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1. Micronaut Grails

1.1. Grails 4

1.1.1. Installation

Gradle
compile 'com.agorapulse:micronaut-grails:3.3.0-micronaut-3.0'

// for Tomcat deployment replace
// compile 'org.grails:grails-web-boot'
// with
compile 'com.agorapulse:micronaut-grails-web-boot:3.3.0-micronaut-3.0'
If you plan to reuse same library for Micronaut and Grails, you can declare the dependency as compileOnly.

1.1.2. Usage

Micronaut Grails library helps to use Micronaut beans in the Grails 4 application or any other Spring application. The main additional feature is the ability to do more customisation to the Micronaut context such as adding a package for scanning.

Replace the body of the main method inside grails-app/init/…​/Application.groovy with the following code.

Grails 4 Usage
import com.agorapulse.micronaut.grails.CompatibilityMode
import com.agorapulse.micronaut.grails.EnvVarLikeSystemPropertiesPropertySource
import com.agorapulse.micronaut.grails.MicronautGrailsApp
import com.agorapulse.micronaut.grails.MicronautGrailsAutoConfiguration
import com.agorapulse.micronaut.grails.domain.Manager
import groovy.transform.CompileStatic
import io.micronaut.context.env.Environment
import org.springframework.context.ConfigurableApplicationContext

@CompileStatic
class Application extends MicronautGrailsAutoConfiguration {                            (1)

    static ConfigurableApplicationContext context

    static void main(String[] args) {
        context = MicronautGrailsApp.run(Application, args)                             (2)
    }

    final CompatibilityMode compatibilityMode = CompatibilityMode.STRICT                (3)
    final Collection<Package> packages = [                                              (4)
        Manager.package,
    ]

    @Override
    protected void doWithMicronautEnvironment(Environment env) {
        env.addPropertySource(new EnvVarLikeSystemPropertiesPropertySource())           (5)
    }

}
1 Your Application class must extend MicronautGrailsAutoConfiguration class
2 Use MicronautGrailsApp instead of GrailsApp
3 You can set the compatibility mode (see below - defaults to STRICT)
4 You can customize the packages for scanning
5 You can customize the Micronaut environment
Compatibility Modes

The compatibility mode signals what is the level of compatibility with the legacy features mentioned in Grails 3 section. The default is STRICT which means no features are enabled and Grails 4 Micronaut out-of-box integration is used. If you are migrating from Grails 3 then you should select LEGACY and enable com.agorapulse.micronaut.grails logging to INFO to see the deprecation details.

Mode LEGACY BRIDGE STRICT

Single Application Context

No

Yes

Yes

If No then two application contexts are created - one for beans using @Inject and another one for beans injected by name.

Injection by Name

Yes

Yes

No

If No then the beans require @Inject annotation at the injection point, and they can be no longer injected by name.

Property Translation

Yes

No

No

If No then Spring beans of type PropertyTranslatingcustomiser are ignored prefix replacements no longer work. Otherwise, the customization applies to all beans injected by name (not using @Inject).

1.2. Grails 3

1.2.1. Installation

Gradle
compileOnly 'com.agorapulse:micronaut-grails:3.3.0-micronaut-3.0'
If you plan to reuse same library for Micronaut and Grails, you can declare the dependency as compileOnly.

1.2.2. Usage

Micronaut Grails library helps to use Micronaut beans in the Grails 3 application or any other Spring application. There are three additional features which cannot be found the official Spring support for Micronaut:

  1. Ability to modify Micronaut environment (e.g. add packages for scanning)

  2. Micronaut beans' names defaults to lower-cased simple name of the class as expected by Grails

  3. Ability to reuse existing properties declared by Grails - e.g. grails.redis.port can be injected as @Value('${redis.port}')

The integration is handled by bean processor which needs to be injected into Spring application context. The easiest thing is to create Spring configuration placed next to your Micronaut classes. The Spring configuration class will create MicronautBeanImporter which will be later processed by the processor bean:

@CompileStatic
@Configuration                                                                          (1)
class GrailsConfig {

    @Bean
    MicronautBeanImporter myImporter() {                                                (2)
        return MicronautBeanImporter.create()
            .addByType(Widget)                                                          (3)
            .addByType('someInterface', SomeInterface)                                  (4)
            .addByStereotype('custom', SomeCustomScope)                                 (5)
            .addByName('gadget')                                                        (6)
            .addByName('one')
            .addByName('two')
            .addByQualifiers(                                                           (7)
                'otherMinion',
                Qualifiers.byName('other'),
                Qualifiers.byType(Minion)
            )
    }

}
1 Define class as Spring @Configuration
2 Declare method which returns bean processor @Bean
3 The name of the Spring bean defaults to the property name of the class, e.g. widget
4 You can provide a different name
5 You can qualify using a stereotype (annotation)
6 You can qualify using the name of the bean which will be the same in the Spring application
7 You can combine any qualifiers possible to narrow the search to single bean which needs to be available from the Spring application context
If more than one bean qualifies the criteria then an exception will be thrown.

Once you have your configuration class ready then you can create META-INF/spring.factories descriptor in resources folder which will automatically load the configuration once the JAR is on classpath.

META-INF/spring.factories
org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.agorapulse.micronaut.grails.example.GrailsConfig

1.3. Integration Tests

If you want to take advantage of additional features provided by MicronautGrailsApp such additional package scanning inside integration tests then you need to use a following extension of the standard testing library:

Gradle
compile 'com.agorapulse:micronaut-grails-integration-test:3.3.0-micronaut-3.0'

Once the library is on the classpath, use @MicronautGrailsIntegration instead of @Inegration annotation to achieve the similar result:

import com.agorapulse.micronaut.grails.jpa.generator.MicronautJpaGenerator
import com.agorapulse.micronaut.grails.test.MicronautGrailsIntegration
import org.springframework.beans.factory.annotation.Autowired
import spock.lang.Specification

@MicronautGrailsIntegration
class IntegrationSpec extends Specification {

    @Autowired MicronautJpaGenerator generator

    void 'application started'() {
        expect:
            new URL("http://localhost:$serverPort/test/health").text == 'OK'
    }

}

1.4. GORM to Micronaut Data JPA Generator

1.4.1. Installation

Gradle
testImplementation 'com.agorapulse:micronaut-grails-jpa-generator:3.3.0-micronaut-3.0'

1.4.2. Usage

There is an experimental generator for the JPA entities from GORM domain classes. You can use either from integration test or using Grails Console plugin

You can use MicronautJdbcGenrator instead of MicronautJpaGenerator to generate JDBC repositories instead of generic ones.
Grails Integration Test Usage
import com.agorapulse.micronaut.grails.jpa.generator.MicronautJpaGenerator
import com.agorapulse.micronaut.grails.test.MicronautGrailsIntegration
import com.agorapulse.testing.fixt.Fixt
import org.springframework.beans.factory.annotation.Autowired
import spock.lang.Specification

@MicronautGrailsIntegration
class GeneratorSpec extends Specification {

    Fixt fixt = Fixt.create(GeneratorSpec)

    @Autowired MicronautJpaGenerator generator

    void 'generate domains'() {
        given:
            File root = initRootDirectory()
        when:
            generator.generate(root)
        then:
            noExceptionThrown()

        when:
            File entityFile = new File(root, 'micronaut/grails/example/model/User.groovy')
            File repositoryFile = new File(root, 'micronaut/grails/example/model/UserRepository.groovy')
        then:
            entityFile.exists()
            entityFile.text.trim() == fixt.readText('User.groovy.txt').trim()

            repositoryFile.exists()
            repositoryFile.text.trim() == fixt.readText('UserRepository.groovy.txt').trim()
    }

    private static File initRootDirectory() {
        File root = new File(System.getProperty('java.io.tmpdir'), 'micronaut-data-model')

        if (root.exists()) {
            root.deleteDir()
        }

        root.mkdirs()

        return root
    }

}
Micronaut Test Usage
import com.agorapulse.micronaut.grails.jpa.generator.MicronautJpaGenerator
import com.agorapulse.testing.fixt.Fixt
import groovy.transform.CompileDynamic
import io.micronaut.context.ApplicationContext
import org.grails.datastore.gorm.validation.constraints.eval.DefaultConstraintEvaluator
import org.grails.orm.hibernate.HibernateDatastore
import spock.lang.AutoCleanup
import spock.lang.Specification

/**
 * Example specification generating JPA entities from GORM entities.
 */
@CompileDynamic
class MicronautGeneratorSpec extends Specification {

    Fixt fixt = Fixt.create(MicronautGeneratorSpec)

    @AutoCleanup ApplicationContext context = ApplicationContext.run()

    MicronautJpaGenerator generator = new MicronautJpaGenerator(
        context.getBean(HibernateDatastore),
        new DefaultConstraintEvaluator()
    )

    void 'generate domains'() {
        given:
            File root = initRootDirectory()
        when:
            generator.generate(root)
        then:
            noExceptionThrown()

        when:
            File entityFile = new File(root, 'com/agorapulse/micronaut/grails/domain/model/Manager.groovy')
            File repositoryFile = new File(root, 'com/agorapulse/micronaut/grails/domain/model/ManagerRepository.groovy')
        then:
            entityFile.exists()
            entityFile.text.trim() == fixt.readText('Manager.groovy.txt').trim()

            repositoryFile.exists()
            repositoryFile.text.trim() == fixt.readText('ManagerRepository.groovy.txt').trim()
    }

    private static File initRootDirectory() {
        File root = new File(System.getProperty('java.io.tmpdir'), 'micronaut-data-model')

        if (root.exists()) {
            root.deleteDir()
        }

        root.mkdirs()

        return root
    }

}
Grails Console Usage
ctx.micronautJpaGenerator.generate(new File('/path/to/generated/sources'))
Micronaut Console Usage
import com.agorapulse.micronaut.grails.jpa.generator.MicronautJpaGenerator
import org.grails.datastore.gorm.validation.constraints.eval.DefaultConstraintEvaluator
import org.grails.orm.hibernate.HibernateDatastore

new MicronautJpaGenerator(
    ctx.getBean(HibernateDatastore),
    new DefaultConstraintEvaluator()
).generate(new File('/path/to/generated/sources'))

The current generator supports

  • Constraints

  • Column mappings

  • One-to-One, One-to-Many and Many-to-One relationships

  • Join Tables

  • Unique and regular indices

Please, let us know if there is any feature missing!

The new entities are generated it to the packages with suffix .model.

1.4.3. Generated Entities Example

For an User entity such as this one

GORM Entity
package micronaut.grails.example

import grails.compiler.GrailsCompileStatic
import micronaut.grails.example.other.Vehicle

@GrailsCompileStatic
class User {

    String userName
    String password
    String email

    static hasMany = [vehicles: Vehicle]

    static constraints = {
        userName blank: false, unique: true
        password size: 5..10, blank: false
        email email: true, blank: true
    }

}

The following files are generated

Micronaut Data JPA Entity
package micronaut.grails.example.model

import groovy.transform.CompileStatic
import javax.persistence.Entity
import javax.persistence.GeneratedValue
import javax.persistence.GenerationType
import javax.persistence.Id
import javax.persistence.OneToMany
import javax.persistence.Table
import javax.persistence.UniqueConstraint
import javax.persistence.Version
import javax.validation.constraints.Email
import javax.validation.constraints.NotBlank
import javax.validation.constraints.NotNull
import javax.validation.constraints.Size
import micronaut.grails.example.other.model.Vehicle

@Entity
@CompileStatic
@Table(
    uniqueConstraints = [
        @UniqueConstraint(columnNames = ['user_name'])
    ]
)
class User {

    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    Long id

    @Version
    Long version

    @NotNull
    @Email
    @Size(max = 255)
    String email

    @NotNull
    @Size(min = 5, max = 10)
    @NotBlank
    @Size(min = 5, max = 10)
    String password

    @NotNull
    @NotBlank
    @Size(max = 255)
    String userName

    @OneToMany
    Set<Vehicle> vehicles

}
Micronaut Data Repository
package micronaut.grails.example.model

import io.micronaut.data.annotation.Repository
import io.micronaut.data.repository.CrudRepository

@Repository
interface UserRepository extends CrudRepository<User, Long> {

}

1.5. Troubleshooting

1.5.1. Dumping Configuration Properties

The configuration properties inside Grails may behave bit differently than inside Micronaut application. If you are using Grails Console plugin then you can dump all the properties available using the following script

def mc = ctx.getBean(com.agorapulse.micronaut.grails.MicronautContextHolder).context
def env = mc.environment
def sources = env.propertySources


for (source in sources) {
    println "$source.name:"
    for (name in source) {
        def value = source.get(name)
        println "  $name (${value?.getClass()}): ${String.valueOf(value)}"
    }
}

2. Links

Javadoc

Source