localhost:27019"));
} else {
  mongoClient = new MongoClient(new MongoClientURI(args[0]));
}

// Select the MongoDB database.
MongoDatabase database = mongoClient.getDatabase("testChangeStreams");

// Select the collection to query.
MongoCollection<Document> collection = database.getCollection("documents");

// Create the change stream cursor.
MongoCursor<Document> cursor = collection.watch().iterator();

// 2. Tunable consistency controls
String connectionString = "mongodb://localhost/?readPreference=secondaryPreferred";
 
MongoClient client = new MongoClient(new MongoClientURI(connectionString);
 
MongoDatabase database = client.getDatabase("myDatabase");
MongoCollection<Document> collection = database.getCollection("myCollection");
 
// Start client session, which is causally consistent by default
try (ClientSession session = client.startSession(ClientSessionOptions.builder().build())) {
  //Run causally related operations within the session
  collection.insertOne(session, ...);
  collection.updateOne(session, ...);
 
  try (MongoCursor<Document> cursor = collection.find(session).filter(...).iterator()) {
    while (cursor.hasNext()) {
      Document cur = cursor.next();
    }
  }
}

// 3. Exploiting the power of arrays
MongoCollection<Document> collection = client
  .getDatabase("test")
  .getCollection("arrayUpdatesTest");

collection.updateOne(
  Filters.eq("_id", 1),
  Updates.set("a.$[i].b", 2),

new UpdateOptions()
  .arrayFilters(
    Collections.singletonList(
      Filters.eq("i.b", 0))));