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Connect to MongoDB

The Java Reactive Streams driver is an implementation of the Reactive Streams API, which consists of three components:

  • Publisher

  • Subscriber

  • Subscription

A Publisher is a provider of an unbounded number of sequenced elements, published according to the demand received from its Subscriber or multiple instances of Subscriber. A Subscription represents a one-to-one lifecycle of a Subscriber subscribing to a Publisher.

Tip

To learn more about reactive streams, visit the Reactive Streams documentation.

In this tutorial, you must implement Java Reactive Streams Subscribers to query your database. This guide uses methods from the Reactor library, a library based on the Reactive Streams specification to implement Java Reactive Streams Subscribers.

To learn more about the Reactor library, see Getting Started in the Project Reactor documentation.

1

Create your Java Reactive Streams driver Application

You must use a project within an integrated development environment (IDE) to complete the following steps. In your project, create a new Java file in the Java package named QueryDatabase. Copy and paste the following code into the QueryDatabase file:

import com.mongodb.*;
import com.mongodb.reactivestreams.client.MongoCollection;
import org.bson.Document;
import reactor.core.publisher.Mono;
import com.mongodb.reactivestreams.client.MongoClient;
import com.mongodb.reactivestreams.client.MongoClients;
import com.mongodb.reactivestreams.client.MongoDatabase;
import static com.mongodb.client.model.Filters.eq;
public class QueryDatabase {
    public static void main(String[] args) {
        // Replace the placeholder with your Atlas connection string
        String uri = "<connection string>";
        // Construct a ServerApi instance using the ServerApi.builder() method
        ServerApi serverApi = ServerApi.builder()
                .version(ServerApiVersion.V1)
                .build();
        MongoClientSettings settings = MongoClientSettings.builder()
                .applyConnectionString(new ConnectionString(uri))
                .serverApi(serverApi)
                .build();
        // Create a new client and connect to the server
        try (MongoClient mongoClient = MongoClients.create(settings)) {
            MongoDatabase database = mongoClient.getDatabase("sample_mflix");
            MongoCollection<Document> movies = database.getCollection("movies");
            Mono.from(movies.find(eq("title", "Back to the Future")))                   
                    .doOnSuccess(i -> System.out.println(i))                            
                    .doOnError(err -> System.out.println("Error: " + err.getMessage())) 
                    .block();                                                           
        }
    }
}
2

Assign the Connection String

Replace the <connection string> placeholder with the connection string that you copied from the Create a Connection String step of this guide.

3

Run your Application

Run your application, either in your IDE or in your shell. The output shows that you have connected to MongoDB and queried the database.

{
   _id: ...,
   plot: 'A young man is accidentally sent 30 years into the past...',
   genres: [ 'Adventure', 'Comedy', 'Sci-Fi' ],
   ...
   title: 'Back to the Future',
   ...
 }

Tip

If you encounter an error, check whether you specified the proper connection string, and that you loaded the sample data.

After you complete these steps, you have a working application that uses the driver to connect to your MongoDB deployment, queries the database, and prints out the result.

Note

If you run into issues on this step, ask for help in the MongoDB Community Forums or submit feedback by using the Rate this page tab on the right or bottom right side of this page.

Back

Create a Connection String

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Next Steps