Hibernate Metamodel annotation processor doesn't recognize Kotlin entity classes

Question

I have some entity classes in Java and some in Kotlin. I just added the following to my pom.xml:

    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-jpamodelgen</artifactId>
        <version>${hibernate.version}</version>
    </dependency>

IntelliJ now shows metamodel classes for the java entities, but not the kotlin ones. So I added kapt to no effect:

<plugin>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-maven-plugin</artifactId>
    <version>${kotlin.version}</version>
    <executions>
        <execution>
            <id>compile</id>
            <phase>compile</phase>
            <goals>
                <goal>compile</goal>
            </goals>
        </execution>
        <execution>
            <id>test-compile</id>
            <phase>test-compile</phase>
            <goals>
                <goal>test-compile</goal>
            </goals>
        </execution>
        <execution>
            <id>kapt</id>
            <goals>
                <goal>kapt</goal>
            </goals>
            <configuration>
                <sourceDirs>
                    <sourceDir>src/main/java</sourceDir>
                </sourceDirs>
                <annotationProcessorPaths>
                    <!-- Specify your annotation processors here. -->
                    <annotationProcessorPath>
                        <groupId>org.hibernate</groupId>
                        <artifactId>hibernate-jpamodelgen</artifactId>
                        <version>${hibernate.version}</version>
                    </annotationProcessorPath>
                </annotationProcessorPaths>
            </configuration>
        </execution>
    </executions>
    <configuration>
        <jvmTarget>11</jvmTarget>
        <args>
            <arg>-Xjvm-default=enable</arg>
            <!--<arg>-XXLanguage:+JvmStaticInInterface</arg>-->
        </args>
        <compilerPlugins>
            <plugin>jpa</plugin>
<!--                        <plugin>org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor</plugin>-->
        </compilerPlugins>
    </configuration>
    <dependencies>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-maven-noarg</artifactId>
            <version>${kotlin.version}</version>
        </dependency>
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-jpamodelgen</artifactId>
            <version>${hibernate.version}</version>
        </dependency>
    </dependencies>
</plugin>

I tried adding <plugin>org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor</plugin> to no apparent effect. I tried enabling annotation processing in IntelliJ IDEA:

Oh. I can see the generated files for the Kotlin classes in target/generated-sources/kapt/compile/ instead of target/generated-sources/annotations/. This may be as simple as setting the appropriate output directory.

Now when I run mvn clean compile I get errors just for the Java entity classes, saying that the annotations have already been run (presumably by kapt) and classes created:

[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ MyProject ---
[INFO] Deleting /myproject/target
[INFO] 
[INFO] --- kotlin-maven-plugin:1.3.70:kapt (kapt) @ MyProject ---
[WARNING] 'tools.jar' was not found, kapt may work unreliably
[INFO] Applied plugin: 'jpa'
[INFO] Note: Hibernate JPA 2 Static-Metamodel Generator 5.4.12.Final
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ MyProject ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 200 resources
[INFO] 
[INFO] --- kotlin-maven-plugin:1.3.70:compile (compile) @ MyProject ---
[INFO] Applied plugin: 'jpa'
[WARNING] Duplicate source root: /myproject/target/generated-sources/kapt/compile
[WARNING] Duplicate source root: /myproject/target/generated-sources/kaptKotlin/compile
[INFO] 
[INFO] --- maven-compiler-plugin:3.8.0:compile (java-compile) @ MyProject ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 261 source files to /myproject/target/classes
[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR : 
[INFO] -------------------------------------------------------------
[ERROR] Problem with Filer: Attempt to recreate a file for type my.project.db.SomeJavaClass_
[ERROR] Problem with Filer: Attempt to recreate a file for type my.project.db.AnotherJavaClass_
...

No. I don't know how to set the output directory. Nor do I know if that will actually solve it. — GlenPeterson
You don't have to set the output directory. This should be used by the compiler . Do you have problems compiling with Maven or only in Eclipse` — Simon Martinelli

GlenPeterson GlenPeterson · Accepted Answer · 2020-03-04T16:49:52

I deleted the project dependency on hibernate-jpamodelgen AND the Kotlin plugin dependency on the same, leaving it mentioned only in the annotationProcessorPath for kapt. Maven completed successfully.

<!-- Java has a fit if Kapt processes this first,
     so just let Kapt do it and don't tell Java about it. -->
<!--        <dependency>-->
<!--            <groupId>org.hibernate</groupId>-->
<!--            <artifactId>hibernate-jpamodelgen</artifactId>-->
<!--            <version>${hibernate.version}</version>-->
<!--        </dependency>-->

I also went back into the IntelliJ settings window, removed the JPAMetaModelEntityProcessor and unchecked "annotation processing." IntelliJ seems to be happy now too.

Hibernate Metamodel annotation processor doesn't recognize Kotlin entity classes

1 Answers