Zeebe exporter class cast exception

[Michal_Stefaniuk]

Hey guys, I’m working on a custom zeebe exporter. I had some issues with it before

Cannot register custom exporter

Hey guys, I was just playing around with zeebe exporters, I’m trying to register it in zeebe and somehow I’m getting this weirds error. Here is what I done: 1. Implemented a simple zeebe exporter Right now for testing purposes it’s very simple public class DemoExporter implements Exporter { Controller controller; public void open(Controller controller) { this.controller = controller; } public void export(Record record) { System.out.println(record.toJson()); …

Now my exporter has become a part of a multi module gradle project (I migrated it to maven) and unfortunately on zeebe startup I get this exception

java.lang.IllegalStateException: Failed to execute CommandLineRunner
        at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:774) [spring-boot-3.1.2.jar:3.1.2]
        at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:755) [spring-boot-3.1.2.jar:3.1.2]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:319) [spring-boot-3.1.2.jar:3.1.2]
        at io.camunda.zeebe.broker.StandaloneBroker.main(StandaloneBroker.java:82) [camunda-zeebe-8.3.0-alpha4.jar:8.3.0-alpha4]
Caused by: java.lang.IllegalStateException: Failed to load exporter with configuration: ExporterCfg{, jarPath='/usr/local/zeebe/lib/zeebe-exporter-demo-1.0-SNAPSHOT-jar-with-dependencies.jar', className='io.zeebe.exporters.Demo.DemoExporter', args={logLevel=debug, prettyPrint=false}}
        at io.camunda.zeebe.broker.Broker.buildExporterRepository(Broker.java:149) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.Broker.<init>(Broker.java:70) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.Broker.<init>(Broker.java:49) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.StandaloneBroker.run(StandaloneBroker.java:91) ~[camunda-zeebe-8.3.0-alpha4.jar:8.3.0-alpha4]
        at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:771) ~[spring-boot-3.1.2.jar:3.1.2]
        ... 3 more
Caused by: io.camunda.zeebe.broker.exporter.repo.ExporterLoadException: Cannot load exporter [demoexporter]: cannot load specified class
        at io.camunda.zeebe.broker.exporter.repo.ExporterRepository.load(ExporterRepository.java:82) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.Broker.buildExporterRepository(Broker.java:147) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.Broker.<init>(Broker.java:70) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.Broker.<init>(Broker.java:49) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.StandaloneBroker.run(StandaloneBroker.java:91) ~[camunda-zeebe-8.3.0-alpha4.jar:8.3.0-alpha4]
        at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:771) ~[spring-boot-3.1.2.jar:3.1.2]
        ... 3 more
Caused by: java.lang.ClassCastException: class io.zeebe.exporters.Demo.DemoExporter
        at java.lang.Class.asSubclass(Unknown Source) ~[?:?]
        at io.camunda.zeebe.broker.exporter.repo.ExporterRepository.load(ExporterRepository.java:80) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.Broker.buildExporterRepository(Broker.java:147) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.Broker.<init>(Broker.java:70) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.Broker.<init>(Broker.java:49) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.StandaloneBroker.run(StandaloneBroker.java:91) ~[camunda-zeebe-8.3.0-alpha4.jar:8.3.0-alpha4]
        at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:771) ~[spring-boot-3.1.2.jar:3.1.2]
        ... 3 more

Any thoughts on this one? I’m still building and deploying with java 11 so I hope it’s not a big deal (since Zeebe requires jdk+17). With maven and as a separate module it worked perfectly fine for me.

I was able to trace it in the zeebe codebase that there is a problem with exporter registartion and this is the line throwing exception:

try {
  final Class<?> specifiedClass = classLoader.loadClass(config.getClassName());
  --> exporterClass = specifiedClass.asSubclass(Exporter.class); <---
} catch (final ClassNotFoundException | ClassCastException e) {
  throw new ExporterLoadException(id, "cannot load specified class", e);
}

But I’m almost running out of ideas so any help is appreciated. Thanks.

[oleschoenburg]

Hey Michal

Just a guess as the stack trace really doesn’t give away much: Is your exporter compiled with the same version of Zeebe that you are trying to run it with?
I think if your dependency on Zeebe is for example 8.2.12 but you are deploying it to a Zeebe broker in version 8.2.13, you’d get a ClassCastException.

[adrianAzoitei]

@oleschoenburg

tack trace really doesn’t give away much: Is your exporter compiled with the same version of Zeebe that you are trying to run it with?

Did you manage to move past this? Running into the same now with Zeebe 8.5.0. Tried compiling the exporter to both jdk 17 and 21, with no success.