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In this section, we will explore how to integrate MongoDB with Java. We will cover the following topics:

Setting up the MongoDB Java Driver
Connecting to MongoDB
Performing CRUD Operations
Using Aggregation Framework
Practical Exercises

Setting up the MongoDB Java Driver

To interact with MongoDB from a Java application, you need to include the MongoDB Java Driver in your project. We will use Maven for dependency management.

Maven Dependency

Add the following dependency to your pom.xml file:

<dependency>
    <groupId>org.mongodb</groupId>
    <artifactId>mongodb-driver-sync</artifactId>
    <version>4.4.0</version>
</dependency>

Gradle Dependency

If you are using Gradle, add the following to your build.gradle file:

implementation 'org.mongodb:mongodb-driver-sync:4.4.0'

Connecting to MongoDB

To connect to a MongoDB instance, you need to create a MongoClient object. Here is an example of how to connect to a local MongoDB instance:

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

public class MongoDBConnection {
    public static void main(String[] args) {
        // Create a MongoClient object
        MongoClient mongoClient = MongoClients.create("mongodb://localhost:27017");

        // Access the database
        MongoDatabase database = mongoClient.getDatabase("mydatabase");

        System.out.println("Connected to the database successfully");
    }
}

Explanation

MongoClients.create("mongodb://localhost:27017"): Creates a new MongoClient instance connected to the MongoDB server running on localhost at port 27017.
mongoClient.getDatabase("mydatabase"): Accesses the database named mydatabase.

Performing CRUD Operations

Creating Documents

To insert a document into a collection, use the insertOne method.

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

public class CreateDocument {
    public static void main(String[] args) {
        MongoClient mongoClient = MongoClients.create("mongodb://localhost:27017");
        MongoDatabase database = mongoClient.getDatabase("mydatabase");
        MongoCollection<Document> collection = database.getCollection("mycollection");

        Document document = new Document("name", "John Doe")
                .append("age", 30)
                .append("city", "New York");

        collection.insertOne(document);
        System.out.println("Document inserted successfully");
    }
}

Reading Documents

To read documents from a collection, use the find method.

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

public class ReadDocuments {
    public static void main(String[] args) {
        MongoClient mongoClient = MongoClients.create("mongodb://localhost:27017");
        MongoDatabase database = mongoClient.getDatabase("mydatabase");
        MongoCollection<Document> collection = database.getCollection("mycollection");

        FindIterable<Document> documents = collection.find();
        for (Document doc : documents) {
            System.out.println(doc.toJson());
        }
    }
}

Updating Documents

To update a document, use the updateOne method.

import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import org.bson.Document;
import com.mongodb.client.model.Filters;
import com.mongodb.client.model.Updates;

public class UpdateDocument {
    public static void main(String[] args) {
        MongoClient mongoClient = MongoClients.create("mongodb://localhost:27017");
        MongoDatabase database = mongoClient.getDatabase("mydatabase");
        MongoCollection<Document> collection = database.getCollection("mycollection");

        collection.updateOne(Filters.eq("name", "John Doe"), Updates.set("age", 31));
        System.out.println("Document updated successfully");
    }
}

Deleting Documents

To delete a document, use the deleteOne method.

import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import org.bson.Document;
import com.mongodb.client.model.Filters;

public class DeleteDocument {
    public static void main(String[] args) {
        MongoClient mongoClient = MongoClients.create("mongodb://localhost:27017");
        MongoDatabase database = mongoClient.getDatabase("mydatabase");
        MongoCollection<Document> collection = database.getCollection("mycollection");

        collection.deleteOne(Filters.eq("name", "John Doe"));
        System.out.println("Document deleted successfully");
    }
}

Using Aggregation Framework

The aggregation framework allows you to perform complex data processing and transformation operations.

import com.mongodb.client.AggregateIterable;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import org.bson.Document;

import java.util.Arrays;

public class AggregationExample {
    public static void main(String[] args) {
        MongoClient mongoClient = MongoClients.create("mongodb://localhost:27017");
        MongoDatabase database = mongoClient.getDatabase("mydatabase");
        MongoCollection<Document> collection = database.getCollection("mycollection");

        AggregateIterable<Document> result = collection.aggregate(Arrays.asList(
                new Document("$match", new Document("city", "New York")),
                new Document("$group", new Document("_id", "$city")
                        .append("averageAge", new Document("$avg", "$age")))
        ));

        for (Document doc : result) {
            System.out.println(doc.toJson());
        }
    }
}

Explanation

$match: Filters documents to include only those where the city is "New York".
$group: Groups the documents by city and calculates the average age.

Practical Exercises

Exercise 1: Insert Multiple Documents

Write a Java program to insert multiple documents into a MongoDB collection.

Solution:

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

import java.util.Arrays;

public class InsertMultipleDocuments {
    public static void main(String[] args) {
        MongoClient mongoClient = MongoClients.create("mongodb://localhost:27017");
        MongoDatabase database = mongoClient.getDatabase("mydatabase");
        MongoCollection<Document> collection = database.getCollection("mycollection");

        Document doc1 = new Document("name", "Alice").append("age", 25).append("city", "Los Angeles");
        Document doc2 = new Document("name", "Bob").append("age", 28).append("city", "Chicago");

        collection.insertMany(Arrays.asList(doc1, doc2));
        System.out.println("Documents inserted successfully");
    }
}

Exercise 2: Find Documents with a Specific Condition

Write a Java program to find all documents where the age is greater than 25.

Solution:

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

public class FindDocuments {
    public static void main(String[] args) {
        MongoClient mongoClient = MongoClients.create("mongodb://localhost:27017");
        MongoDatabase database = mongoClient.getDatabase("mydatabase");
        MongoCollection<Document> collection = database.getCollection("mycollection");

        FindIterable<Document> documents = collection.find(Filters.gt("age", 25));
        for (Document doc : documents) {
            System.out.println(doc.toJson());
        }
    }
}

Conclusion

In this section, we covered how to set up the MongoDB Java Driver, connect to a MongoDB instance, and perform CRUD operations. We also explored the aggregation framework and provided practical exercises to reinforce the learned concepts. In the next module, we will delve into building real-world applications using MongoDB.

MongoDB with Java

Setting up the MongoDB Java Driver

Maven Dependency

Gradle Dependency

Connecting to MongoDB

Explanation

Performing CRUD Operations

Creating Documents

Reading Documents

Updating Documents

Deleting Documents

Using Aggregation Framework

Explanation

Practical Exercises

Exercise 1: Insert Multiple Documents

Exercise 2: Find Documents with a Specific Condition

Conclusion

MongoDB Course

Module 1: Introduction to MongoDB

Module 2: MongoDB CRUD Operations

Module 3: Data Modeling in MongoDB

Module 4: Indexing and Aggregation

Module 5: Advanced MongoDB Features

Module 6: Performance and Security

Module 7: MongoDB with Programming Languages

Module 8: Real-World Applications