This guide walks you through the process of using Spring Data MongoDB to build an application that stores data in and retrieves it from MongoDB, a document-based database.

What You Will build

You will store Customer POJOs (Plain Old Java Objecgs) in a MongoDB database by using Spring Data MongoDB.

What You Need

How to complete this guide

Like most Spring Getting Started guides, you can start from scratch and complete each step or you can bypass basic setup steps that are already familiar to you. Either way, you end up with working code.

To start from scratch, move on to Starting with Spring Initializr.

To skip the basics, do the following:

When you finish, you can check your results against the code in gs-accessing-data-mongodb/complete.

Starting with Spring Initializr

For all Spring applications, you should start with the Spring Initializr. The Initializr offers a fast way to pull in all the dependencies you need for an application and does a lot of the set up for you. This example needs only the Spring Data MongoDB dependency. The following image shows the Initializr set up for this sample project:

initializr
The preceding image shows the Initializr with Maven chosen as the build tool. You can also use Gradle. It also shows values of com.example and accessing-data-mongodb as the Group and Artifact, respectively. You will use those values throughout the rest of this sample.

The following listing shows the pom.xml file created when you choose Maven:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.1.7.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.example</groupId>
	<artifactId>accessing-data-mongodb</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>accessing-data-mongodb</name>
	<description>Demo project for Spring Boot</description>

	<properties>
		<java.version>1.8</java.version>
	</properties>

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

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

The following listing shows the build.gradle file created when you choose Gradle:

plugins {
	id 'org.springframework.boot' version '2.1.7.RELEASE'
	id 'io.spring.dependency-management' version '1.0.8.RELEASE'
	id 'java'
}

group = 'com.example'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '1.8'

repositories {
	mavenCentral()
}

dependencies {
	implementation 'org.springframework.boot:spring-boot-starter-data-mongodb'
	testImplementation 'org.springframework.boot:spring-boot-starter-test'
}

Install and Launch MongoDB

With your project set up, you can install and launch the MongoDB database.

If you use a Mac with Homebrew, you can run the following command:

$ brew install mongodb

With MacPorts, you can run the following command:

$ port install mongodb

For other systems with package management, such as Redhat, Ubuntu, Debian, CentOS, and Windows, see the instructions at https://docs.mongodb.org/manual/installation/.

After you install MongoDB, you can launch it in a console window by running the following command (which also starts up a server process):

$ mongod

You should see output similar to the following:

all output going to: /usr/local/var/log/mongodb/mongo.log

Define a Simple Entity

MongoDB is a NoSQL document store. In this example, you store Customer objects. The following listing shows the Customer class (in src/main/java/com/example/accessingdatamongodb/Customer.java):

package com.example.accessingdatamongodb;

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);
    }

}

Here you have a Customer class with three attributes: id, firstName, and lastName. The id is mostly for internal use by MongoDB. You also have a single constructor to populate the entities when creating a new instance.

In this guide, the typical getters and setters have been left out for brevity.

id fits the standard name for a MongoDB ID, so it does not require any special annotation to tag it for Spring Data MongoDB.

The other two properties, firstName and lastName, are left unannotated. It is assumed that they are mapped to fields that share the same name as the properties themselves.

The convenient toString() method prints out the details about a customer.

MongoDB stores data in collections. Spring Data MongoDB maps the Customer class into a collection called customer. If you want to change the name of the collection, you can use Spring Data MongoDB’s @Document annotation on the class.

Create Simple Queries

Spring Data MongoDB focuses on storing data in MongoDB. It also inherits functionality from the Spring Data Commons project, such as the ability to derive queries. Essentially, you need not learn the query language of MongoDB. You can write a handful of methods and the queries are written for you.

To see how this works, create a repository interface that queries Customer documents, as the following listing (in src/main/java/com/example/accessingdatamongodb/CustomerRepository.java) shows:

package com.example.accessingdatamongodb;

import java.util.List;

import org.springframework.data.mongodb.repository.MongoRepository;

public interface CustomerRepository extends MongoRepository<Customer, String> {

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

}

CustomerRepository extends the MongoRepository interface and plugs in the type of values and ID that it works with: Customer and String, respectively. This interface comes with many operations, including standard CRUD operations (create, read, update, and delete).

You can define other queries by declaring their method signatures. In this case, add findByFirstName, which essentially seeks documents of type Customer and finds the documents that match on firstName.

You also have findByLastName, which finds a list of people by last name.

In a typical Java application, you write a class that implements CustomerRepository and craft the queries yourself. What makes Spring Data MongoDB so useful is the fact that you need not create this implementation. Spring Data MongoDB creates it on the fly when you run the application.

Now you can wire up this application and see what it looks like!

Create an Application Class

Spring Initializr creates a simple class for the application. The following listing shows the class that Initializr created for this example (in src/main/java/com/example/accessingdatamongodb/AccessingDataMongodbApplication.java):

package com.example.accessingdatamongodb;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class AccessingDataMongodbApplication {

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

}

@SpringBootApplication is a convenience annotation that adds all of the following:

  • @Configuration: Tags the class as a source of bean definitions for the application context.

  • @EnableAutoConfiguration: Tells Spring Boot to start adding beans based on classpath settings, other beans, and various property settings. For example, if spring-webmvc is on the classpath, this annotation flags the application as a web application and activates key behaviors, such as setting up a DispatcherServlet.

  • @ComponentScan: Tells Spring to look for other components, configurations, and services in the com/example package, letting it find the controllers.

The main() method uses Spring Boot’s SpringApplication.run() method to launch an application. Did you notice that there was not a single line of XML? There is no web.xml file, either. This web application is 100% pure Java and you did not have to deal with configuring any plumbing or infrastructure.

Spring Boot automatically handles those repositories as long as they are included in the same package (or a sub-package) of your @SpringBootApplication class. For more control over the registration process, you can use the @EnableMongoRepositories annotation.

By default, @EnableMongoRepositories scans the current package for any interfaces that extend one of Spring Data’s repository interfaces. You can use its basePackageClasses=MyRepository.class to safely tell Spring Data MongoDB to scan a different root package by type if your project layout has multiple projects and it does not find your repositories.

Spring Data MongoDB uses the MongoTemplate to execute the queries behind your find* methods. You can use the template yourself for more complex queries, but this guide does not cover that. (see the Spring Data MongoDB Reference Guide)

Now you need to modify the simple class that the Initializr created for you. You need to set up some data and use it to generate output. The following listing shows the finished AccessingDataMongodbApplication class (in src/main/java/com/example/accessingdatamongodb/AccessingDataMongodbApplication.java):

package com.example.accessingdatamongodb;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class AccessingDataMongodbApplication implements CommandLineRunner {

	@Autowired
	private CustomerRepository repository;

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

	}

}

AccessingDataMongodbApplication includes a main() method that autowires an instance of CustomerRepository. Spring Data MongoDB dynamically creates a proxy and injects it there. We use the CustomerRepository through a few tests. First, it saves a handful of Customer objects, demonstrating the save() method and setting up some data to use. Next, it calls findAll() to fetch all Customer objects from the database. Then it calls findByFirstName() to fetch a single Customer by her first name. Finally, it calls findByLastName() to find all customers whose last name is Smith.

By default, Spring Boot tries to connect to a locally hosted instance of MongoDB. Read the reference docs for details on pointing your application to an instance of MongoDB hosted elsewhere.

Build an executable JAR

You can run the application from the command line with Gradle or Maven. You can also build a single executable JAR file that contains all the necessary dependencies, classes, and resources and run that. Building an executable jar so makes it easy to ship, version, and deploy the service as an application throughout the development lifecycle, across different environments, and so forth.

If you use Gradle, you can run the application by using ./gradlew bootRun. Alternatively, you can build the JAR file by using ./gradlew build and then run the JAR file, as follows:

java -jar build/libs/gs-accessing-data-mongodb-0.1.0.jar

If you use Maven, you can run the application by using ./mvnw spring-boot:run. Alternatively, you can build the JAR file with ./mvnw clean package and then run the JAR file, as follows:

java -jar target/gs-accessing-data-mongodb-0.1.0.jar
The steps described here create a runnable JAR. You can also build a classic WAR file.

As AccessingDataMongodbApplication implements CommandLineRunner, the run method is automatically invoked when Spring Boot starts. You should see something like the following (with other output, such as queries, as well):

== Customers found with findAll():
Customer[id=51df1b0a3004cb49c50210f8, firstName='Alice', lastName='Smith']
Customer[id=51df1b0a3004cb49c50210f9, firstName='Bob', lastName='Smith']

== Customer found with findByFirstName('Alice'):
Customer[id=51df1b0a3004cb49c50210f8, firstName='Alice', lastName='Smith']
== Customers found with findByLastName('Smith'):
Customer[id=51df1b0a3004cb49c50210f8, firstName='Alice', lastName='Smith']
Customer[id=51df1b0a3004cb49c50210f9, firstName='Bob', lastName='Smith']

Summary

Congratulations! You set up a MongoDB server and wrote a simple application that uses Spring Data MongoDB to save objects to and fetch them from a database, all without writing a concrete repository implementation.

If you want to expose MongoDB repositories with a hypermedia-based RESTful front end with little effort, read Accessing MongoDB Data with REST.

See Also

The following guides may also be helpful:

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All guides are released with an ASLv2 license for the code, and an Attribution, NoDerivatives creative commons license for the writing.