Recently, I came across Micronaut, a super light framework that fills the need for something in between Spring Boot and Vert.x.

I have been playing with it and wanted to see if I could get a simple project with Micronaut, a Kotlin/Java intermix for the (main) source code, and Groovy/Spock tests. Turns out it's not that difficult. I just had to fiddle with it a little bit to get it right. So to save you time, here it is:

My requirements were:

• Source code in Kotlin and Java with circular dependency (just for fun)
• Test code exclusively in Groovy
• Maven based
• Micronaut as the base framework wiring everything together

mn create-app --features http-server --lang kotlin --build maven hello-world-example provided a great starting point. Then it was a matter of adding gmavenplus-plugin and maven-surefire-plugin.

Here's the source code. If you would like to know more about how the plugins work with each other, then read below. If not, feel free to dig around in the code.

1. To make Kotlin, Java, and Micronaut work together, you need kotlin-maven-plugin and maven-compiler-plugin as shown below.
2. Also, you need gmavenplus-plugin to compile groovy code.
3. Finally, you need maven-surefire-plugin to execute test(s).

pom.xml (kotlin-maven-plugin section responsible for kotlin, java and micronaut mix)

<plugin>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-maven-plugin</artifactId>
    <version>${kotlinVersion}</version>

    <configuration>
        <compilerPlugins>
            <plugin>all-open</plugin>
        </compilerPlugins>
        <pluginOptions>
            <option>all-open:annotation=io.micronaut.aop.Around</option>
        </pluginOptions>
    </configuration>

    <executions>
        <execution>                                                     (1)
            <id>kapt</id>
            <goals>
                <goal>kapt</goal>
            </goals>
            <configuration>
                <sourceDirs>
                    <sourceDir>src/main/kotlin</sourceDir>              (2)
                    <sourceDir>src/main/java</sourceDir>                (3)
                </sourceDirs>
                <annotationProcessorPaths>
                    <annotationProcessorPath>
                        <groupId>io.micronaut</groupId>
                        <artifactId>micronaut-inject-java</artifactId>
                        <version>${micronaut.version}</version>
                    </annotationProcessorPath>
                    <annotationProcessorPath>
                        <groupId>io.micronaut</groupId>
                        <artifactId>micronaut-validation</artifactId>
                        <version>${micronaut.version}</version>
                    </annotationProcessorPath>
                </annotationProcessorPaths>
            </configuration>
        </execution>

        <execution>                                                     (4)
            <id>compile</id>
            <goals>
                <goal>compile</goal>
            </goals>
            <configuration>
                <sourceDirs>
                    <sourceDir>src/main/kotlin</sourceDir>
                </sourceDirs>
            </configuration>
        </execution>

        <execution>                                                     (5)
            <id>test-kapt</id>
            <goals>
                <goal>test-kapt</goal>
            </goals>
            <configuration>
                <sourceDirs>
                    <sourceDir>src/test/kotlin</sourceDir>
                </sourceDirs>
                <annotationProcessorPaths>
                    <annotationProcessorPath>
                        <groupId>io.micronaut</groupId>
                        <artifactId>micronaut-inject-java</artifactId>
                        <version>${micronaut.version}</version>
                    </annotationProcessorPath>
                    <annotationProcessorPath>
                        <groupId>io.micronaut</groupId>
                        <artifactId>micronaut-validation</artifactId>
                        <version>${micronaut.version}</version>
                    </annotationProcessorPath>
                </annotationProcessorPaths>
            </configuration>
        </execution>

        <execution>
            <id>test-compile</id>
            <goals>
                <goal>test-compile</goal>
            </goals>
            <configuration>
                <sourceDirs>
                    <sourceDir>src/test/kotlin</sourceDir>
                    <sourceDir>target/generated-sources/kapt/test</sourceDir>
                </sourceDirs>
            </configuration>
        </execution>
    </executions>

    <dependencies>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-maven-allopen</artifactId>
            <version>${kotlinVersion}</version>
        </dependency>
    </dependencies>
</plugin>

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.7.0</version>
    <configuration>
        <proc>none</proc>
        <source>1.8</source>
        <target>1.8</target>
    </configuration>
    <executions>
        <execution>
            <id>default-compile</id>                                    (6)
            <phase>none</phase>
        </execution>
        <execution>
            <id>default-testCompile</id>                                (7)
            <phase>none</phase>
        </execution>
        <execution>
            <id>java-compile</id>
            <phase>compile</phase>
            <goals>
                <goal>compile</goal>
            </goals>
        </execution>
        <execution>
            <id>java-test-compile</id>
            <phase>test-compile</phase>
            <goals>
                <goal>testCompile</goal>
            </goals>
        </execution>
    </executions>
</plugin>

1. The Kapt compiler plugin provides support for annotation processors. micronaut does it's work at compile time. Hence, the kapt plugin is necessary.
2. Kotlin source location
3. Java source location
4. For compile goal provide kotlin source location
5. test-kapt is only necessary when writing tests in kotlin.

pom.xml (gmavenplus-plugin section responsible for groovy test code compilation)

            <plugin>
                <groupId>org.codehaus.gmavenplus</groupId>
                <artifactId>gmavenplus-plugin</artifactId>
                <version>1.6.1</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>addTestSources</goal>             (1)
                            <goal>compileTests</goal>               (2)
                        </goals>
                    </execution>
                </executions>
            </plugin>

1. Add test sources
2. Compile tests.

pom.xml (maven-surefire-plugin responsible for executing unit tests)

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-surefire-plugin</artifactId>
    <version>2.22.0</version>
    <configuration>
        <useFile>false</useFile>
        <includes>
            <include>**/*Spec.*</include>                       (1)
            <include>**/*Test.*</include>                       (2)
        </includes>
    </configuration>
</plugin>

1. Execute any class that ends with Spec or
2. Execute any class that ends with Test