Connect to MongoDB

Use MongoClients.create() to make a connection to a running MongoDB instance.


The following examples are not meant to provide an exhaustive list of ways to instantiate MongoClient. For a complete list of MongoClients factory methods, see the MongoClients API documentation.


It is strongly recommended that system keep-alive settings should be configured with shorter timeouts.

See the ‘does TCP keep-alive time affect MongoDB deployments?’ documentation for more information.


  • Running MongoDB deployments to which to connect. For example, to connect to a standalone, you must have a running standalone.

  • The MongoDB Driver. See Installation for instructions on how to install the MongoDB driver.

  • The following import statements:

import com.mongodb.reactivestreams.client.MongoClients;
import com.mongodb.reactivestreams.client.MongoClient;
import com.mongodb.MongoClientSettings;
import com.mongodb.ConnectionString;
import com.mongodb.ServerAddress;
import com.mongodb.MongoCredential;

import java.util.Arrays;


A MongoClient instance represents a pool of connections to the database; you will only need one instance of class MongoClient even with multiple concurrent operations.


Typically you only create one MongoClient instance for a given MongoDB deployment (e.g. standalone, replica set, or a sharded cluster) and use it across your application. However, if you do create multiple instances:

  • All resource usage limits (e.g. max connections, etc.) apply per MongoClient instance.

  • To dispose of an instance, call MongoClient.close() to clean up resources.

Connect to a Standalone MongoDB Instance

To connect to a standalone MongoDB instance:

  • You can create a MongoClient object without any parameters to connect to a MongoDB instance running on localhost on port 27017:
    MongoClient mongoClient = MongoClients.create()
  • You can explicitly specify the hostname to connect to a MongoDB instance running on the specified host on port 27017:
    MongoClient mongoClient = MongoClients.create("mongodb://host1");
  • You can explicitly specify the hostname and the port:

    MongoClient mongoClient = MongoClients.create("mongodb://host1:27017");

Connect to a Replica Set

To connect to a replica set, you must specify one or more members to the MongoClients create method.


MongoDB will auto-discover the primary and the secondaries.

  • You can specify the members using a ConnectionString:

    • To specify at least two members of the replica set:
    MongoClient mongoClient = MongoClients.create("mongodb://host1:27017,host2:27017,host3:27017");
  • With at least one member of the replica set and the replicaSet option specifying the replica set name:
    MongoClient mongoClient = MongoClients.create("mongodb://host1:27017,host2:27017,host3:27017/?replicaSet=myReplicaSet");
  • You can specify a list of the all the replica set members’ ServerAddress:
    MongoClient mongoClient = MongoClients.create(
                    .applyToClusterSettings(builder ->
                                    new ServerAddress("host1", 27017),
                                    new ServerAddress("host2", 27017),
                                    new ServerAddress("host3", 27017))))

Connect to a Sharded Cluster

To connect to a sharded cluster, specify the mongos instance or instances to a MongoClients create method.

To connect to a single mongos instance:

    MongoClient mongoClient = MongoClients.create( "mongodb://localhost:27017" );

or leave the connection string out if the mongos is running on localhost:27017:

    MongoClient mongoClient = MongoClients.create();

To connect to multiple mongos instances:

  • You can specify the ConnectionString with their hostnames and ports:

    MongoClient mongoClient = MongoClients.create("mongodb://host1:27017,host2:27017");
  • You can specify a list of the mongos instances’ ServerAddress:

    MongoClient mongoClient = MongoClients.create(
                    .applyToClusterSettings(builder ->
                                    new ServerAddress("host1", 27017),
                                    new ServerAddress("host2", 27017))))

Connection Options

You can specify the connection settings using either the ConnectionString or MongoClientSettings or both.

For example, you can specify TLS/SSL and authentication setting in the connection string:

    MongoClient mongoClient = MongoClients.create("mongodb://user1:pwd1@host1/?authSource=db1&ssl=true");

You can also use MongoClientSettings to specify TLS/SSL and the MongoCredential for the authentication information:

    String user; // the user name
    String database; // the name of the database in which the user is defined
    char[] password; // the password as a character array
    // ...

    MongoCredential credential = MongoCredential.createCredential(user, database, password);

    MongoClientSettings settings = MongoClientSettings.builder()
            .applyToSslSettings(builder -> builder.enabled(true))
            .applyToClusterSettings(builder -> 
                builder.hosts(Arrays.asList(new ServerAddress("host1", 27017))))

    MongoClient mongoClient = MongoClients.create(settings);

Finally, in some cases you may need to combine a connection string with programmatic configuration:

    ConnectionString connectionString = new ConnectionString("mongodb://host1:27107,host2:27017/?ssl=true");
    CommandListener myCommandListener = ...;
    MongoClientSettings settings = MongoClientSettings.builder()

    MongoClient mongoClient = MongoClients.create(settings);