Java MongoDB CRUD Operations

In this tutorial, you will learn how to perform basic CRUD (Create, Read, Update, Delete) operations on a MongoDB collection using Java. We'll use the MongoDB Java Driver to connect to MongoDB and demonstrate these four operations with code examples.

What You Will Learn:

• How to connect Java to MongoDB.
• How to perform Create, Read, Update, and Delete operations in MongoDB using Java.
• How to verify each operation in MongoDB.

Technologies Used:

• JDK: Version 21
• MongoDB: Version 6.0 or later
• MongoDB Java Driver: Version 5.1.4

Step 1: Add MongoDB Java Driver Dependency

To perform CRUD operations, add the MongoDB Java Driver to your project.

For Maven Users:

Add the following dependency to your pom.xml file:

<dependency>
    <groupId>org.mongodb</groupId>
    <artifactId>mongodb-driver-sync</artifactId>
    <version>5.1.4</version>
</dependency>

For Gradle Users:

Add the following line to your build.gradle file:

implementation 'org.mongodb:mongodb-driver-sync:5.1.4'

If you don't use Maven or Gradle, you can download the MongoDB Java Driver JAR file and manually add it to your classpath.

Step 2: Connect to MongoDB

First, establish a connection to your MongoDB database.

Code Example:

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

public class MongoDBConnectionExample {
    
    private static final String URI = "mongodb://localhost:27017";
    
    public static void main(String[] args) {
        // Connect to MongoDB server
        try (MongoClient mongoClient = MongoClients.create(URI)) {
            
            // Access the database
            MongoDatabase database = mongoClient.getDatabase("mydb");
            
            System.out.println("Connected to MongoDB database: " + database.getName());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Explanation:

• The MongoClient establishes the connection to MongoDB.
• The getDatabase("mydb") method accesses or creates a database named mydb.

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Step 3: Create (Insert a Document)

Let’s insert a document into a collection named employees.

Code Example:

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

public class MongoDBCreateExample {

    public static void main(String[] args) {
        try (MongoClient mongoClient = MongoClients.create(URI)) {
            
            MongoDatabase database = mongoClient.getDatabase("mydb");
            MongoCollection<Document> collection = database.getCollection("employees");

            // Create a new document
            Document employee = new Document("name", "Raj")
                                .append("age", 30)
                                .append("department", "IT");
            
            // Insert the document
            collection.insertOne(employee);
            
            System.out.println("Document inserted: " + employee.toJson());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Explanation:

• Document represents the data to insert.
• insertOne() inserts the document into the employees collection.

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Step 4: Read (Retrieve Documents)

Now, let's retrieve the documents from the employees collection.

Code Example:

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

public class MongoDBReadExample {

    public static void main(String[] args) {
        try (MongoClient mongoClient = MongoClients.create(URI)) {
            
            MongoDatabase database = mongoClient.getDatabase("mydb");
            MongoCollection<Document> collection = database.getCollection("employees");

            // Fetch all documents from the collection
            MongoCursor<Document> cursor = collection.find().iterator();
            
            // Iterate and print each document
            while (cursor.hasNext()) {
                System.out.println(cursor.next().toJson());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Explanation:

• collection.find() fetches all documents from the employees collection.
• The MongoCursor iterates through the documents and prints them.

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Step 5: Update (Modify a Document)

Next, we update the department of an employee whose name is "Raj".

Code Example:

import com.mongodb.client.model.Filters;
import com.mongodb.client.model.Updates;

public class MongoDBUpdateExample {

    public static void main(String[] args) {
        try (MongoClient mongoClient = MongoClients.create(URI)) {
            
            MongoDatabase database = mongoClient.getDatabase("mydb");
            MongoCollection<Document> collection = database.getCollection("employees");

            // Update the department of an employee with name "Raj"
            collection.updateOne(Filters.eq("name", "Raj"),
                                 Updates.set("department", "Engineering"));
            
            System.out.println("Document updated successfully.");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Explanation:

• Filters.eq() is used to find documents where name = "Raj".
• Updates.set() modifies the department field for the matching document.

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Step 6: Delete (Remove a Document)

Finally, let’s delete an employee document named "Raj".

Code Example:

import com.mongodb.client.result.DeleteResult;
import com.mongodb.client.model.Filters;

public class MongoDBDeleteExample {

    public static void main(String[] args) {
        try (MongoClient mongoClient = MongoClients.create(URI)) {
            
            MongoDatabase database = mongoClient.getDatabase("mydb");
            MongoCollection<Document> collection = database.getCollection("employees");

            // Delete the document where the name is "Raj"
            DeleteResult result = collection.deleteOne(Filters.eq("name", "Raj"));
            
            if (result.getDeletedCount() > 0) {
                System.out.println("Document deleted successfully.");
            } else {
                System.out.println("No document found with the specified criteria.");
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Explanation:

• deleteOne() deletes the first document that matches the filter condition.
• Filters.eq("name", "Raj") identifies the document to delete.

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Step 7: Run and Test Each CRUD Operation

You can run each example as a standalone Java program or integrate all operations in one project. Use the MongoDB shell or a MongoDB client tool to verify the changes in the employees collection.

Shell Verification:

use mydb
db.employees.find()

Conclusion

In this tutorial, you learned how to:

• Connect Java 21 to MongoDB using the MongoDB Java Driver.
• Perform CRUD operations (Create, Read, Update, Delete) on a MongoDB collection.
• Verify the CRUD operations using the MongoDB shell.

This is a basic guide to performing essential MongoDB operations using Java. You can extend it by adding more advanced query filters, handling bulk operations, and implementing transactional operations.