Access a database with JPA and Hibernate Reactive

Learn how to use Hibernate Reactive with the Micronaut Framework.

Authors: Tim Yates, Roman Naglic

Micronaut Version: 4.3.8

1. Getting Started

In this guide, we will create a Micronaut application written in Java.

In this guide, we will write a Micronaut application that exposes some REST endpoints and stores data in a database using JPA and Hibernate.

2. What you will need

To complete this guide, you will need the following:

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.

4. Writing the Application

Create an application using the Micronaut Command Line Interface or with Micronaut Launch.

mn create-app example.micronaut.micronautguide --build=maven --lang=java
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.

4.1. Data Source configuration

Add the following dependencies:

pom.xml
<dependency> (1)
    <groupId>io.micronaut.reactor</groupId>
    <artifactId>micronaut-reactor</artifactId>
    <scope>compile</scope>
</dependency>
<dependency> (2)
    <groupId>io.micronaut.sql</groupId>
    <artifactId>micronaut-hibernate-reactive</artifactId>
    <scope>compile</scope>
</dependency>
<dependency> (3)
    <groupId>io.vertx</groupId>
    <artifactId>vertx-mysql-client</artifactId>
    <scope>compile</scope>
</dependency>
1 Add a dependency to the Micronaut Framework Project Reactor support
2 Configures Hibernate Reactive/JPA beans.
3 Adds a dependency to the Vert.x MySQL client.

4.2. JPA configuration

Add the next snippet to src/main/resources/application.yml to configure JPA:

src/main/resources/application.yml
jpa:
  default:
    reactive: true
    properties:
      hibernate:
        connection:
          db-type: mysql
        hbm2ddl:
          auto: create-drop
        show_sql: true

4.3. Domain

Create the domain entities:

src/main/java/example/micronaut/domain/Genre.java
package example.micronaut.domain;


import io.micronaut.serde.annotation.Serdeable;
import com.fasterxml.jackson.annotation.JsonIgnore;

import jakarta.persistence.Column;
import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.Id;
import jakarta.persistence.OneToMany;
import jakarta.persistence.Table;
import jakarta.validation.constraints.NotNull;
import java.util.HashSet;
import java.util.Set;

import static jakarta.persistence.GenerationType.AUTO;

@Serdeable
@Entity
@Table(name = "genre")
public class Genre {

    @Id
    @GeneratedValue(strategy = AUTO)
    private Long id;

    @NotNull
    @Column(name = "name", nullable = false, unique = true)
    private String name;

    @JsonIgnore
    @OneToMany(mappedBy = "genre")
    private Set<Book> books = new HashSet<>();

    public Genre() {}

    public Genre(@NotNull String name) {
        this.name = name;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Set<Book> getBooks() {
        return books;
    }

    public void setBooks(Set<Book> books) {
        this.books = books;
    }

    @Override
    public String toString() {
        return "Genre{" +
            "id=" + id +
            ", name='" + name + '\'' +
            '}';
    }
}

The previous domain has a OneToMany relationship with the domain Book.

src/main/java/example/micronaut/domain/Book.java
package example.micronaut.domain;

import io.micronaut.serde.annotation.Serdeable;

import jakarta.persistence.Column;
import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.Id;
import jakarta.persistence.ManyToOne;
import jakarta.persistence.Table;
import jakarta.validation.constraints.NotNull;

import static jakarta.persistence.GenerationType.AUTO;

@Serdeable
@Entity
@Table(name = "book")
public class Book {

    @Id
    @GeneratedValue(strategy = AUTO)
    private Long id;

    @NotNull
    @Column(name = "name", nullable = false)
    private String name;

    @NotNull
    @Column(name = "isbn", nullable = false)
    private String isbn;

    @ManyToOne
    private Genre genre;

    public Book() {}

    public Book(@NotNull String isbn,
                @NotNull String name,
                Genre genre) {
        this.isbn = isbn;
        this.name = name;
        this.genre = genre;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getIsbn() {
        return isbn;
    }

    public void setIsbn(String isbn) {
        this.isbn = isbn;
    }

    public Genre getGenre() {
        return genre;
    }

    public void setGenre(Genre genre) {
        this.genre = genre;
    }

    @Override
    public String toString() {
        return "Book{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", isbn='" + isbn + '\'' +
                ", genre=" + genre +
                '}';
    }
}

4.4. Application Configuration

Create an interface to encapsulate the application configuration settings:

src/main/java/example/micronaut/ApplicationConfiguration.java
package example.micronaut;

public interface ApplicationConfiguration {
    int getMax();
}

Like Spring Boot and Grails, in Micronaut applications you can create typesafe configuration by creating classes that are annotated with @ConfigurationProperties.

Create a ApplicationConfigurationProperties class:

src/main/java/example/micronaut/ApplicationConfigurationProperties.java
package example.micronaut;

import io.micronaut.context.annotation.ConfigurationProperties;

@ConfigurationProperties("application") (1)
public class ApplicationConfigurationProperties implements ApplicationConfiguration {

    private final int DEFAULT_MAX = 10;

    private int max = DEFAULT_MAX;

    @Override
    public int getMax() {
        return max;
    }

    public void setMax(int max) {
        this.max = max;
    }
}
1 The @ConfigurationProperties annotation takes the configuration prefix.

You can override max if you add to your src/main/resources/application.yml:

src/main/resources/application.yml
application:
  max: 50

4.5. Repository Access

Next, create a repository interface to define the operations to access the database:

src/main/java/example/micronaut/GenreRepository.java
package example.micronaut;

import example.micronaut.domain.Genre;
import io.micronaut.core.annotation.NonNull;
import org.reactivestreams.Publisher;

import jakarta.validation.constraints.NotBlank;
import java.util.Optional;

public interface GenreRepository {

    Publisher<Optional<Genre>> findById(long id);

    Publisher<Genre> save(@NotBlank String name);

    Publisher<Genre> saveWithException(@NotBlank String name);

    void deleteById(long id);

    Publisher<Genre> findAll(@NonNull SortingAndOrderArguments args);

    Publisher<Integer> update(long id, @NotBlank String name);
}

And the implementation:

src/main/java/example/micronaut/GenreRepositoryImpl.java
package example.micronaut;

import example.micronaut.domain.Genre;
import jakarta.inject.Singleton;
import org.hibernate.SessionFactory;
import org.hibernate.reactive.stage.Stage;
import org.reactivestreams.Publisher;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import jakarta.persistence.PersistenceException;
import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.concurrent.CompletionStage;

@Singleton (1)
public class GenreRepositoryImpl implements GenreRepository {

    private static final List<String> VALID_PROPERTY_NAMES = Arrays.asList("id", "name");
    private final ApplicationConfiguration applicationConfiguration;
    private final Stage.SessionFactory sessionFactory;

    public GenreRepositoryImpl(
            ApplicationConfiguration applicationConfiguration, (2)
            SessionFactory sessionFactory (3)
    ) {
        this.applicationConfiguration = applicationConfiguration;
        this.sessionFactory = sessionFactory.unwrap(Stage.SessionFactory.class);
    }

    @Override
    public Publisher<Optional<Genre>> findById(long id) {
        return Mono.fromCompletionStage(sessionFactory.withTransaction(session -> (4)
            find(session, id)
        ));
    }

    CompletionStage<Optional<Genre>> find(Stage.Session session, Long id) {
        return session.find(Genre.class, id).thenApply(Optional::ofNullable);
    }

    @Override
    public Publisher<Genre> save(String name) {
        return Mono.fromCompletionStage(sessionFactory.withTransaction(session -> {
            Genre entity = new Genre(name);
            return session.persist(entity).thenApply(v -> entity);
        }));
    }

    @Override
    public Publisher<Genre> saveWithException(String name) {
        return Mono.fromCompletionStage(sessionFactory.withTransaction(session -> {
            Genre entity = new Genre(name);
            return session.persist(entity).thenApply(v -> {
                throw new PersistenceException();
            });
        }));
    }

    @Override
    public void deleteById(long id) {
        sessionFactory.withTransaction(session -> session.find(Genre.class, id).thenApply(session::remove));
    }

    @Override
    public Publisher<Genre> findAll(SortingAndOrderArguments args) {
        String qlString = createQuery(args);
        return Mono.fromCompletionStage(sessionFactory.withTransaction(session -> {
                    Stage.SelectionQuery<Genre> query = session.createQuery(qlString, Genre.class);
                    query.setMaxResults(args.max() == null ? applicationConfiguration.getMax() : args.max());
                    if (args.offset() != null) {
                        query.setFirstResult(args.offset());
                    }
                    return query.getResultList();
                }))
                .flatMapMany(Flux::fromIterable);
    }

    private String createQuery(SortingAndOrderArguments args) {
        String qlString = "SELECT g FROM Genre as g";
        String order = args.order();
        String sort = args.sort();
        if (order != null && sort != null && VALID_PROPERTY_NAMES.contains(sort)) {
            qlString += " ORDER BY g." + sort + ' ' + order.toLowerCase();
        }
        return qlString;
    }

    @Override
    public Publisher<Integer> update(long id, String name) {
        return Mono.fromCompletionStage(sessionFactory.withTransaction(session -> session.createQuery("UPDATE Genre g SET name = :name where id = :id")
                        .setParameter("name", name)
                        .setParameter("id", id)
                        .executeUpdate()));
    }
}
1 Use jakarta.inject.Singleton to designate a class as a singleton.
2 Inject the ApplicationConfiguration.
3 Inject the Hibernate SessionFactory.
4 Grab a transactional session from the SessionFactory to run our query.

4.6. Controller

Micronaut validation is built on the standard framework – JSR 380, also known as Bean Validation 2.0. Micronaut Validation has built-in support for validation of beans that are annotated with jakarta.validation annotations.

To use Micronaut Validation, you need the following dependencies:

pom.xml
<!-- Add the following to your annotationProcessorPaths element -->
<path>
    <groupId>io.micronaut.validation</groupId>
    <artifactId>micronaut-validation-processor</artifactId>
</path>
<dependency>
    <groupId>io.micronaut.validation</groupId>
    <artifactId>micronaut-validation</artifactId>
    <scope>compile</scope>
</dependency>

Alternatively, you can use Micronaut Hibernate Validator, which uses Hibernate Validator; a reference implementation of the validation API.

Create two classes to encapsulate Save and Update operations:

src/main/java/example/micronaut/GenreSaveCommand.java
package example.micronaut;

import io.micronaut.serde.annotation.Serdeable;

import jakarta.validation.constraints.NotBlank;

@Serdeable (1)
public class GenreSaveCommand {

    @NotBlank
    private String name;

    public GenreSaveCommand(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}
1 Declare the @Serdeable annotation at the type level in your source code to allow the type to be serialized or deserialized.
src/main/java/example/micronaut/GenreUpdateCommand.java
package example.micronaut;

import io.micronaut.serde.annotation.Serdeable;

import jakarta.validation.constraints.NotBlank;

@Serdeable
public class GenreUpdateCommand {

    private long id;

    @NotBlank
    private String name;

    public GenreUpdateCommand(long id, String name) {
        this.id = id;
        this.name = name;
    }

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

Create a POJO to encapsulate Sorting and Pagination:

src/main/java/example/micronaut/SortingAndOrderArguments.java
package example.micronaut;

import io.micronaut.core.annotation.Nullable;
import io.micronaut.serde.annotation.Serdeable;
import jakarta.validation.constraints.Pattern;
import jakarta.validation.constraints.Positive;
import jakarta.validation.constraints.PositiveOrZero;

@Serdeable
public record SortingAndOrderArguments(
        @Nullable @PositiveOrZero Integer offset,
        @Nullable @Positive Integer max,
        @Nullable @Pattern(regexp = "id|name") String sort,
        @Nullable @Pattern(regexp = "asc|ASC|desc|DESC") String order
) {
}
1 Use jakarta.validation.constraints Constraints to ensure the incoming data matches your expectations.

Create GenreController, a controller which exposes a resource with the common CRUD operations:

src/main/java/example/micronaut/GenreController.java
package example.micronaut;

import example.micronaut.domain.Genre;
import io.micronaut.core.async.annotation.SingleResult;
import io.micronaut.http.HttpResponse;
import io.micronaut.http.HttpStatus;
import io.micronaut.http.MutableHttpResponse;
import io.micronaut.http.annotation.Body;
import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Delete;
import io.micronaut.http.annotation.Get;
import io.micronaut.http.annotation.Post;
import io.micronaut.http.annotation.Put;
import io.micronaut.http.annotation.Status;
import org.reactivestreams.Publisher;
import reactor.core.publisher.Mono;

import jakarta.persistence.PersistenceException;
import jakarta.validation.Valid;
import java.net.URI;

import static io.micronaut.http.HttpHeaders.LOCATION;

@Controller("/genres")  (1)
class GenreController {

    private final GenreRepository genreRepository;

    GenreController(GenreRepository genreRepository) { (2)
        this.genreRepository = genreRepository;
    }

    @Get("/{id}") (3)
    @SingleResult
    Publisher<Genre> show(Long id) {
        return Mono.from(genreRepository.findById(id))
                .flatMap(g -> g.map(Mono::just).orElseGet(Mono::empty)); (4)
    }

    @Put (5)
    Publisher<HttpResponse<?>> update(@Body @Valid GenreUpdateCommand command) { (6)
        return Mono.from(genreRepository.update(command.getId(), command.getName()))
                .map(i -> HttpResponse
                        .noContent()
                        .header(LOCATION, location(command.getId()).getPath())); (7)
    }

    @Get(value = "/list{?args*}") (8)
    Publisher<Genre> list(@Valid SortingAndOrderArguments args) {
        return genreRepository.findAll(args);
    }

    @Post (9)
    @SingleResult
    Publisher<HttpResponse<Genre>> save(@Body @Valid GenreSaveCommand cmd) {
        return Mono.from(genreRepository.save(cmd.getName()))
                .map(genre -> HttpResponse
                        .created(genre)
                        .headers(headers -> headers.location(location(genre.getId())))
                );
    }

    @Post("/ex") (10)
    @SingleResult
    Publisher<MutableHttpResponse<Genre>> saveExceptions(@Body @Valid GenreSaveCommand cmd) {
        return Mono.from(genreRepository.saveWithException(cmd.getName()))
                .map(genre -> HttpResponse
                        .created(genre)
                        .headers(headers -> headers.location(location(genre.getId()))))
                .onErrorReturn(PersistenceException.class, HttpResponse.noContent());
    }

    @Delete("/{id}") (11)
    @Status(HttpStatus.NO_CONTENT) (12)
    <T> HttpResponse<T> delete(Long id) {
        genreRepository.deleteById(id);
        return HttpResponse.noContent();
    }

    private URI location(Long id) {
        return URI.create("/genres/" + id);
    }
}
1 The class is defined as a controller with the @Controller annotation mapped to the path /genres.
2 Use constructor injection to inject a bean of type GenreRepository.
3 The @Get annotation maps the show method to an HTTP GET request on /{id}.
4 Returning an empty Publisher when the genre doesn’t exist makes the Micronaut framework respond with 404 (not found).
5 Maps a PUT request to /genres which attempts to update a genre.
6 Add @Valid to any method parameter which requires validation.
7 Add custom headers to the response.
8 Maps a GET request to /genres which returns a list of genres.
9 Maps a POST request to /genres which attempts to save a genre.
10 Maps a POST request to /ex which generates an exception.
11 The @Delete annotation maps the delete method to an HTTP Delete request on /genres/{id}.
12 You can return void in your controller’s method and specify the HTTP status code via the @Status annotation.

4.7. Writing Tests

Create a test to verify the CRUD operations:

src/test/java/example/micronaut/GenreControllerTest.java
package example.micronaut;

import example.micronaut.domain.Genre;
import io.micronaut.core.type.Argument;
import io.micronaut.http.HttpRequest;
import io.micronaut.http.HttpResponse;
import io.micronaut.http.client.BlockingHttpClient;
import io.micronaut.http.client.HttpClient;
import io.micronaut.http.client.annotation.Client;
import io.micronaut.http.client.exceptions.HttpClientResponseException;
import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.TestInstance;

import jakarta.inject.Inject;
import java.util.ArrayList;
import java.util.List;

import static io.micronaut.http.HttpHeaders.LOCATION;
import static io.micronaut.http.HttpStatus.BAD_REQUEST;
import static io.micronaut.http.HttpStatus.CREATED;
import static io.micronaut.http.HttpStatus.NOT_FOUND;
import static io.micronaut.http.HttpStatus.NO_CONTENT;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertNotNull;
import static org.junit.jupiter.api.Assertions.assertThrows;

@MicronautTest (1)
@TestInstance(TestInstance.Lifecycle.PER_CLASS) (2)
class GenreControllerTest {

    @Inject
    @Client("/")
    HttpClient httpClient; (3)

    private BlockingHttpClient blockingClient;

    @BeforeEach
    void setup() {
        blockingClient = httpClient.toBlocking();
    }

    @Test
    void supplyAnInvalidOrderTriggersValidationFailure() {
        HttpClientResponseException thrown = assertThrows(HttpClientResponseException.class, () ->
                blockingClient.exchange(HttpRequest.GET("/genres/list?order=foo"))
        );

        assertNotNull(thrown.getResponse());
        assertEquals(BAD_REQUEST, thrown.getStatus());
    }

    @Test
    void testFindNonExistingGenreReturns404() {
        HttpClientResponseException thrown = assertThrows(HttpClientResponseException.class, () ->
            blockingClient.exchange(HttpRequest.GET("/genres/99"))
        );

        assertNotNull(thrown.getResponse());
        assertEquals(NOT_FOUND, thrown.getStatus());
    }

    @Test
    void testGenreCrudOperations() {

        List<Long> genreIds = new ArrayList<>();

        HttpRequest<?> request = HttpRequest.POST("/genres", new GenreSaveCommand("DevOps")); (4)
        HttpResponse<?> response = blockingClient.exchange(request);
        genreIds.add(entityId(response));

        assertEquals(CREATED, response.getStatus());

        request = HttpRequest.POST("/genres", new GenreSaveCommand("Microservices")); (4)
        response = blockingClient.exchange(request);

        assertEquals(CREATED, response.getStatus());

        Long id = entityId(response);
        genreIds.add(id);
        request = HttpRequest.GET("/genres/" + id);

        Genre genre = blockingClient.retrieve(request, Genre.class); (5)

        assertEquals("Microservices", genre.getName());

        request = HttpRequest.PUT("/genres", new GenreUpdateCommand(id, "Micro-services"));
        response = blockingClient.exchange(request);  (6)

        assertEquals(NO_CONTENT, response.getStatus());

        request = HttpRequest.GET("/genres/" + id);
        genre = blockingClient.retrieve(request, Genre.class);
        assertEquals("Micro-services", genre.getName());

        request = HttpRequest.GET("/genres/list");
        List<Genre> genres = blockingClient.retrieve(request, Argument.of(List.class, Genre.class));

        assertEquals(2, genres.size());

        request = HttpRequest.POST("/genres/ex", new GenreSaveCommand("Microservices")); (4)
        response = blockingClient.exchange(request);

        assertEquals(NO_CONTENT, response.getStatus());

        request = HttpRequest.GET("/genres/list");
        genres = blockingClient.retrieve(request, Argument.of(List.class, Genre.class));

        assertEquals(2, genres.size());

        request = HttpRequest.GET("/genres/list?max=1");
        genres = blockingClient.retrieve(request, Argument.of(List.class, Genre.class));

        assertEquals(1, genres.size());
        assertEquals("DevOps", genres.get(0).getName());

        request = HttpRequest.GET("/genres/list?max=1&order=desc&sort=name");
        genres = blockingClient.retrieve(request, Argument.of(List.class, Genre.class));

        assertEquals(1, genres.size());
        assertEquals("Micro-services", genres.get(0).getName());

        request = HttpRequest.GET("/genres/list?max=1&offset=10");
        genres = blockingClient.retrieve(request, Argument.of(List.class, Genre.class));

        assertEquals(0, genres.size());

        // cleanup:
        for (Long genreId : genreIds) {
            request = HttpRequest.DELETE("/genres/" + genreId);
            response = blockingClient.exchange(request);
            assertEquals(NO_CONTENT, response.getStatus());
        }
    }

    private Long entityId(HttpResponse response) {
        String path = "/genres/";
        String value = response.header(LOCATION);
        if (value == null) {
            return null;
        }

        int index = value.indexOf(path);
        if (index != -1) {
            return Long.valueOf(value.substring(index + path.length()));
        }

        return null;
    }
}
1 Annotate the class with @MicronautTest so the Micronaut framework will initialize the application context and the embedded server. More info.
2 Classes that implement TestPropertyProvider must use this annotation to create a single class instance for all tests (not necessary in Spock tests).
3 Inject the HttpClient bean and point it to the embedded server.
4 Creating HTTP Requests is easy thanks to the Micronaut framework fluid API.
5 If you care just about the object in the response use retrieve.
6 Sometimes, receiving just the object is not enough and you need information about the response. In this case, instead of retrieve you should use the exchange method.

5. Testing the Application

To run the tests:

./mvnw test

6. Test Resources

When the application is started locally — either under test or by running the application — resolution of the datasource URL is detected and the Test Resources service will start a local MySQL docker container, and inject the properties required to use this as the datasource.

For more information, see the JDBC section or R2DBC section of the Test Resources documentation.

7. Using MySQL

When you move to production, you will need to configure the properties injected by Test Resources to point at your real production database. This can be done via environment variables like so:

export JPA_DEFAULT_PROPERTIES_HIBERNATE_CONNECTION_URL=jdbc:mysql://localhost:5432/micronaut
export JPA_DEFAULT_PROPERTIES_HIBERNATE_CONNECTION_USERNAME=dbuser
export JPA_DEFAULT_PROPERTIES_HIBERNATE_CONNECTION_PASSWORD=theSecretPassword

Run the application. If you look at the output you can see that the application uses MySQL:

8. Running the Application

To run the application, use the ./mvnw mn:run command, which starts the application on port 8080.

..
...
16:31:01.155 [main] INFO  org.hibernate.dialect.Dialect - HHH000400: Using dialect: org.hibernate.dialect.MySQL8Dialect
....

Connect to your MySQL database, and you will see both genre and book tables.

Save one genre, and your genre table will now contain an entry.

curl -X "POST" "http://localhost:8080/genres" \
     -H 'Content-Type: application/json; charset=utf-8' \
     -d $'{ "name": "music" }'

9. Next steps

Read more about Configurations for Data Access section in the Micronaut documentation.

10. Help with the Micronaut Framework

The Micronaut Foundation sponsored the creation of this Guide. A variety of consulting and support services are available.

11. 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…​).