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

spring.data.mongodb.uri=mongodb://localhost:27017/springboot-db

spring.data.mongodb.uri=mongodb://name:pass@localhost:27017/dbname

package com.forezp.entity;

import org.springframework.data.annotation.Id;


public class Customer {

  @Id
  public String id;

  public String firstName;
  public String lastName;

  public Customer() {}

  public Customer(String firstName, String lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
  }

  @Override
  public String toString() {
    return String.format(
        "Customer[id=%s, firstName='%s', lastName='%s']",
        id, firstName, lastName);
  }

}

public interface CustomerRepository extends MongoRepository<Customer, String> {

  public Customer findByFirstName(String firstName);
  public List<Customer> findByLastName(String lastName);

}

@SpringBootApplication
public class SpringbootMongodbApplication implements CommandLineRunner {


  @Autowired
  private CustomerRepository repository;

  public static void main(String[] args) {
    SpringApplication.run(SpringbootMongodbApplication.class, args);
  }


  @Override
  public void run(String... args) throws Exception {
    repository.deleteAll();

    // save a couple of customers
    repository.save(new Customer("Alice", "Smith"));
    repository.save(new Customer("Bob", "Smith"));

    // fetch all customers
    System.out.println("Customers found with findAll():");
    System.out.println("-------------------------------");
    for (Customer customer : repository.findAll()) {
      System.out.println(customer);
    }
    System.out.println();

    // fetch an individual customer
    System.out.println("Customer found with findByFirstName('Alice'):");
    System.out.println("--------------------------------");
    System.out.println(repository.findByFirstName("Alice"));

    System.out.println("Customers found with findByLastName('Smith'):");
    System.out.println("--------------------------------");
    for (Customer customer : repository.findByLastName("Smith")) {
      System.out.println(customer);
    }
  }

Customers found with findAll(): 
——————————- 
Customer[id=58f880f589ffb696b8a6077e, firstName='Alice', lastName='Smith'] 
Customer[id=58f880f589ffb696b8a6077f, firstName='Bob', lastName='Smith'] 
Customer found with findByFirstName(‘Alice'): 
——————————– 
Customer[id=58f880f589ffb696b8a6077e, firstName='Alice', lastName='Smith'] 
Customers found with findByLastName(‘Smith'): 
——————————– 
Customer[id=58f880f589ffb696b8a6077e, firstName='Alice', lastName='Smith'] 
Customer[id=58f880f589ffb696b8a6077f, firstName='Bob', lastName='Smith']