mn create-app example.micronaut.micronautguide \
--features=yaml,mongo-reactive,reactor,graalvm,serialization-bson,serialization-jackson \
--build=maven \
--lang=java \
--test=junit
Table of Contents
Micronaut MongoDB Asynchronous
Learn how to use a non-blocking reactive streams MongoDB client with a Micronaut application
Authors: Sergio del Amo
Micronaut Version: 4.6.1
1. Getting Started
In this guide, we will create a Micronaut application written in Java.
You will use MongoDB for persistence.
2. What you will need
To complete this guide, you will need the following:
-
Some time on your hands
-
A decent text editor or IDE (e.g. IntelliJ IDEA)
-
JDK 17 or greater installed with
JAVA_HOME
configured appropriately
3. Solution
We recommend that you follow the instructions in the next sections and create the application step by step. However, you can go right to the completed example.
-
Download and unzip the source
4. Writing the Application
Create an application using the Micronaut Command Line Interface or with Micronaut Launch.
If you don’t specify the --build argument, Gradle is used as the build tool. If you don’t specify the --lang argument, Java is used as the language.If you don’t specify the --test argument, JUnit is used for Java and Kotlin, and Spock is used for Groovy.
|
The previous command creates a Micronaut application with the default package example.micronaut
in a directory named micronautguide
.
If you use Micronaut Launch, select Micronaut Application as application type and add yaml
, mongo-reactive
, reactor
, graalvm
, serialization-bson
, and serialization-jackson
features.
If you have an existing Micronaut application and want to add the functionality described here, you can view the dependency and configuration changes from the specified features and apply those changes to your application. |
4.1. POJO
Create Fruit
POJO:
package example.micronaut;
import io.micronaut.core.annotation.Creator;
import io.micronaut.core.annotation.NonNull;
import io.micronaut.core.annotation.Nullable;
import io.micronaut.serde.annotation.Serdeable;
import org.bson.codecs.pojo.annotations.BsonCreator;
import org.bson.codecs.pojo.annotations.BsonProperty;
import jakarta.validation.constraints.NotBlank;
@Serdeable (1)
public class Fruit {
@NonNull
@NotBlank (2)
@BsonProperty("name") (3)
private final String name;
@Nullable
@BsonProperty("description") (3)
private final String description;
public Fruit(@NonNull String name) {
this(name, null);
}
@Creator (4)
@BsonCreator(3)
public Fruit(@NonNull @BsonProperty("name") String name, (3)
@Nullable @BsonProperty("description") String description) { (3)
this.name = name;
this.description = description;
}
@NonNull
public String getName() {
return name;
}
@Nullable
public String getDescription() {
return description;
}
}
1 | Declare the @Serdeable annotation at the type level in your source code to allow the type to be serialized or deserialized. |
2 | Use jakarta.validation.constraints Constraints to ensure the data matches your expectations. |
3 | Since the POJO does not have an empty constructor, use the annotations @BsonCreator and BsonProperty to define data conversion between BSON and POJO with the MongoDB Java driver. See POJOs without No-Argument Constructor. |
4 | Annotate with @Creator to provide a hint as to which constructor is the primary constructor. |
4.2. Repository
Create a repository interface to encapsulate the CRUD actions for Fruit
.
package example.micronaut;
import io.micronaut.core.annotation.NonNull;
import org.reactivestreams.Publisher;
import reactor.core.publisher.Mono;
import jakarta.validation.Valid;
import jakarta.validation.constraints.NotNull;
public interface FruitRepository {
@NonNull
Publisher<Fruit> list();
Mono<Boolean> save(@NonNull @NotNull @Valid Fruit fruit); (1)
}
1 | Add @Valid to any method parameter which requires validation. |
4.3. Controller
Create FruitController
:
package example.micronaut;
import io.micronaut.core.annotation.NonNull;
import io.micronaut.http.HttpStatus;
import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;
import io.micronaut.http.annotation.Post;
import org.reactivestreams.Publisher;
import reactor.core.publisher.Mono;
import jakarta.validation.Valid;
import jakarta.validation.constraints.NotNull;
import static io.micronaut.http.HttpStatus.CONFLICT;
import static io.micronaut.http.HttpStatus.CREATED;
@Controller("/fruits") (1)
class FruitController {
private final FruitRepository fruitService;
FruitController(FruitRepository fruitService) { (2)
this.fruitService = fruitService;
}
@Get (3)
Publisher<Fruit> list() {
return fruitService.list();
}
@Post (4)
Mono<HttpStatus> save(@NonNull @NotNull @Valid Fruit fruit) { (5)
return fruitService.save(fruit) (6)
.map(added -> added ? CREATED : CONFLICT);
}
}
1 | The class is defined as a controller with the @Controller annotation mapped to the path /fruits . |
2 | Use constructor injection to inject a bean of type FruitRepository . |
3 | The @Get annotation maps the list method to an HTTP GET request on /fruits . |
4 | The @Post annotation maps the save method to an HTTP POST request on /fruits . |
5 | Add @Valid to any method parameter which requires validation. |
6 | Micronaut controller methods can return reactive types |
4.4. Configuration
Create a configuration object to encapsulate the MongoDB database name and collection name.
package example.micronaut;
import io.micronaut.context.annotation.ConfigurationProperties;
import io.micronaut.core.annotation.NonNull;
import io.micronaut.core.naming.Named;
@ConfigurationProperties("db") (1)
public interface MongoDbConfiguration extends Named {
@NonNull
String getCollection();
}
1 | The @ConfigurationProperties annotation takes the configuration prefix. |
Define the values via configuration:
db:
name: 'fruit'
collection: 'fruit'
4.5. MongoDB repository
Implement FruitRepository
by using a MongoClient
package example.micronaut;
import com.mongodb.reactivestreams.client.MongoClient;
import com.mongodb.reactivestreams.client.MongoCollection;
import io.micronaut.core.annotation.NonNull;
import jakarta.inject.Singleton;
import org.reactivestreams.Publisher;
import reactor.core.publisher.Mono;
import jakarta.validation.Valid;
import jakarta.validation.constraints.NotNull;
@Singleton (1)
public class MongoDbFruitRepository implements FruitRepository {
private final MongoDbConfiguration mongoConf;
private final MongoClient mongoClient;
public MongoDbFruitRepository(MongoDbConfiguration mongoConf, (2)
MongoClient mongoClient) { (3)
this.mongoConf = mongoConf;
this.mongoClient = mongoClient;
}
@Override
public Mono<Boolean> save(@NonNull @NotNull @Valid Fruit fruit) {
return Mono.from(getCollection().insertOne(fruit)) (4)
.map(insertOneResult -> true)
.onErrorReturn(false);
}
@Override
@NonNull
public Publisher<Fruit> list() {
return getCollection().find(); (4)
}
@NonNull
private MongoCollection<Fruit> getCollection() {
return mongoClient.getDatabase(mongoConf.getName())
.getCollection(mongoConf.getCollection(), Fruit.class);
}
}
1 | Use jakarta.inject.Singleton to designate a class as a singleton. |
2 | Use constructor injection to inject a bean of type MongoDbConfiguration . |
3 | Use constructor injection to inject a bean of type MongoClient . |
4 | MongoClient methods return reactive sequences. |
By using the feature mongo-reactive
, the application includes the following dependency:
<dependency>
<groupId>io.micronaut.mongodb</groupId>
<artifactId>micronaut-mongo-reactive</artifactId>
<scope>compile</scope>
</dependency>
This registers a non-blocking reactive streams MongoDB client with MongoClient, which you can inject in other Micronaut beans as illustrated in the above code sample.
4.6. Test
Add a Micronaut declarative HTTP Client to src/test
to ease the testing of the application’s API.
package example.micronaut;
import io.micronaut.core.annotation.NonNull;
import io.micronaut.http.HttpStatus;
import io.micronaut.http.annotation.Get;
import io.micronaut.http.annotation.Post;
import io.micronaut.http.client.annotation.Client;
import jakarta.validation.Valid;
import jakarta.validation.constraints.NotNull;
import java.util.List;
@Client("/fruits")
public interface FruitClient {
@Post
@NonNull
HttpStatus save(@NonNull @NotNull @Valid Fruit fruit);
@NonNull
@Get
List<Fruit> findAll();
}
By using the feature mongo-sync
, the application includes the following test dependencies:
<dependency>
<groupId>org.testcontainers</groupId>
<artifactId>junit-jupiter</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.testcontainers</groupId>
<artifactId>mongodb</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.testcontainers</groupId>
<artifactId>testcontainers</artifactId>
<scope>test</scope>
</dependency>
Test Resources will provide us with a MongoDB instance for local testing and execution.
Create a test:
package example.micronaut;
import io.micronaut.http.HttpStatus;
import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
import jakarta.inject.Inject;
import org.junit.jupiter.api.AfterAll;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.Timeout;
import org.junit.jupiter.api.TestInstance;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import static io.micronaut.http.HttpStatus.CREATED;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertNull;
import static org.junit.jupiter.api.Assertions.assertTrue;
import static org.junit.jupiter.api.TestInstance.Lifecycle.PER_CLASS;
@MicronautTest
@TestInstance(PER_CLASS)
public class FruitControllerTest {
@Inject
FruitClient fruitClient;
@Test
@Timeout(120)
void fruitsEndpointInteractsWithMongo() {
List<Fruit> fruits = fruitClient.findAll();
assertTrue(fruits.isEmpty());
HttpStatus status = fruitClient.save(new Fruit("banana"));
assertEquals(CREATED, status);
fruits = fruitClient.findAll();
assertFalse(fruits.isEmpty());
assertEquals("banana", fruits.get(0).getName());
assertNull(fruits.get(0).getDescription());
status = fruitClient.save(new Fruit("Apple", "Keeps the doctor away"));
assertEquals(CREATED, status);
fruits = fruitClient.findAll();
assertTrue(fruits.stream().anyMatch(f -> "Keeps the doctor away".equals(f.getDescription())));
}
}
5. Test Resources
When the application is started locally — either under test or by running the application — resolution of the property mongodb.uri
is detected and the Test Resources service will start a local MongoDB docker container, and inject the properties required to use this as the datasource.
When running under production, you should replace this property with the location of your production MongoDB instance via an environment variable.
MONGODB_URI=mongodb://username:password@production-server:27017/databaseName
For more information, see the MongoDB section of the Test Resources documentation.
6. Testing the Application
To run the tests:
./mvnw test
7. Running the Application
To run the application, use the ./mvnw mn:run
command, which starts the application on port 8080.
curl -d '{"name":"Pear"}'
-H "Content-Type: application/json"
-X POST http://localhost:8080/fruits
curl -i localhost:8080/fruits
HTTP/1.1 200 OK
date: Wed, 15 Sep 2021 12:40:15 GMT
Content-Type: application/json
content-length: 110
connection: keep-alive
[{"name":"Pear"}]
8. Generate a Micronaut Application Native Executable with GraalVM
We will use GraalVM, the polyglot embeddable virtual machine, to generate a native executable of our Micronaut application.
Compiling native executables ahead of time with GraalVM improves startup time and reduces the memory footprint of JVM-based applications.
Only Java and Kotlin projects support using GraalVM’s native-image tool. Groovy relies heavily on reflection, which is only partially supported by GraalVM.
|
8.1. GraalVM installation
sdk install java 17.0.8-graal
sdk use java 17.0.8-graal
For installation on Windows, or for manual installation on Linux or Mac, see the GraalVM Getting Started documentation.
The previous command installs Oracle GraalVM, which is free to use in production and free to redistribute, at no cost, under the GraalVM Free Terms and Conditions.
Alternatively, you can use the GraalVM Community Edition:
sdk install java 17.0.8-graalce
sdk use java 17.0.8-graalce
8.2. Native executable generation
To generate a native executable using Maven, run:
./mvnw package -Dpackaging=native-image
The native executable is created in the target
directory and can be run with target/micronautguide
.
Consume the endpoints exposed by the native executable with cURL:
curl -d '{"name":"Pear"}'
-H "Content-Type: application/json"
-X POST http://localhost:8080/fruits
curl -i localhost:8080/fruits
HTTP/1.1 200 OK
date: Wed, 15 Sep 2021 12:40:15 GMT
Content-Type: application/json
content-length: 110
connection: keep-alive
[{"name":"Pear"}]
9. Next steps
Explore more features with Micronaut Guides.
10. Next Steps
Read more about the integration between the Micronaut framework and MongoDB.
11. Help with the Micronaut Framework
The Micronaut Foundation sponsored the creation of this Guide. A variety of consulting and support services are available.
12. License
All guides are released with an Apache license 2.0 license for the code and a Creative Commons Attribution 4.0 license for the writing and media (images…). |