Mule ESB choice flow control route - soap

Question

In Mule I have the following flow :
there is a choice flow control which test the input and verify if the input String equals 'ctr1'.
<flow name="mediationFlow1" doc:name="mediationFlow1">
<file:inbound-endpoint path="C:\MuleStudio\SandBox\input" pollingFrequency="3000" responseTimeout="10000" doc:name="File"/>
<file:file-to-string-transformer doc:name="File to String"/>
<choice doc:name="Choice">
<when expression="payload=='ctr1'">
<cxf:jaxws-client operation="find" serviceClass="services.port.PortWS" port="portWSPort" enableMuleSoapHeaders="true" doc:name="Port"/>
<http:outbound-endpoint exchange-pattern="request-response" method="POST" address="http://localhost:8080/Actors/portWS" doc:name="portWS"/>
</when>
<otherwise >
<cxf:jaxws-client operation="find" serviceClass="services.douane.DouaneWS" port="douaneWSPort" enableMuleSoapHeaders="true" doc:name="Douane"/>
<http:outbound-endpoint exchange-pattern="request-response" method="POST" address="http://localhost:8080/Actors/douaneWS" doc:name="douaneWS"/>
</otherwise>
</choice>
<file:outbound-endpoint path="C:\MuleStudio\SandBox\output" outputPattern="#[function:datestamp:dd-MM-yy]_#[function:systime].xml " responseTimeout="10000" doc:name="Outgoing File"/>
</flow>
</mule>
the both web services call works perfectly when I run them speratly, but when I add the choice ccontrol this is what I got :
INFO 2013-05-14 15:48:07,892 [[mediation].connector.file.mule.default.receiver.01] org.mule.transport.file.FileMessageReceiver: Lock obtained on file: C:\MuleStudio\SandBox\input\input.txt
INFO 2013-05-14 15:48:08,206 [[mediation].mediationFlow1.stage1.02] org.mule.transport.service.DefaultTransportServiceDescriptor: Loading default outbound transformer: org.mule.transport.http.transformers.ObjectToHttpClientMethodRequest
INFO 2013-05-14 15:48:08,216 [[mediation].mediationFlow1.stage1.02] org.mule.transport.service.DefaultTransportServiceDescriptor: Loading default response transformer: org.mule.transport.http.transformers.MuleMessageToHttpResponse
INFO 2013-05-14 15:48:08,253 [[mediation].mediationFlow1.stage1.02] org.mule.transport.service.DefaultTransportServiceDescriptor: Loading default outbound transformer: org.mule.transport.http.transformers.ObjectToHttpClientMethodRequest
INFO 2013-05-14 15:48:08,254 [[mediation].mediationFlow1.stage1.02] org.mule.lifecycle.AbstractLifecycleManager: Initialising: 'connector.http.mule.default.dispatcher.7073225'. Object is: HttpClientMessageDispatcher
INFO 2013-05-14 15:48:08,260 [[mediation].mediationFlow1.stage1.02] org.mule.lifecycle.AbstractLifecycleManager: Starting: 'connector.http.mule.default.dispatcher.7073225'. Object is: HttpClientMessageDispatcher
INFO 2013-05-14 15:48:09,035 [[mediation].connector.file.mule.default.dispatcher.01] org.mule.lifecycle.AbstractLifecycleManager: Initialising: 'connector.file.mule.default.dispatcher.23051110'. Object is: FileMessageDispatcher
INFO 2013-05-14 15:48:09,035 [[mediation].connector.file.mule.default.dispatcher.01] org.mule.lifecycle.AbstractLifecycleManager: Starting: 'connector.file.mule.default.dispatcher.23051110'. Object is: FileMessageDispatcher
INFO 2013-05-14 15:48:09,040 [[mediation].connector.file.mule.default.dispatcher.01] org.mule.transport.file.FileConnector: Writing file to: C:\MuleStudio\SandBox\output\14-05-13_1368539289037.xml
INFO 2013-05-14 15:48:09,043 [[mediation].connector.file.mule.default.dispatcher.01] org.mule.module.xml.transformer.jaxb.JAXBContextResolver: No common Object of type 'class javax.xml.bind.JAXBContext' configured, creating a local one for: SimpleDataType{type=services.port.Port, mimeType='text/xml'}, SimpleDataType{type=java.io.InputStream, mimeType='*/*'}
ERROR 2013-05-14 15:48:09,058 [[mediation].connector.file.mule.default.dispatcher.01] org.mule.exception.DefaultMessagingExceptionStrategy:
********************************************************************************
Message : An invalid return type "class java.io.InputStream" was specified for transformer "JAXBMarshallerTransformer"
Code : MULE_ERROR-266
--------------------------------------------------------------------------------
Exception stack is:
1. An invalid return type "class java.io.InputStream" was specified for transformer "JAXBMarshallerTransformer" (org.mule.api.transformer.TransformerException)
org.mule.module.xml.transformer.jaxb.JAXBMarshallerTransformer:122 (http://www.mulesoft.org/docs/site/current3/apidocs/org/mule/api/transformer/TransformerException.html)
--------------------------------------------------------------------------------
Root Exception stack trace:
org.mule.api.transformer.TransformerException: An invalid return type "class java.io.InputStream" was specified for transformer "JAXBMarshallerTransformer"
at org.mule.module.xml.transformer.jaxb.JAXBMarshallerTransformer.doTransform(JAXBMarshallerTransformer.java:122)
at org.mule.transformer.AbstractTransformer.transform(AbstractTransformer.java:411)
at org.mule.DefaultMuleMessage.getPayload(DefaultMuleMessage.java:362)
+ 3 more (set debug level logging or '-Dmule.verbose.exceptions=true' for everything)
********************************************************************************
I'm not sure if it's coming from the choice test expression?
Although I cant find much informations on how to use the choice control flow in details.

Answer 1

Mule by default applies lot of transformers in the flow to convert the payload to required formats.
In the case when there is no choice router it converts the object returned into an xml string to write to file.
But with choice router it is the programmers responsibility to provide a transformer to convert the response object to an XML string.
Add the following mule-xml jaxb object to xml transformer after choice router and before writing to file-outbound.
.....
</otherwise>
</choice>
<xm:jaxb-object-to-xml-transformer name="ObjectToXML" jaxbContext-ref="MyJaxb" returnClass="java.lang.String" encoding="UTF-8"/>
Hope this helps.