Micronaut Gradle Plugin

A Gradle Plugin for Micronaut that configures the Micronaut BOM and sets up annotation processing.

This project consists of 2 plugins: one for applications and one for Micronaut libraries.

Quick Start

Template projects are available via Micronaut Launch for each language. To get started you can use the Micronaut CLI:

$ mn create-app demo --lang java
$ mn create-app demo --lang groovy
$ mn create-app demo --lang kotlin

Or if you don't have it installed via curl:

# for Java
$ curl https://launch.micronaut.io/demo.zip?lang=java -o demo.zip && unzip demo.zip -d demo && cd demo
# for Groovy
$ curl https://launch.micronaut.io/demo.zip?lang=groovy -o demo.zip && unzip demo.zip -d demo && cd demo
# for Kotlin
$ curl https://launch.micronaut.io/demo.zip?lang=kotlin -o demo.zip && unzip demo.zip -d demo && cd demo

Micronaut Library Plugin

plugins {
  id "io.micronaut.library" version "{version}"
}

The Micronaut library plugin applies the following modifications to the build:

Applies the Micronaut Bill of Materials (BOM)
Applies the java-library plugin
Configures annotation processing for the current language (Groovy, Java or Kotlin)

The micronaut DSL can be used to configure how this behaves.

The minimum requirement is to set the Micronaut version to use. This can be done by setting micronautVersion in gradle.properties or as follows in build.gradle:

micronaut {
    version "2.0.1"
}

Complete example with the default settings:

micronaut {
    version "2.0.1"
    processing {
        // Sets whether incremental annotation processing is enabled
        incremental true
        // Sets the module name.
        // This should be the same as the artifactId in the POM
        module project.name
        // Sets the group.
        // This should be th same as the groupId in the POM
        group project.group
        // Sets the Java package names containing any custom Micronaut 
        // meta annotations (new annotations annotated with say @Around). 
        // Generally used only for advanced cases such as defining new AOP
        // advice. If omitted however, incremental annotation processing
        // will not work correctly
        annotations "com.example.*"
        // additional sourceSets can be configured here to apply the BOM
        // and annotation processors to source sets other than 'main' 
        sourceSets(
             sourceSets.main        
        )     
    }   
}

Note that the Micronaut Library plugin can also be used with Groovy and Kotlin.

Kotlin Support

For Kotlin, the Kotlin jvm and kapt plugins must be configured:

plugins {
    id "org.jetbrains.kotlin.jvm" version "{kotlin.version}"
    id "org.jetbrains.kotlin.kapt" version "{kotlin.version}"
    id "io.micronaut.library" version "{version}"   
}

Minimal Build

With the io.micronaut.library plugin applied a minimal build to get started writing a library for Micronaut that written in Java and is tested with JUnit 5 looks like:

plugins {
    id 'io.micronaut.library' version '{version}'
}

version "0.1"
group "com.example"

repositories {
    mavenCentral()
}

micronaut {
    version = "2.0.1"
}

dependencies {
    testImplementation("io.micronaut.test:micronaut-test-junit5")
    testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine")
}

Micronaut Application Plugin

plugins {
  id "io.micronaut.application" version "{version}"
}

The Micronaut application plugin extends the Micronaut Library plugin and adds the following customizations:

Instead of the java-library plugin the plugin applies the Gradle application plugin.
If the current JVM is GraalVM configures a nativeImage task
Correctly configures Gradle for continuous build

The following additional tasks are provided by this plugin:

buildLayers - Builds application layers for use in a Docker container
dockerfile - Builds a Docker File for a Micronaut application
dockerBuild - Builds a Docker Image using the Docker Gradle plugin
dockerfileNative - Builds a Docker File for for GraalVM Native Image
dockerBuildNative - Builds a Native Docker Image using GraalVM Native Image
nativeImage - Builds a GraalVM Native Image
testNativeImage (since 1.1.0) - Builds a GraalVM Native Image, starts the native server and runs tests against the server
dockerPush - Pushes a Docker Image to configured container registry
dockerPushNative - Pushes a Docker Image built with GraalVM Native Image to configured container registry

To run an application with continuous build use the run task with the -t parameter:

$ ./gradlew run -t

Minimal Build

With the io.micronaut.application plugin applied a minimal build to get started with a Micronaut server application that is written in Java and tested with JUnit 5 looks like:

plugins {
    id 'io.micronaut.application' version '{version}'
}

version "0.1"
group "com.example"

repositories {
    mavenCentral()
}

micronaut {
    version = "2.0.1"
}

dependencies {
    implementation("io.micronaut:micronaut-http-server-netty")
    runtimeOnly("ch.qos.logback:logback-classic")
    testImplementation("io.micronaut.test:micronaut-test-junit5")
    testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine")
}

mainClassName = "example.Application"

Kotlin Support

The most simple Kotlin build using a build.gradle.kts file looks like:

plugins {
    id("org.jetbrains.kotlin.jvm") version "1.3.72"
    id("org.jetbrains.kotlin.kapt") version "1.3.72"
    id("org.jetbrains.kotlin.plugin.allopen") version "1.3.72"    
    id("io.micronaut.application") version "{version}"
}

version "0.1"
group "com.example"

repositories {
    mavenCentral()
}

micronaut {
    version( "2.0.1")
}

dependencies {
    implementation("io.micronaut:micronaut-http-server-netty")
    implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.3.72")
    implementation("org.jetbrains.kotlin:kotlin-reflect:1.3.72")
    runtimeOnly("ch.qos.logback:logback-classic")
    testImplementation("io.micronaut.test:micronaut-test-junit5")
    testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine")
}

application {
    mainClass.set("example.ApplicationKt")
}

GraalVM Native Image

If the JVM being used to build is a GraalVM SDK with the native-image tool enabled a nativeImage task is added that will build the native image using the currently active GraalVM distribution:

$./gradlew nativeImage

To configure Native Image arguments you can use the args method of the nativeImage task:

nativeImage {
    args('--static')
}

IMPORTANT: If you update an existing Micronaut application that contains the file src/main/resources/META-INF/native-image/xxxxx/native-image.properties, please make sure to delete the properties -H:Name and -H:Class from the file because they are managed automatically by the plugin.

Testing Native Images

Since 1.1.x of the plugin, you can also use the testNativeImage task to start the Micronaut native server and run tests against it.

IMPORTANT: This feature only works in combination with micronaut-test-core versions 2.2.1 or above. Make sure your test classpath includes at least this version of Micronaut Test.

Using this task will replace the regular embedded server used for tests with the natively built executable:

./gradlew testNativeImage

It is important to note that there are some limitations to this approach in that the native server is no longer "embedded" in the test. This has the following implications:

It is not possible to mock components using @MockBean or replace beans using @Replaces since the native server starts in a separate process and beans injected into or defined by the test are no longer shared with the application under test since it is running in a separate process.
The native server starts with the test environment active, however the classpath of the application is the runtime classpath not the test classpath. This has the implication that certain testing features (like for example Testcontainers' usage of JDBC URLs to start containers) won't work and you have to explicitly start any test containers in the test itself.

If you wish to split your native image tests from your regular tests you can create an additional source set for integration tests and the plugin will add an additional task suffixed with *NativeImage to run the native image tests, for example: gradle integrationTestNativeImage.

Docker Support

The Micronaut plugin includes integration with the Gradle Docker plugin allowing you to easily build applications and native images using Docker containers.

Applications are built as layered JARs using the buildLayers task ensuring optimized Docker images for Java applications.

To build a regular Java application into a Docker container that is ready to be deployed and exposes ports 8080 you can simply do:

$ ./gradlew dockerBuild

The default uses an OpenJDK 14 slim base image, however you can easily switch the base image to use by using the baseImage property of the dockerfile task:

dockerfile {
  baseImage = "oracle/graalvm-ce:20.3.0-java11"
}

The above examples switches to use GraalVM CE 20.3.0 as a base image.

To build the application into a Native Image you can run:

$ ./gradlew dockerBuildNative

Note that for this to work you must build the application with the same GraalVM SDK as used to build the image.

To push the container to the currently configure configured container registry you can use either dockerPush or dockerPushNative for the native image:

$ ./gradlew dockerPush

To configure the image names to push you can use the images setting of the dockerBuild task.

For example the following configures dockerPush to use Oracle Container Registry:

dockerBuild {
    images = ["eu-frankfurt-1.ocir.io/xyzzyz/repo/my-image:$project.version"]
}

dockerBuildNative {
    images = ["eu-frankfurt-1.ocir.io/xyzzyz/repo/my-image-native:$project.version"]
}

Notice that you can supply two different image names to push to for the JVM version and the native version of the application.

If you wish to customize the docker builds that are used, the easiest way is to run ./gradlew dockerfile (or dockerfileNative for the native version) and copy the generated Dockerfile from build/docker to your root directory and modify as required.

If you wish to customize the JVM arguments or native image arguments then it is possible to do so with the args method of the dockerfile and dockerfileNative tasks:

dockerfile {
 args("-Xmx128m")
}
dockerfileNative {
 args("-Xmx64m")
}

The above configuration uses a max heap setting of 128m for Java and 64m for native image for the application.

Micronaut Runtimes

A higher level concept of "runtimes" is included in the Micronaut Gradle plugin which essentially allows the plugin to decide which server runtime to include in the dependencies of the application when building the application. For example consider this minimal build:

plugins {
     id 'io.micronaut.application' version '{version}'
}
version "0.1"
group "com.example"

repositories {
    jcenter()
    mavenCentral()
}

micronaut {
    version = "2.0.1"
    runtime "netty"
}

dependencies {
    runtimeOnly("ch.qos.logback:logback-classic")
}

mainClassName = "example.Application"

Here the only dependency declared is on the logging framework to use however runtime is to netty resulting in an application that can be built and run.

If you wish to take the same and build or run it with a different runtime you can pass the micronaut.runtime property for the build. For example:

./gradlew run -Pmicronaut.runtime=google_function

The above example run the application as a Google Cloud Function.

The available runtimes are:

netty - A Netty server runtime
jetty - A Jetty server runtime
tomcat - A Tomcat server runtime
undertow - An Undertow server runtime
lambda - Allows building the application into an AWS Lambda
lambda_native - Allows building the applciation into a native AWS Lambda with GraalVM
oracle_function - A Project.fn runtime for deploying Oracle Functions
google_function - A runtime for deploying Google Functions.
azure_function - A runtime for deploying Azure Functions

The advantage of allowing your dependencies to be dictated by the runtime is that you can potentially take the same application and deploy it to any of the above runtimes without changes.

Packaging application

By default the plugin doesn't create a runnable fatjar when running ./gradlew assemble. There are a couple of options:

Layered application

The plugin creates a "layered" application in build/layers and from that directory you can run java -jar myapp.jar. It works because that directory contains a lib directory with all the libraries and a resources directory with the configuration. Keep in mind that copying the only .jar file to another directory won't work.

Add Shadow plugin

You can add Gradle Shadow plugin so when running ./gradlew assemble a runnable fatjar is created in build/libs directory.

plugins {
    ...
    id "com.github.johnrengelman.shadow" version "6.0.0"
    ...
}

ibmsoft/micronaut-gradle-plugin

Micronaut Gradle Plugin

Quick Start

Micronaut Library Plugin

Kotlin Support

Minimal Build

Micronaut Application Plugin

Minimal Build

Kotlin Support

GraalVM Native Image

Testing Native Images

Docker Support

Micronaut Runtimes

Packaging application

Layered application

Add Shadow plugin