Getting ConcurrentModificationException with Kyro/Activiti and Spring Integration - spring-integration

Question

I am trying out to integrate Activiti with Spring Integration. The sample provided by Josh Long works but when i try to change it, specifically MessageChannels part, it starts throwing ConcurrentModificationException.
Josh Longs Activiti/Spring Integration example here.
As per Josh's code, MessageChannels is as follows:
#Configuration
class MessageChannels {
#Bean
DirectChannel requests() {
return new DirectChannel();
}
#Bean
DirectChannel replies() {
return new DirectChannel();
}
}
I changed this to spring integration (With Stream Rabbit) to
#Configuration
public interface MessageChannels {
#Input
SubscribableChannel input();
#Output("cooutput")
MessageChannel createOutput();
}
And my property file contains,
spring.cloud.stream.bindings.cooutput.destination=outputChannel
I am getting following exception, when i am calling "/start".
2016-09-10 16:14:39.087 INFO 73606 --- [ main] c.e.ActivitiIntegrationDemoApplication : Started ActivitiIntegrationDemoApplication in 8.236 seconds (JVM running for 8.759)
2016-09-10 16:15:39.524 INFO 73606 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring FrameworkServlet 'dispatcherServlet'
2016-09-10 16:15:39.524 INFO 73606 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : FrameworkServlet 'dispatcherServlet': initialization started
2016-09-10 16:15:39.540 INFO 73606 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : FrameworkServlet 'dispatcherServlet': initialization completed in 16 ms
2016-09-10 16:15:39.598 INFO 73606 --- [nio-8080-exec-1] o.s.i.codec.kryo.CompositeKryoRegistrar : registering [40, java.io.File] with serializer org.springframework.integration.codec.kryo.FileSerializer
2016-09-10 16:15:39.638 ERROR 73606 --- [nio-8080-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.messaging.MessageHandlingException: error occurred in message handler [org.springframework.cloud.stream.binder.rabbit.RabbitMessageChannelBinder$SendingHandler#1b59052b]; nested exception is com.esotericsoftware.kryo.KryoException: java.util.ConcurrentModificationException
Serialization trace:
classes (sun.misc.Launcher$AppClassLoader)
beanClassLoader (org.springframework.context.event.SimpleApplicationEventMulticaster)
applicationEventMulticaster (org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext)
applicationContext (org.activiti.spring.ApplicationContextElResolver)
resolvers (org.activiti.engine.impl.javax.el.CompositeELResolver)
elResolver (org.activiti.engine.impl.el.ActivitiElContext)
cachedElContext (org.activiti.engine.impl.persistence.entity.ExecutionEntity)] with root cause
java.util.ConcurrentModificationException: null
at java.util.Vector$Itr.checkForComodification(Vector.java:1184) ~[na:1.8.0_102]
at java.util.Vector$Itr.next(Vector.java:1137) ~[na:1.8.0_102]
at com.esotericsoftware.kryo.serializers.CollectionSerializer.write(CollectionSerializer.java:92) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.serializers.CollectionSerializer.write(CollectionSerializer.java:40) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.Kryo.writeObject(Kryo.java:552) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.serializers.ObjectField.write(ObjectField.java:80) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.serializers.FieldSerializer.write(FieldSerializer.java:518) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.Kryo.writeObject(Kryo.java:552) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.serializers.ObjectField.write(ObjectField.java:80) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.serializers.FieldSerializer.write(FieldSerializer.java:518) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.Kryo.writeObject(Kryo.java:552) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.serializers.ObjectField.write(ObjectField.java:80) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.serializers.FieldSerializer.write(FieldSerializer.java:518) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.Kryo.writeObject(Kryo.java:552) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.serializers.ObjectField.write(ObjectField.java:80) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.serializers.FieldSerializer.write(FieldSerializer.java:518) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.Kryo.writeClassAndObject(Kryo.java:628) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.serializers.CollectionSerializer.write(CollectionSerializer.java:100) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.serializers.CollectionSerializer.write(CollectionSerializer.java:40) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.Kryo.writeObject(Kryo.java:552) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.serializers.ObjectField.write(ObjectField.java:80) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.serializers.FieldSerializer.write(FieldSerializer.java:518) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.Kryo.writeObject(Kryo.java:552) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.serializers.ObjectField.write(ObjectField.java:80) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.serializers.FieldSerializer.write(FieldSerializer.java:518) ~[kryo-shaded-3.0.3.jar:na]
at com.esotericsoftware.kryo.Kryo.writeObject(Kryo.java:552) ~[kryo-shaded-3.0.3.jar:na]
at
Also I have added following annotations to main class.
#SpringBootApplication
#IntegrationComponentScan
#EnableBinding(MessageChannels.class)

Answer 1

Not sure how to help you, because your use-case is fully unclear, but you have problem with serialization for some unserializable object from the Activiti.
And looks like that one is ActivityExecution instance in the execute() method.
That Activiti-Spring Integration sample does something like this:
Start the process via /start REST endpoint.
That process make a delegation to the Spring Integration via gateway bean - ReceiveTaskActivityBehavior. It's JavaDocs says:
* A receive task is a wait state that waits for the receival of some message.
*
* Currently, the only message that is supported is the external trigger,
* given by calling the {#link RuntimeService#signal(String)} operation.
So, that execute() impl just demonstrates that we can call Spring Integration. The main part remains the same - suspend the process until signal() which is done by the MessageChannels.replies() from the /resume REST endpoint.
Now, explain, please, what you would like to achieve with the Spring Cloud Stream there. Actually both those requests()/replies() in this Activiti sample are input. You initiate something in the app via /start and /resume REST APIs.
Not sure how you have modified that sample, but that is really strange that /start initiates the message sending to the RabbitMQ Binder...