POJO to org.bson.Document and Vice Versa

You can use Gson and Document.parse(String json) to convert a POJO to a Document. This works with the version 3.4.2 of java driver.

Something like this:

package com.jacobcs;

import org.bson.Document;

import com.google.gson.Gson;
import com.mongodb.MongoClient;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;

public class MongoLabs {

    public static void main(String[] args) {
        // create client and connect to db
        MongoClient mongoClient = new MongoClient("localhost", 27017);
        MongoDatabase database = mongoClient.getDatabase("my_db_name");

        // populate pojo
        MyPOJO myPOJO = new MyPOJO();
        myPOJO.setName("MyName");
        myPOJO.setAge("26");

        // convert pojo to json using Gson and parse using Document.parse()
        Gson gson = new Gson();
        MongoCollection<Document> collection = database.getCollection("my_collection_name");
        Document document = Document.parse(gson.toJson(myPOJO));
        collection.insertOne(document);
    }

}

Currently Mongo Java Driver 3.9.1 provide POJO support out of the box
http://mongodb.github.io/mongo-java-driver/3.9/driver/getting-started/quick-start-pojo/
Let's say you have such example collection with one nested object

db.createCollection("product", {
validator: {
    $jsonSchema: {
        bsonType: "object",
        required: ["name", "description", "thumb"],
        properties: {
            name: {
                bsonType: "string",
                description: "product - name - string"
            },
            description: {
                bsonType: "string",
                description: "product - description - string"
            },
            thumb: {
                bsonType: "object",
                required: ["width", "height", "url"],
                properties: {
                    width: {
                        bsonType: "int",
                        description: "product - thumb - width"
                    },
                    height: {
                        bsonType: "int",
                        description: "product - thumb - height"
                    },
                    url: {
                        bsonType: "string",
                        description: "product - thumb - url"
                    }
                }
            }

        }
    }
}});

1. Provide a MongoDatabase bean with proper CodecRegistry

@Bean
public MongoClient mongoClient() {
    ConnectionString connectionString = new ConnectionString("mongodb://username:[email protected]:27017/dbname");

    ConnectionPoolSettings connectionPoolSettings = ConnectionPoolSettings.builder()
            .minSize(2)
            .maxSize(20)
            .maxWaitQueueSize(100)
            .maxConnectionIdleTime(60, TimeUnit.SECONDS)
            .maxConnectionLifeTime(300, TimeUnit.SECONDS)
            .build();

    SocketSettings socketSettings = SocketSettings.builder()
            .connectTimeout(5, TimeUnit.SECONDS)
            .readTimeout(5, TimeUnit.SECONDS)
            .build();

    MongoClientSettings clientSettings = MongoClientSettings.builder()
            .applyConnectionString(connectionString)
            .applyToConnectionPoolSettings(builder -> builder.applySettings(connectionPoolSettings))
            .applyToSocketSettings(builder -> builder.applySettings(socketSettings))
            .build();

    return MongoClients.create(clientSettings);
}

@Bean 
public MongoDatabase mongoDatabase(MongoClient mongoClient) {
    CodecRegistry defaultCodecRegistry = MongoClientSettings.getDefaultCodecRegistry();
    CodecRegistry fromProvider = CodecRegistries.fromProviders(PojoCodecProvider.builder().automatic(true).build());
    CodecRegistry pojoCodecRegistry = CodecRegistries.fromRegistries(defaultCodecRegistry, fromProvider);
    return mongoClient.getDatabase("dbname").withCodecRegistry(pojoCodecRegistry);
}

2. Annotate your POJOS

public class ProductEntity {

    @BsonProperty("name") public final String name;
    @BsonProperty("description") public final String description;
    @BsonProperty("thumb") public final ThumbEntity thumbEntity;

    @BsonCreator
    public ProductEntity(
            @BsonProperty("name") String name,
            @BsonProperty("description") String description,
            @BsonProperty("thumb") ThumbEntity thumbEntity) {
        this.name = name;
        this.description = description;
        this.thumbEntity = thumbEntity;
    }
}

public class ThumbEntity {

    @BsonProperty("width") public final Integer width;
    @BsonProperty("height") public final Integer height;
    @BsonProperty("url") public final String url;

    @BsonCreator
    public ThumbEntity(
            @BsonProperty("width") Integer width,
            @BsonProperty("height") Integer height,
            @BsonProperty("url") String url) {
        this.width = width;
        this.height = height;
        this.url = url;
    }
}

3. Query mongoDB and obtain POJOS

MongoCollection<Document> collection = mongoDatabase.getCollection("product");
Document query = new Document();
List<ProductEntity> products = collection.find(query, ProductEntity.class).into(new ArrayList<>());

And that's it !!! You can easily obtain your POJOS without cumbersome manual mappings and without loosing ability to run native mongo queries

The point is, that you do not need to put your hands on org.bson.Document.

Morphia will do all that for you behind the curtain.

import com.mongodb.MongoClient;
import org.mongodb.morphia.Datastore;
import org.mongodb.morphia.DatastoreImpl;
import org.mongodb.morphia.Morphia;
import java.net.UnknownHostException;

.....
    private Datastore createDataStore() throws UnknownHostException {
        MongoClient client = new MongoClient("localhost", 27017);
        // create morphia and map classes
        Morphia morphia = new Morphia();
        morphia.map(FooBar.class);
        return new DatastoreImpl(morphia, client, "testmongo");
    }

......

    //with the Datastore from above you can save any mapped class to mongo
    Datastore datastore;
    final FooBar fb = new FooBar("hello", "world");
    datastore.save(fb);

Here you will find several examples: https://mongodb.github.io/morphia/