Add Kotlin example with all-open setting

[vladmihalcea]

When using Kotlin, you need to add the following all-open dependency:

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

And add the following configuration to the kotlin-maven-plugin:

<plugin>
    <artifactId>kotlin-maven-plugin</artifactId>
    <groupId>org.jetbrains.kotlin</groupId>
    <version>${kotlin.version}</version>
    <configuration>
        <compilerPlugins>
            ...
            <plugin>all-open</plugin>
        </compilerPlugins>
        <pluginOptions>
            <option>all-open:annotation=javax.persistence.Entity</option>
            <option>all-open:annotation=javax.persistence.MappedSuperclass</option>
            <option>all-open:annotation=javax.persistence.Embeddable</option>
        </pluginOptions>
    </configuration>
    <executions>
        <execution>
            <id>compile</id>
            <goals>
                <goal>compile</goal>
            </goals>
            <configuration>
                <sourceDirs>
                    <sourceDir>${project.basedir}/src/main/kotlin</sourceDir>
                    <sourceDir>${project.basedir}/src/main/java</sourceDir>
                </sourceDirs>
            </configuration>
        </execution>
        <execution>
            <id>test-compile</id>
            <goals>
                <goal>test-compile</goal>
            </goals>
            <configuration>
                <sourceDirs>
                    <sourceDir>${project.basedir}/src/test/kotlin</sourceDir>
                    <sourceDir>${project.basedir}/src/test/java</sourceDir>
                </sourceDirs>
            </configuration>
        </execution>
    </executions>
</plugin>

For more details, check out this article.

[vladmihalcea]

Fixed.