Mule ESB Serialization incompatible error - serialization

Question

While making a Service call from Mule 3.2.2 to Mule 3.7.1, i get the following exception.
Though the serialver of org.mule.transformer.types.SimpleDataType class is different on both the runtimes, i'm not sure why this is an issue. Because the Object is anyway serialized to SOAP request.
Any help is appreciated!
Client code in Mule 3.2.2 runtime:
<cxf:jaxws-client serviceClass="org.test" doc:name="SOAP" >
<cxf:ws-security>
<cxf:ws-config>
<cxf:property key="action" value="UsernameToken"/>
<cxf:property key="user" value="test"/>
<cxf:property key="passwordCallbackRef" value-ref="passwordCallbackHandler" />
<cxf:property key="passwordType" value="PasswordText" />
</cxf:ws-config>
</cxf:ws-security>
Exception:
Message : Failed to route event via endpoint: DefaultOutboundEndpoint{endpointUri=https://testlb:17105/service/1.0/, connector=HttpsConnector
{
name=connector.https.mule.default
lifecycle=start
this=60de93b4
numberOfConcurrentTransactedReceivers=4
createMultipleTransactedReceivers=true
connected=true
supportedProtocols=[https]
serviceOverrides=<none>
}
, name='endpoint.https.testlb.17105.service.1.0', mep=REQUEST_RESPONSE, properties={}, transactionConfig=Transaction{factory=null, action=INDIFFERENT, timeout=0}, deleteUnacceptedMessages=false, initialState=started, responseTimeout=60000, endpointEncoding=UTF-8, disableTransportTransformer=false}. Message payload is of type: PostMethod
Code : MULE_ERROR-42999
--------------------------------------------------------------------------------
Exception stack is:
1. org.mule.transformer.types.SimpleDataType; local class incompatible: stream classdesc serialVersionUID = 734974842501135657, local class serialVersionUID = 6394740184248968880 (java.io.InvalidClassException)
java.io.ObjectStreamClass:617 (null)
2. java.io.InvalidClassException: org.mule.transformer.types.SimpleDataType; local class incompatible: stream classdesc serialVersionUID = 734974842501135657, local class serialVersionUID = 6394740184248968880 (org.apache.commons.lang.SerializationException)
org.mule.util.SerializationUtils:89 (null)
3. Failed to route event via endpoint: DefaultOutboundEndpoint{endpointUri=https://testlb:17105/service/1.0/, connector=HttpsConnector
{
name=connector.https.mule.default
lifecycle=start
this=60de93b4
numberOfConcurrentTransactedReceivers=4
createMultipleTransactedReceivers=true
connected=true
supportedProtocols=[https]
serviceOverrides=<none>
}
, name='endpoint.https.testlb.17105.service.1.0', mep=REQUEST_RESPONSE, properties={}, transactionConfig=Transaction{factory=null, action=INDIFFERENT, timeout=0}, deleteUnacceptedMessages=false, initialState=started, responseTimeout=60000, endpointEncoding=UTF-8, disableTransportTransformer=false}. Message payload is of type: PostMethod (org.mule.api.transport.DispatchException)
org.mule.transport.AbstractMessageDispatcher:109 (http://www.mulesoft.org/docs/site/current3/apidocs/org/mule/api/transport/DispatchException.html)
--------------------------------------------------------------------------------
Root Exception stack trace:
java.io.InvalidClassException: org.mule.transformer.types.SimpleDataType; local class incompatible: stream classdesc serialVersionUID = 734974842501135657, local class serialVersionUID = 6394740184248968880
at java.io.ObjectStreamClass.initNonProxy(ObjectStreamClass.java:617)
at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1622)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1517)
+ 3 more (set debug level logging or '-Dmule.verbose.exceptions=true' for everything)

Answer 1

You are absolutely right. It should not be a problem at all. However Java has best practices for serialization - to not mix incompatible classes which look exactly the same serialVersionUID attribute is added to class. Usually developers do not pay attention for it but when they do it means that classes are really different.
It actually means that you cannot use serialization to pass the data. Your case is very good example.
To fix the issue you have to get rid of serialization - this class is different in these two versions of the Mule.
Another option is to substitute class with something more stable. Even create your own SimpleDataType.
Or you can open ticket with Mule support for version incompatibility. However I doubt they will fix it for the same reason - classes are different and it was good reason why they are.

Answer 2

This issue is fixed!
As stated in Mule documentation, session variable from 3.7.1 runtime was wrapped on to SimpleDataType.class and this serialized Base64 encoded string was passed on to the other Runtime as MULE_SESSION header. When the other Runtime deserializes this header, as the class version is different, it throws error.
It's fixed by passing this NullSessionHandler to the HTTP Connector, as we didn't care about that header.
<service-overrides sessionHandler="org.mule.session.NullSessionHandler"/>