NiFi Custom Controller Service Implementation Setup

[#1]

I am trying to write an alternate implementation of the AtomicDistributedMapCacheClient<R> service. Specifically this is so that the "DistributedMapCacheLookupService" can use my implementation.

So far I have the class implementing the interface like so:

public class CustomDistributedMapCacheClientService extends AbstractControllerService implements AtomicDistributedMapCacheClient<Long> {
...
}

And I have a pom that generates the service-nar that looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>org.company</groupId>
    <artifactId>nifi.service.custom.nar</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>nar</packaging>


    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.javadoc.skip>true</maven.javadoc.skip>
        <source.skip>true</source.skip>
        <nifi.version>1.7.0</nifi.version>
    </properties>


    <dependencies>
	<!-- My Custom Java Code -->
        <dependency>
            <groupId>org.company</groupId>
            <artifactId>nifi.service.custom</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
	<!-- Add dependency to service api nar to make my implementation available on the classloaders. -->
        <dependency>
            <groupId>org.apache.nifi</groupId>
            <artifactId>nifi-standard-services-api-nar</artifactId>
            <version>${nifi.version}</version>
            <type>nar</type>
        </dependency>
    </dependencies>


    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.nifi</groupId>
                <artifactId>nifi-nar-maven-plugin</artifactId>
                <version>1.2.0</version>
                <extensions>true</extensions>
            </plugin>
        </plugins>
    </build>


    <repositories>
        <repository>
            <id>maven_central</id>
            <url>http://central.maven.org/maven2/</url>
        </repository>
    </repositories>
</project>

I set nifi-standard-services-api-nar as a dependency so that the classloaders will be configured properly. This lets me select my custom service in the DistributedMapCacheLookupService. However, it is showing this error in the UI:

... nifi.service.custom.nar is not compatible with DistributedMapCacheClient ...

I traced this message to this function: https://github.com/apache/nifi/blob/99bcd1f88dc826f857ae4ab33e842110bfc6ce21/nifi-nar-bundles/nifi-f... which returns false. Probably due to the classloading not being setup due to a problem with my pom.xml dependencies. Or I'm implementing the wrong class.

Is it possible to generate a custom service nar that adds an alternative implementation of the DistributedMapCacheClient service to be used by the DistributedMapCacheLookupService? Is there a template project I can refer to in order to set this up properly?

I have read through the Developer Guide on this a couple times: https://nifi.apache.org/docs/nifi-docs/html/developer-guide.html#nars but unfortunately am still confused as to how this works (an example project would help me a lot).

Thanks,

Alex

[#2]

Did you ever find a solution to this? I have the exact same problem.

[#3]

@chubbs As this thread is older, you would likely be better served by creating a new thread. This would also provide an opportunity to provide further details on your situation, steps taken so far and any errors encountered.