MongoDB Java

last modified January 27, 2024

In this article we show how to work with MongoDB in Java. There is a concise Java tutorial on ZetCode.

MongoDB is a NoSQL cross-platform document-oriented database. It is one of the most popular databases available. MongoDB is developed by MongoDB Inc. and is published as free and open-source software.

A record in MongoDB is a document, which is a data structure composed of field and value pairs. MongoDB documents are similar to JSON objects. The values of fields may include other documents, arrays, and arrays of documents. MongoDB stores documents in collections. Collections are analogous to tables in relational databases and documents to rows.

MongoDB represents JSON documents in binary-encoded format called BSON behind the scenes. BSON extends the JSON model to provide additional data types, ordered fields, and to be efficient for encoding and decoding within different languages. The .NET driver uses BsonDocument to represent BSON.

Installing MongoDB

The following command can be used to install MongoDB on a Debian-based Linux.

$ sudo apt-get install mongodb

The command installs the necessary packages that come with MongoDB.

$ sudo service mongodb status
mongodb start/running, process 975

With the sudo service mongodb status command we check the status of the mongodb server.

$ sudo service mongodb start
mongodb start/running, process 6448

The mongodb server is started with the sudo service mongodb start command.

Creating a database

The mongo tool is an interactive JavaScript shell interface to MongoDB, which provides an interface for systems administrators as well as a way for developers to test queries and operations directly with the database.

$ mongo testdb
MongoDB shell version v4.0.7
connecting to: mongodb://127.0.0.1:27017/testdb?gssapiServiceName=mongodb
...
> db
testdb
> db.cars.insert({name: "Audi", price: 52642})
> db.cars.insert({name: "Mercedes", price: 57127})
> db.cars.insert({name: "Skoda", price: 9000})
> db.cars.insert({name: "Volvo", price: 29000})
> db.cars.insert({name: "Bentley", price: 350000})
> db.cars.insert({name: "Citroen", price: 21000})
> db.cars.insert({name: "Hummer", price: 41400})
> db.cars.insert({name: "Volkswagen", price: 21600})

We create a testdb database and insert eight documents in the cars collection.

Java MongoDB driver

We use the following Maven declaration to include the MongoDB Java driver in our project.

<dependency>
    <groupId>org.mongodb</groupId>
    <artifactId>mongo-java-driver</artifactId>
    <version>x.y.z</version>
</dependency>

It is an all-in-one JAR, which embeds the core driver and BSON. BSON, short for Bin­ary JSON, is a bin­ary-en­coded seri­al­iz­a­tion of JSON-like doc­u­ments.

Java MongoDB list database collections

The first example connects to the testdb database and retrieves its collections.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
         http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.zetcode</groupId>
    <artifactId>mongocommand</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>11</maven.compiler.source>
        <maven.compiler.target>11</maven.compiler.target>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.mongodb</groupId>
            <artifactId>mongo-java-driver</artifactId>
            <version>3.10.2</version>
        </dependency>
    </dependencies>

</project>

This is our pom.xml file.

package com.zetcode;

import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoDatabase;

import java.util.logging.Level;
import java.util.logging.Logger;

public class MongoListCollections {

    public static void main(String[] args) {

        Logger mongoLogger = Logger.getLogger("org.mongodb.driver");
        mongoLogger.setLevel(Level.SEVERE);

        try (var mongoClient = MongoClients.create("mongodb://localhost:27017")) {

            MongoDatabase database = mongoClient.getDatabase("testdb");

            for (String name : database.listCollectionNames()) {

                System.out.println(name);
            }
        }
    }
}

The example connects to the testdb database and retrieves all its collections.

Logger mongoLogger = Logger.getLogger("org.mongodb.driver");
mongoLogger.setLevel(Level.SEVERE);

We set the logging level for MongoDB. We only show SEVERE error messages.

try (var mongoClient = MongoClients.create("mongodb://localhost:27017")) {

A MongoClient class is used to connect to the MongoDB server. It is created with the MongoClients.create method call. The 27017 is the default port on which the MongoDB server listens.

MongoDatabase database = mongoClient.getDatabase("testdb");

With the getDatabase method, we retrieve the testdb database.

for (String name : database.listCollectionNames()) {

    System.out.println(name);
}

The listCollectionNames method finds all the collections in the testdb database.

cars
cities

In our database, we have these two collections.

Java MongoDB database statistics

The next example connects to the testdb database and gets its statistics.

package com.zetcode;

import com.mongodb.client.MongoClients;
import org.bson.Document;

import java.util.Map;

public class MongoCommand {

    public static void main(String[] args) {

        try (var mongoClient = MongoClients.create("mongodb://localhost:27017")) {

            var database = mongoClient.getDatabase("testdb");

            var stats = database.runCommand(new Document("dbstats", 1));

            for (Map.Entry<String, Object> set : stats.entrySet()) {

                System.out.format("%s: %s%n", set.getKey(), set.getValue());
            }
        }
    }
}

The example connects to the testdb database and executes the dbstats command. It shows some database statistics.

var stats = database.runCommand(new Document("dbstats", 1));

With the runCommand method, we execute the dbstats command. The command returns a Document, which is a representation of a MongoDB document as a map.

for (Map.Entry<String, Object> set : stats.entrySet()) {

    System.out.format("%s: %s%n", set.getKey(), set.getValue());
}

We iterate through the entries of the document.

db: testdb
collections: 2
views: 0
objects: 9
avgObjSize: 48.111111111111114
dataSize: 433.0
storageSize: 57344.0
numExtents: 0
indexes: 2
indexSize: 57344.0
fsUsedSize: 1.4818904064E11
fsTotalSize: 2.547211264E11
ok: 1.0

Java MongoDB read data

MongoCollection is used to store mongo documents returned from a collection. MongoCursor is a cursor to iterate through the results of a database query. It makes sure that it is closed in case of an exception.

package com.zetcode;

import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoCursor;
import org.bson.Document;

import java.util.ArrayList;

public class MongoReadAll {

    public static void main(String[] args) {

        try (var mongoClient = MongoClients.create("mongodb://localhost:27017")) {

            var database = mongoClient.getDatabase("testdb");

            MongoCollection<Document> collection = database.getCollection("cars");

            try (MongoCursor<Document> cur = collection.find().iterator()) {

                while (cur.hasNext()) {

                    var doc = cur.next();
                    var cars = new ArrayList<>(doc.values());

                    System.out.printf("%s: %s%n", cars.get(1), cars.get(2));
                }
            }
        }
    }
}

In the example, we iterate over all data of the cars collection.

MongoCollection<Document> collection = database.getCollection("cars");

We retrieve the cars collection with the getCollection method.

try (MongoCursor<Document> cur = collection.find().iterator()) {

    while (cur.hasNext()) {

        var doc = cur.next();
        var cars = new ArrayList<>(doc.values());

        System.out.printf("%s: %s%n", cars.get(1), cars.get(2));
    }
}

We iterate through the documents of the collection. The find method finds all documents in the collection.

Audi: 52642.0
Mercedes: 57127.0
Skoda: 9000.0
Volvo: 29000.0
Bentley: 350000.0
Citroen: 21000.0
Hummer: 41400.0
Volkswagen: 21600.0

Java MongoDB query operators

It is possible to filter the data using MongoDB query operators such as $gt, $lt, or $ne. The query operators can be specified in the BasicDBObject class.

package com.zetcode;

import com.mongodb.BasicDBObject;
import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoCollection;
import org.bson.Document;

import java.util.function.Consumer;

public class MongoReadGreaterThan {

    public static void main(String[] args) {

        try (var mongoClient = MongoClients.create("mongodb://localhost:27017")) {

            var database = mongoClient.getDatabase("testdb");

            MongoCollection<Document> collection = database.getCollection("cars");

            var query = new BasicDBObject("price",
                    new BasicDBObject("$gt", 30000));

            collection.find(query).forEach((Consumer<Document>) doc ->
                     System.out.println(doc.toJson()));
        }
    }
}

The example prints all documents whose car prices' are greater than 30,000.

var query = new BasicDBObject("price",
    new BasicDBObject("$gt", 30000));

We use the $gt query operator.

collection.find(query).forEach((Consumer<Document>) doc ->
    System.out.println(doc.toJson()));

The forEach method is a syntactic sugar to avoid the need for the application code to worry about having to close the cursor manually. The data is printed in the JSON format using the toJson method.

{"_id": {"$oid": "5d4d13d6463315268eb7376b"}, "name": "Audi", "price": 52642.0}
{"_id": {"$oid": "5d4d13f5463315268eb7376c"}, "name": "Mercedes", "price": 57127.0}
{"_id": {"$oid": "5d4d140d463315268eb7376f"}, "name": "Bentley", "price": 350000.0}
{"_id": {"$oid": "5d4d1415463315268eb73771"}, "name": "Hummer", "price": 41400.0}

This is the output of the example in the JSON format. Only cars more expensive than 30,000 are included.

Java MongoDB factory filter query methods

The Java MongoDB driver contains factory methods for query filters.

package com.zetcode;

import com.mongodb.client.FindIterable;
import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import org.bson.Document;

import java.util.ArrayList;

import static com.mongodb.client.model.Filters.and;
import static com.mongodb.client.model.Filters.gt;
import static com.mongodb.client.model.Filters.lt;

public class MongoFilter {

    public static void main(String[] args) {

        try (var mongoClient = MongoClients.create("mongodb://localhost:27017")) {

            var database = mongoClient.getDatabase("testdb");

            MongoCollection<Document> collection = database.getCollection("cars");

            FindIterable fit = collection.find(and(lt("price", 50000),
                    gt("price", 20000))).sort(new Document("price", -1));

            var docs = new ArrayList<Document>();

            fit.into(docs);

            for (Document doc : docs) {

                System.out.println(doc);
            }
        }
    }
}

In the example, we retrieve cars whose prices fall between 20,000 and 50,000.

FindIterable fit = collection.find(and(lt("price", 50000),
    gt("price", 20000))).sort(new Document("price", -1));

The and, gt, and lt are factory filter methods. In addition, the data is sorted with the sort method.

Document{{_id=5d4d1415463315268eb73771, name=Hummer, price=41400.0}}
Document{{_id=5d4d1408463315268eb7376e, name=Volvo, price=29000.0}}
Document{{_id=5d4d1419463315268eb73772, name=Volkswagen, price=21600.0}}
Document{{_id=5d4d1411463315268eb73770, name=Citroen, price=21000.0}}

Java MongoDB projections

The Projections class provides static factory methods for all the MongoDB projection operators. By default, all fields of each document are projected. We can use the include and exclude methods to determine which fields should be projected into our output.

package com.zetcode;

import com.mongodb.client.FindIterable;
import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoCollection;
import org.bson.Document;

import java.util.ArrayList;

import static com.mongodb.client.model.Projections.excludeId;

public class MongoProjection {

    public static void main(String[] args) {

        try (var mongoClient = MongoClients.create("mongodb://localhost:27017")) {

            var database = mongoClient.getDatabase("testdb");

            MongoCollection<Document> collection = database.getCollection("cars");

            FindIterable it = collection.find().projection(excludeId());

            var docs = new ArrayList<Document>();

            it.into(docs);

            for (Document doc : docs) {

                System.out.println(doc);
            }
        }
    }
}

The example excludes the _id field from the output.

FindIterable it = collection.find().projection(excludeId());

The projection method sets a document describing the fields to return for all matching documents. The excludeId is a synonym for exclude("_id").

Document{{name=Audi, price=52642.0}}
Document{{name=Mercedes, price=57127.0}}
Document{{name=Skoda, price=9000.0}}
Document{{name=Volvo, price=29000.0}}
Document{{name=Bentley, price=350000.0}}
Document{{name=Citroen, price=21000.0}}
Document{{name=Hummer, price=41400.0}}
Document{{name=Volkswagen, price=21600.0}}

Java MongoDB limit data output

The limit query option specifies the number of documents to be returned and the skip option skips the specified number of documents.

package com.zetcode;

import com.mongodb.client.FindIterable;
import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoCollection;
import org.bson.Document;

import java.util.function.Consumer;

public class MongoSkipLimit {

    public static void main(String[] args) {

        try (var mongoClient = MongoClients.create("mongodb://localhost:27017")) {

            var database = mongoClient.getDatabase("testdb");

            MongoCollection<Document> collection = database.getCollection("cars");
            FindIterable<Document> fit = collection.find().skip(2).limit(5);

            fit.forEach((Consumer<Document>) System.out::println);
        }
    }
}

The example reads from the testdb.cars collection, skips the first two documents, and limits the output to five documents.

FindIterable<Document> fit = collection.find().skip(2).limit(5);

The FindIterable's skip method skips the first two documents and the limit method limits the output to five documents.

fit.forEach((Consumer<Document>) System.out::println);

Here we use Java 8 construct to print the documents.

Document{{_id=5d4d13fb463315268eb7376d, name=Skoda, price=9000.0}}
Document{{_id=5d4d1408463315268eb7376e, name=Volvo, price=29000.0}}
Document{{_id=5d4d140d463315268eb7376f, name=Bentley, price=350000.0}}
Document{{_id=5d4d1411463315268eb73770, name=Citroen, price=21000.0}}
Document{{_id=5d4d1415463315268eb73771, name=Hummer, price=41400.0}}

Java MongoDB create collection

The MongoDatabase's createCollection method creates a new collection in the database. The MongoCollection's insertMany method inserts one or more documents into the collection.

package com.zetcode;

import com.mongodb.MongoCommandException;
import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoCollection;
import org.bson.Document;

import java.util.ArrayList;

public class MongoCreateCollection {

    public static void main(String[] args) {

        try (var mongoClient = MongoClients.create("mongodb://localhost:27017")) {

            var database = mongoClient.getDatabase("testdb");

            try {

                database.createCollection("cars");
            } catch (MongoCommandException e) {

                database.getCollection("cars").drop();
            }

            var docs = new ArrayList<Document>();

            MongoCollection<Document> collection = database.getCollection("cars");

            var d1 = new Document("_id", 1);
            d1.append("name", "Audi");
            d1.append("price", 52642);
            docs.add(d1);

            var d2 = new Document("_id", 2);
            d2.append("name", "Mercedes");
            d2.append("price", 57127);
            docs.add(d2);

            var d3 = new Document("_id", 3);
            d3.append("name", "Skoda");
            d3.append("price", 9000);
            docs.add(d3);

            var d4 = new Document("_id", 4);
            d4.append("name", "Volvo");
            d4.append("price", 29000);
            docs.add(d4);

            var d5 = new Document("_id", 5);
            d5.append("name", "Bentley");
            d5.append("price", 350000);
            docs.add(d5);

            var d6 = new Document("_id", 6);
            d6.append("name", "Citroen");
            d6.append("price", 21000);
            docs.add(d6);

            var d7 = new Document("_id", 7);
            d7.append("name", "Hummer");
            d7.append("price", 41400);
            docs.add(d7);

            var d8 = new Document("_id", 8);
            d8.append("name", "Volkswagen");
            d8.append("price", 21600);
            docs.add(d8);

            collection.insertMany(docs);
        }
    }
}

The example creates a cars collection and inserts nine documents into it.

try {

    database.createCollection("cars");
} catch (MongoCommandException e) {

    database.getCollection("cars").drop();
}

A new collection is created with the createCollection method. If the collection already exists, it is dropped.

MongoCollection<Document> collection = database.getCollection("cars");

A MongoCollection of documents is created with the getCollection method.

var d1 = new Document("_id", 1);
d1.append("name", "Audi");
d1.append("price", 52642);
docs.add(d1);

A new Document is created. It contains the information about the car—its ID, name, and price.

collection.insertMany(docs);

The documents are written to the collection with the insertMany method.

Java MongoDB create collection from JSON

The JSON class has methods for parsing JSON documents. JSON (JavaScript Object Notation) is a lightweight data-interchange format. It is easy for humans to read and write.

package com.zetcode;

import com.mongodb.BasicDBObject;
import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoCollection;
import org.bson.Document;
import org.bson.types.ObjectId;

public class MongoCollectionFromJSON {

    public static void main(String[] args) {

        try (var mongoClient = MongoClients.create("mongodb://localhost:27017")) {

            var database = mongoClient.getDatabase("testdb");

            MongoCollection<Document> collection = database.getCollection("continents");

            var africa = BasicDBObject.parse("{_id : '" + ObjectId.get() + "', name : 'Africa'}");
            var asia = BasicDBObject.parse("{_id : '" + ObjectId.get() + "', name : 'Asia'}");
            var europe = BasicDBObject.parse("{_id : '" + ObjectId.get() + "', name : 'Europe'}");
            var america = BasicDBObject.parse("{_id : '" + ObjectId.get() + "', name : 'America'}");
            var australia = BasicDBObject.parse("{_id : '" + ObjectId.get() + "', name : 'Australia'}");
            var antarctica = BasicDBObject.parse("{_id : '" + ObjectId.get() + "', name : 'Antarctica'}");

            collection.insertOne(new Document(africa));
            collection.insertOne(new Document(asia));
            collection.insertOne(new Document(europe));
            collection.insertOne(new Document(america));
            collection.insertOne(new Document(australia));
            collection.insertOne(new Document(antarctica));
        }
    }
}

The example creates a continents collection from JSON data.

var africa = BasicDBObject.parse("{_id : '" + ObjectId.get() + "', name : 'Africa'}");

JSON data is parsed with the BasicDBObject.parse method.

collection.insertOne(new Document(africa));

The BasicDBObject is passed to Document and inserted into the collection with the insertOne method.

> db.continents.find()
{ "_id" : "5d4af89645ffb636567b6448", "name" : "Africa" }
{ "_id" : "5d4af89645ffb636567b6449", "name" : "Asia" }
{ "_id" : "5d4af89645ffb636567b644a", "name" : "Europe" }
{ "_id" : "5d4af89645ffb636567b644b", "name" : "America" }
{ "_id" : "5d4af89645ffb636567b644c", "name" : "Australia" }
{ "_id" : "5d4af89645ffb636567b644d", "name" : "Antarctica" }

We show the created collection with mongo.

Java MongoDB modify documents

The MongoCollection's deleteOne method is used to delete a document and updateOne to update a document.

package com.zetcode;

import com.mongodb.MongoClient;
import com.mongodb.client.MongoCollection;
import org.bson.Document;

import static com.mongodb.client.model.Filters.eq;

public class MongoModify {

    public static void main(String[] args) {

        try (var mongoClient = new MongoClient("localhost", 27017)) {

            var database = mongoClient.getDatabase("testdb");

            MongoCollection<Document> collection = database.getCollection("cars");

            collection.deleteOne(eq("name", "Skoda"));
            collection.updateOne(new Document("name", "Audi"),
                    new Document("$set", new Document("price", 52000)));

        }
    }
}

The example deletes a document containing Skoda and updates the price of Audi.

collection.deleteOne(eq("name", "Skoda"));

The deleteOne deletes the document of Skoda. The eq creates a filter that matches all documents where the value of the field name equals the specified value.

collection.updateOne(new Document("name", "Audi"),
    new Document("$set", new Document("price", 52000)));

The price of Audi is changed to 52,000 with the updateOne method.

> db.cars.find()
{ "_id" : ObjectId("5d4d13d6463315268eb7376b"), "name" : "Audi", "price" : 52000 }
{ "_id" : ObjectId("5d4d13f5463315268eb7376c"), "name" : "Mercedes", "price" : 57127 }
{ "_id" : ObjectId("5d4d1408463315268eb7376e"), "name" : "Volvo", "price" : 29000 }
{ "_id" : ObjectId("5d4d140d463315268eb7376f"), "name" : "Bentley", "price" : 350000 }
{ "_id" : ObjectId("5d4d1411463315268eb73770"), "name" : "Citroen", "price" : 21000 }
{ "_id" : ObjectId("5d4d1415463315268eb73771"), "name" : "Hummer", "price" : 41400 }
{ "_id" : ObjectId("5d4d1419463315268eb73772"), "name" : "Volkswagen", "price" : 21600 }

We confirm the changes with the mongo tool.

Source

MongoDB Java documentation

In this article we have worked with MongoDB and Java.

Author

My name is Jan Bodnar and I am a passionate programmer with many years of programming experience. I have been writing programming articles since 2007. So far, I have written over 1400 articles and 8 e-books. I have over eight years of experience in teaching programming.

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