When executing a BatchCommand with a custom data model, the kie-server should interpret the header x-kie-contenttype with a value of XSTREAM;ignore-unknown-elements=true to ignore any additional elements in the data-model as mentioned in issue JBPM-9558.

We need this behaviour because we need a loose coupling between the kie-client and the kie-server. If the client gets updated with a new version of the data model, the server should consume data structures created with the an older version ignoring any new fields.

The XStreamMarshaller has an overloaded unmarshall() function which can handle the parameter mentioned above. Unfortunately this method is not used in case of BatchCommand execution. In this case, the default implementation is used which hardcodes the value to false:

public <T> T unmarshall(String input, Class<T> type)
{ return unmarshall(input, type, Collections.singletonMap(XSTREAM_IGNORE_UNKNOWN, false)); }

Setting the default to "true" solves the problem for us but this may not be the desired solution.

Using the MarshallingFormat.buildParameters() to extract the parameter and passing those parameters to XStreamMarshaller.unmarshall() seems to be the right way to do it. Therefore the KieServerResource.executeCommands() function must be extended to pass the parameters from the header to the underlying layers:

ServiceResponsesList result = delegate.executeScript(command, MarshallerHelper.getFormat(contentType), null);

See https://github.com/comlinegmbh/kie-server-xstream-fieldparsing-poc for a project with a showcase.