Access a database with JPA and Hibernate

Learn how to access a database with JPA and Hibernate using the Micronaut framework.

Authors: Iván López, Sergio del Amo

Micronaut Version: 3.5.2

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:

  • Some time on your hands

  • A decent text editor or IDE

  • JDK 1.8 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.

4. Writing the Application

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

mn create-app example.micronaut.micronautguide --build=gradle --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.

The previous command creates a Micronaut application with the default package example.micronaut in a directory named micronautguide.

4.1. Enable annotation Processing

If you use Java or Kotlin and IntelliJ IDEA, make sure to enable annotation processing.

annotationprocessorsintellij

4.2. Data Source configuration

Add the following dependencies:

build.gradle
implementation("io.micronaut.sql:micronaut-hibernate-jpa") (1)
implementation("io.micronaut.sql:micronaut-jdbc-hikari") (2)
runtimeOnly("com.h2database:h2") (3)
implementation("jakarta.persistence:jakarta.persistence-api:2.2.3") (4)
1 Configures Hibernate/JPA EntityManagerFactory beans.
2 Configures SQL DataSource instances using Hikari Connection Pool.
3 Add dependency to in-memory H2 Database.
4 Add dependency to Jakarta Persistence API.

Define the data source in src/main/resources/application.yml.

src/main/resources/application.yml
datasources:
  default:
    url: ${JDBC_URL:`jdbc:h2:mem:default;DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=FALSE`}
    username: ${JDBC_USER:sa}
    password: ${JDBC_PASSWORD:""}
    driverClassName: ${JDBC_DRIVER:org.h2.Driver}
This way of defining the datasource properties means that we can externalize the configuration, for example for production environment, and also provide a default value for development. If the environment variables are not defined the Micronaut framework will use the default values.
Also keep in mind that it is necessary to escape the : in the connection URL using backticks `.

4.3. JPA configuration

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

src/main/resources/application.yml
jpa:
  default:
    properties:
      hibernate:
        hbm2ddl:
          auto: update
        show_sql: true

4.4. Domain

Create the domain entities:

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

import com.fasterxml.jackson.annotation.JsonIgnore;

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

import static javax.persistence.GenerationType.AUTO;

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

import static javax.persistence.GenerationType.AUTO;

@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 +
                '}';
    }
}

4.5. 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

4.6. Repository Access

To mark the transaction demarcations, we use the Java EE 7 javax.transaction.Transactional annotation.

To use it, you have to include the micronaut-data-processor dependency in your annotation processor configuration:

build.gradle
annotationProcessor("io.micronaut.data:micronaut-data-hibernate-jpa")

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 javax.validation.constraints.NotBlank;
import javax.validation.constraints.NotNull;
import java.util.List;
import java.util.Optional;

public interface GenreRepository {

    Optional<Genre> findById(long id);

    Genre save(@NotBlank String name);

    Genre saveWithException(@NotBlank String name);

    void deleteById(long id);

    List<Genre> findAll(@NotNull SortingAndOrderArguments args);

    int update(long id, @NotBlank String name);
}

The implementation:

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

import example.micronaut.domain.Genre;
import io.micronaut.transaction.annotation.ReadOnly;
import jakarta.inject.Singleton;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceException;
import javax.persistence.TypedQuery;
import javax.transaction.Transactional;
import javax.validation.constraints.NotBlank;
import javax.validation.constraints.NotNull;
import java.util.Arrays;
import java.util.List;
import java.util.Optional;

@Singleton (1)
public class GenreRepositoryImpl implements GenreRepository {

    private static final List<String> VALID_PROPERTY_NAMES = Arrays.asList("id", "name");

    private final EntityManager entityManager;  (2)
    private final ApplicationConfiguration applicationConfiguration;

    public GenreRepositoryImpl(EntityManager entityManager, (2)
                               ApplicationConfiguration applicationConfiguration) {
        this.entityManager = entityManager;
        this.applicationConfiguration = applicationConfiguration;
    }

    @Override
    @ReadOnly (3)
    public Optional<Genre> findById(long id) {
        return Optional.ofNullable(entityManager.find(Genre.class, id));
    }

    @Override
    @Transactional (4)
    public Genre save(@NotBlank String name) {
        Genre genre = new Genre(name);
        entityManager.persist(genre);
        return genre;
    }

    @Override
    @Transactional (4)
    public void deleteById(long id) {
        findById(id).ifPresent(entityManager::remove);
    }

    @ReadOnly (3)
    public List<Genre> findAll(@NotNull SortingAndOrderArguments args) {
        String qlString = "SELECT g FROM Genre as g";
        if (args.getOrder().isPresent() && args.getSort().isPresent() && VALID_PROPERTY_NAMES.contains(args.getSort().get())) {
            qlString += " ORDER BY g." + args.getSort().get() + ' ' + args.getOrder().get().toLowerCase();
        }
        TypedQuery<Genre> query = entityManager.createQuery(qlString, Genre.class);
        query.setMaxResults(args.getMax().orElseGet(applicationConfiguration::getMax));
        args.getOffset().ifPresent(query::setFirstResult);

        return query.getResultList();
    }

    @Override
    @Transactional (4)
    public int update(long id, @NotBlank String name) {
        return entityManager.createQuery("UPDATE Genre g SET name = :name where id = :id")
                .setParameter("name", name)
                .setParameter("id", id)
                .executeUpdate();
    }

    @Override
    @Transactional (4)
    public Genre saveWithException(@NotBlank String name) {
        save(name);
        throw new PersistenceException();
    }
}
1 Use jakarta.inject.Singleton to designate a class as a singleton.
2 Easily inject an EntityManager.
3 All database access needs to be wrapped inside a transaction. As the method only reads data from the database, annotate it with @ReadOnly.
4 This method modifies the database, thus it is annotated with @Transactional.

4.7. Controller

Micronaut validation is built on the standard framework – JSR 380, also known as Bean Validation 2.0.

Hibernate Validator is a reference implementation of the validation API. Micronaut has built-in support for validation of beans that are annotated with javax.validation annotations.

The necessary dependencies are included by default when creating a new application, so you don’t need to add anything else.

Create two classes to encapsulate Save and Update operations:

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

import io.micronaut.core.annotation.Introspected;

import javax.validation.constraints.NotBlank;

@Introspected (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 Annotate the class with @Introspected to generate BeanIntrospection metadata at compilation time. This information can be used, for example, to the render the POJO as JSON using Jackson without using reflection.
src/main/java/example/micronaut/GenreUpdateCommand.java
package example.micronaut;

import io.micronaut.core.annotation.Introspected;

import javax.validation.constraints.NotBlank;

@Introspected
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.Introspected;
import io.micronaut.core.annotation.Nullable;

import javax.validation.constraints.Pattern;
import javax.validation.constraints.Positive;
import javax.validation.constraints.PositiveOrZero;
import java.util.Optional;

@Introspected
public class SortingAndOrderArguments {

    @Nullable
    @PositiveOrZero (1)
    private Integer offset;

    @Nullable
    @Positive (1)
    private Integer max;

    @Nullable
    @Pattern(regexp = "id|name")  (1)
    private String sort;

    @Nullable
    @Pattern(regexp = "asc|ASC|desc|DESC")  (1)
    private String order;

    public Optional<Integer> getOffset() {
        return Optional.ofNullable(offset);
    }

    public void setOffset(@Nullable Integer offset) {
        this.offset = offset;
    }

    public Optional<Integer> getMax() {
        return Optional.ofNullable(max);
    }

    public void setMax(@Nullable Integer max) {
        this.max = max;
    }

    public Optional<String> getSort() {
        return Optional.ofNullable(sort);
    }

    public void setSort(@Nullable String sort) {
        this.sort = sort;
    }

    public Optional<String> getOrder() {
        return Optional.ofNullable(order);
    }

    public void setOrder(@Nullable String order) {
        this.order = order;
    }
}
1 Use javax.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.http.HttpResponse;
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.scheduling.TaskExecutors;
import io.micronaut.scheduling.annotation.ExecuteOn;

import javax.persistence.PersistenceException;
import javax.validation.Valid;
import java.net.URI;
import java.util.List;

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

@ExecuteOn(TaskExecutors.IO)  (1)
@Controller("/genres")  (2)
class GenreController {

    private final GenreRepository genreRepository;

    GenreController(GenreRepository genreRepository) { (3)
        this.genreRepository = genreRepository;
    }

    @Get("/{id}") (4)
    Genre show(Long id) {
        return genreRepository
                .findById(id)
                .orElse(null); (5)
    }

    @Put (6)
    HttpResponse<?> update(@Body @Valid GenreUpdateCommand command) { (7)
        int numberOfEntitiesUpdated = genreRepository.update(command.getId(), command.getName());

        return HttpResponse
                .noContent()
                .header(LOCATION, location(command.getId()).getPath()); (8)
    }

    @Get(value = "/list{?args*}") (9)
    List<Genre> list(@Valid SortingAndOrderArguments args) {
        return genreRepository.findAll(args);
    }

    @Post (10)
    HttpResponse<Genre> save(@Body @Valid GenreSaveCommand cmd) {
        Genre genre = genreRepository.save(cmd.getName());

        return HttpResponse
                .created(genre)
                .headers(headers -> headers.location(location(genre.getId())));
    }

    @Post("/ex") (11)
    HttpResponse<Genre> saveExceptions(@Body @Valid GenreSaveCommand cmd) {
        try {
            Genre genre = genreRepository.saveWithException(cmd.getName());
            return HttpResponse
                    .created(genre)
                    .headers(headers -> headers.location(location(genre.getId())));
        } catch(PersistenceException e) {
            return HttpResponse.noContent();
        }
    }

    @Delete("/{id}") (12)
    HttpResponse<?> delete(Long id) {
        genreRepository.deleteById(id);
        return HttpResponse.noContent();
    }

    private URI location(Long id) {
        return URI.create("/genres/" + id);
    }
}
1 It is critical that any blocking I/O operations (such as fetching the data from the database) are offloaded to a separate thread pool that does not block the Event loop.
2 The class is defined as a controller with the @Controller annotation mapped to the path /genres.
3 Constructor injection.
4 Maps a GET request to /genres/{id} which attempts to show a genre. This illustrates the use of a URL path variable.
5 Returning null when the genre doesn’t exist makes the Micronaut framework respond with 404 (not found).
6 Maps a PUT request to /genres which attempts to update a genre.
7 Add @Valid to any method parameter which requires validation. Use a POJO supplied as a JSON payload in the request to populate command.
8 It is easy to add custom headers to the response.
9 Maps a GET request to /genres which returns a list of genres. This mapping illustrates URL parameters being mapped to a single POJO.
10 Maps a POST request to /genres which attempts to save a genre.
11 Maps a POST request to /ex which generates an exception.
12 Maps a DELETE request to /genres/{id} which attempts to remove a genre. This illustrates the use of a URL path variable.

4.8. 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 jakarta.inject.Inject;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;

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)
class GenreControllerTest {

    private BlockingHttpClient blockingClient;

    @Inject
    @Client("/")
    HttpClient client; (2)

    @BeforeEach
    void setup() {
        blockingClient = client.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")); (3)
        HttpResponse<?> response = blockingClient.exchange(request);
        genreIds.add(entityId(response));

        assertEquals(CREATED, response.getStatus());

        request = HttpRequest.POST("/genres", new GenreSaveCommand("Microservices")); (3)
        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); (4)

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

        request = HttpRequest.PUT("/genres", new GenreUpdateCommand(id, "Micro-services"));
        response = blockingClient.exchange(request);  (5)

        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")); (3)
        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 Inject the HttpClient bean and point it to the embedded server.
3 Creating HTTP Requests is easy thanks to the Micronaut framework fluid API.
4 If you care just about the object in the response use retrieve.
5 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:

./gradlew test

Then open build/reports/tests/test/index.html in a browser to see the results.

6. Running the Application

To run the application, use the ./gradlew run command, which starts the application on port 8080.

7. Using PostgreSQL

When running on production you want to use a real database instead of using H2. Let’s explain how to use PostgreSQL.

After installing Docker, execute the following command to run a PostgreSQL container:

docker run -it --rm \
    -p 5432:5432 \
    -e POSTGRES_USER=dbuser \
    -e POSTGRES_PASSWORD=theSecretPassword \
    -e POSTGRES_DB=micronaut \
    postgres:11.5-alpine

Add PostgreSQL driver dependency:

build.gradle
runtimeOnly("org.postgresql:postgresql")

To use PostgreSQL, set up several environment variables which match those defined in application.yml:

export JDBC_URL=jdbc:postgresql://localhost:5432/micronaut
export JDBC_USER=dbuser
export JDBC_PASSWORD=theSecretPassword
export JDBC_DRIVER=org.postgresql.Driver

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

..
...
08:40:02.746 [main] INFO  org.hibernate.dialect.Dialect - HHH000400: Using dialect: org.hibernate.dialect.PostgreSQL10Dialect
....

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

datagrip

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" }'

8. Next steps

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

9. Help with the Micronaut Framework

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