How to connect to MongoDB 3.2 in Java with username and password?

I'm using MongoDB 3.2 in my application. The code below demonstrates database initialization logic:

private void dbInit(String dbName) {

    String mongoClientURI = "mongodb://" + DB_URL + ":" + DB_PORT;
    MongoClientURI connectionString = new MongoClientURI(mongoClientURI);

    // enable SSL connection
    MongoClientOptions.builder().sslEnabled(true).build();

    if (this.mongoClient == null) {
        this.mongoClient = new MongoClient(connectionString);
    }

    // create database if doesn't exist
    this.mongoClient.getDatabase(dbName);
}

This code works fine, now I want to introduce access level separation to database.

The steps to do that:

1. Define users:

use myAppDB
db.createUser(
   {
      "user": "myAdmin",
      "pwd": "123090d1487dd4ab7",
      roles: [ "readWrite", "dbAdmin" ]
   }
)

use myAppDB
db.createUser(
   {
      "user": "guest",
      "pwd": "guest",
      roles: [ "read" ]
   }
)

2. Re-create the MongoDB 3.2 service in authentication mode: "C:\Program Files\MongoDB\Server\3.2\bin\mongod.exe" --install --dbpath=C:\data\db --logpath=C:\data\log\log.txt --auth --service. And run it.

3. Change the mongoClientURI connection string to

String mongoClientURI = "mongodb://" + DB_SRV_USR + ":" + DB_SRV_PWD + "@" + DB_URL + ":" + DB_PORT;

where DB_SRV_USR = myAdmin and DB_SRV_PWD = 123090d1487dd4ab7.

4. Check the authenticated connection in IDEA's Mongo Explorer with the same credentials, everything is OK.

5. Execute my application and get exception Authentication failed.

My questions:

1. How to connect to MongoDB 3.2 in Java with username and password? I saw a couple of examples but they are using deprecated methods.

2. Should I add my users to myAppDB or to admin table? In some tutorials I saw that users are created in admin table is it a good idea or it worth to create users only in a database they are going to work with?

As MarkusWMahlberg correctly noted, it is necessary to note the database name in the connection string.

For instance:

String mongoClientURI = "mongodb://" + DB_SRV_USR + ":" + DB_SRV_PWD + "@" + DB_URL + ":" + DB_PORT + "/" + dbName;