How to Seamlessly Integrate Spring Boot with MongoDB: A Step‑by‑Step Guide

This guide explains how to integrate MongoDB into a Spring Boot application, covering dependency setup, connection configuration, entity and repository creation, service and controller implementation, and optional sharding or replica‑set configurations.

1. Add Dependencies

<dependencies>
   <!-- MongoDB driver -->
   <dependency>
       <groupId>org.mongodb</groupId>
       <artifactId>mongodb-driver-sync</artifactId>
       <version>4.4.0</version>
   </dependency>
   <!-- Spring Data MongoDB -->
   <dependency>
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-starter-data-mongodb</artifactId>
       <version>2.6.2</version>
   </dependency>
</dependencies>

2. Configure MongoDB Connection

spring.data.mongodb.uri=mongodb://username:password@localhost:27017/myDatabase

3. Create Entity Class

import org.springframework.data.annotation.Id;
import org.springframework.data.mongodb.core.mapping.Document;

@Document(collection = "users")
public class User {
    @Id
    private String id;
    private String name;
    private int age;
    // Getters and setters
}

4. Create Repository Interface

import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface UserRepository extends CrudRepository<User, String> {
}

5. Service Layer Using Repository

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class UserService {
    @Autowired
    private UserRepository userRepository;

    public User save(User user) {
        return userRepository.save(user);
    }

    public User findById(String id) {
        return userRepository.findById(id).orElse(null);
    }
    // Other CRUD methods
}

6. Controller Layer Handling HTTP Requests

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping("/users")
public class UserController {
    @Autowired
    private UserService userService;

    @PostMapping
    public User save(@RequestBody User user) {
        return userService.save(user);
    }

    @GetMapping("/{id}")
    public User findById(@PathVariable String id) {
        return userService.findById(id);
    }
}

7. Optional: Sharding Configuration

Sharding distributes collections across multiple servers to improve performance. Add sharding properties in application.properties or application.yml and create a configuration class.

spring.data.mongodb.shard-strategy=org.springframework.data.mongodb.core.shard.BackwardCompatibleShardingStrategy
spring.data.mongodb.target-db-config.default.mongo-uri=mongodb://localhost:27017/mydb
spring.data.mongodb.target-db-config.default.database=mydb
spring.data.mongodb.target-db-config.shard-targets={"ds"=>0,"target"=>"mydb_${0..199}"}

@Configuration
public class MongoDBConfiguration {
    @Bean
    public ShardingDataSource shardingDataSource() {
        // Create a sharding data source
        // ...
    }

    @Bean
    public MongoDatabaseFactory mongoDatabaseFactory() {
        // Create a MongoDatabaseFactory instance
        // ...
    }
}

8. Optional: Replica Set Configuration

Replica sets provide data redundancy and read/write scaling. Define replica‑set properties and a configuration class.

spring.data.mongodb.replica-set=myReplicaSet
spring.data.mongodb.host=mongodb://localhost:27017
spring.data.mongodb.port=27017
spring.data.mongodb.authentication-database=admin
spring.data.mongodb.database=mydb

@Configuration
public class MongoDBConfiguration {
    @Bean
    public MongoClient mongoClient() {
        // Create a MongoClient instance
        // ...
    }
}

Ensure the MongoDB service is running, entity fields match database fields, and the appropriate Spring Data MongoDB dependencies are included in pom.xml:

<dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-data-mongodb</artifactId>
</dependency>

With these steps, a basic Spring Boot application can interact with MongoDB, and you can extend it with sharding or replica‑set features as needed.