Type converter throws exception for null body

[jamie3_james.archibald]

I have a client that sends a request to a service using activemq.

class Service {

  configure() {

   from("activemq:queue:request")

   .bean(this, "getMyObject");

  }

   public MyObject getMyObject() {

       // do a database query and look for the object, return null if we can't find the object

       return null;

   }

}

class MyObject implements Serializable {

}

MyObject result = template.requestBody("activemq:queue:request?jmsMessageType=Object", new MyObject(), MyObject.class);

I receive this exception No type converter available to convert from type: null to the required type: java.io.Serializable with value null.

This used to work when jmsMessageType=Text (as my class is generated using jaxb) however I recently switched over to use Object instead for performance.

[davsclaus]

Can you post the stacktrace? And what version of Camel are you using?

[jamie3_james.archibald]

Here's the stack trace from my unit test.  Camel 2.8.0

org.apache.camel.RuntimeCamelException: org.springframework.jms.MessageFormatException: No type converter available to convert from type: null to the required type: java.io.Serializable with value null; nested exception is javax.jms.MessageFormatException: No type converter available to convert from type: null to the required type: java.io.Serializable with value null

     at org.apache.camel.util.ObjectHelper.wrapRuntimeCamelException(ObjectHelper.java:1145)[camel-core-2.8.0.jar:2.8.0]

     at org.apache.camel.component.jms.EndpointMessageListener.onMessage(EndpointMessageListener.java:143)[camel-jms-2.7.0.jar:2.7.0]

     at org.springframework.jms.listener.AbstractMessageListenerContainer.doInvokeListener(AbstractMessageListenerContainer.java:560)[spring-jms-3.0.5.RELEASE.jar:3.0.5.RELEASE]

     at org.springframework.jms.listener.AbstractMessageListenerContainer.invokeListener(AbstractMessageListenerContainer.java:498)[spring-jms-3.0.5.RELEASE.jar:3.0.5.RELEASE]

     at org.springframework.jms.listener.AbstractMessageListenerContainer.doExecuteListener(AbstractMessageListenerContainer.java:467)[spring-jms-3.0.5.RELEASE.jar:3.0.5.RELEASE]

     at org.springframework.jms.listener.AbstractPollingMessageListenerContainer.doReceiveAndExecute(AbstractPollingMessageListenerContainer.java:325)[spring-jms-3.0.5.RELEASE.jar:3.0.5.RELEASE]

     at org.springframework.jms.listener.AbstractPollingMessageListenerContainer.receiveAndExecute(AbstractPollingMessageListenerContainer.java:263)[spring-jms-3.0.5.RELEASE.jar:3.0.5.RELEASE]

     at org.springframework.jms.listener.DefaultMessageListenerContainer$AsyncMessageListenerInvoker.invokeListener(DefaultMessageListenerContainer.java:1058)[spring-jms-3.0.5.RELEASE.jar:3.0.5.RELEASE]

     at org.springframework.jms.listener.DefaultMessageListenerContainer$AsyncMessageListenerInvoker.executeOngoingLoop(DefaultMessageListenerContainer.java:1050)[spring-jms-3.0.5.RELEASE.jar:3.0.5.RELEASE]

     at org.springframework.jms.listener.DefaultMessageListenerContainer$AsyncMessageListenerInvoker.run(DefaultMessageListenerContainer.java:947)[spring-jms-3.0.5.RELEASE.jar:3.0.5.RELEASE]

     at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)[:1.6.0_26]

     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)[:1.6.0_26]

     at java.lang.Thread.run(Thread.java:662)[:1.6.0_26]

[davsclaus]

He you have a mix of Camel versions. camel-core 2.8.0 and camel-jms 2.7.0

When you do request/reply over JMS with JMS objects, the Camel expect that there is a reply message that can be converted to Serializable. To be send back as the reply.

To indicate an "empty" response you may consider sending back a MyObject having some state that its a "empty" response.

What is your use case? What would you expect to happen when there is no reply body to send back?

[jamie3_james.archibald]

I checked by classpath and it looks like I am using camel-jms 2.7.0, not sure why maven did this. I just explicitly set camel-jms 2.8.0.

I don't think it would be best practise to introduce a flag into all my objects on whether it exists or not. Ideally I would just return null.

Here is an example of why I want to return null. If it can't be done I can probably just switch back to using jmsMessageType=Text for now:

class MyServiceImpl implements IMyService {

   configure() {

     from("activemq:queue:request")

     .bean(this, "getMyObject")

   }

   MyObject getMyObject(@Body String name) {

      // look in database for the object, if it doesnt exist return null

   }

}

class MyClient implements IMyClient {

     MyObject getMyObject(String name) {

       return template.requestBodyAndHeader("activemq:queue:request", name, MyObject.class)

    }

}

public static void main() {

    // our client that interacts with the service via activemq

    // the service is deployed somewhere on the network

   MyClient client = new MyClient();

   MyObject obj = client.getMyObject("Me");

   if (obj == null) {

       // do something

   }

}

[njiang]

I think the camel-jms 2.7.0 dependency is introduced by activemq-camel module. you need to specify the dependency of camel-jms 2.8.0 in your pom to override it.

[davsclaus]

Hi

Keep an eye on this ticket

https://issues.apache.org/jira/browse/CAMEL-3354

To support null return values from beans.

[davsclaus]

Beans already support returning null values.

I created a ticket for the JMS req/reply with null values.

https://issues.apache.org/jira/browse/CAMEL-4384

It works fine on trunk.

[jamie3_james.archibald]

Excellent thanks!

For now I will just use jmsMessageType=Text and switch to Object when the bug has been resolved.

Much thanks