Get IDoc-number from flat IDoc using dynamic configuration

Question

Dear experts
In an IDoc2File scenario I have added the IDoc-number to dynamic configuration using the folling code in an UDF:
DynamicConfiguration conf = (DynamicConfiguration)
container.getTransformationParameters().get(StreamTransformationConstants.DYNAMIC_CONFIGURATION);
DynamicConfigurationKey FileName = DynamicConfigurationKey.create("http:/"+"/sap.com/xi/XI/System/File","DOCNUM");
conf.put(FileName, a);
The information is stored in the SOAP message
<SAP:DynamicConfiguration SOAP:mustUnderstand="1">
  <SAP:Record namespace="http://sap.com/xi/XI/System/File" name="DOCNUM">0000000000012345</SAP:Record>
</SAP:DynamicConfiguration>
Can anybody tell me how I can access this information in the "variable substitution" section of the CC? Perhaps something like "message:docnum"?
Additional information:
Taking the IDoc-number from the payload using e.g. "payload:ORDERS05,1,IDOC,1,EDI_DC40,1,DOCNUM,1" does not work, since the XML-IDoc has been converted to an flat-IDoc.
Thanks in advance for any good ideas
Markus

Answer 1

Dear Rodrigo and Sarvesh
Thanks for your help so far! I applied your hints and now it is working fine.
But now I have the following additional questions
1.) My message mapping only maps the input IDoc to an output IDoc of the same type and structure. The MM is only required to process the UDF. Is there another, better solution to achieve my requirement that the IDoc-number shall be part of the filename?
2.) In the CC you have the possibility to use temporary files (section "Processing", Option "Put File" = "Use Temporary File". I think this will not work with the given solution, will it?
To possibly help somebody else or clarify the mechanism once again, I wrote down how my solution now looks like.
My UDF in the message-mapping looks like this
- Input = DOCNUM of IDoc, e.g. ORDERS05/IDOC/EDIDC/DOCNUM
- Outpt = DOCNUM of IDoc, e.g. ORDERS05/IDOC/EDIDC/DOCNUM
- UDF:
public String putDynamicConfiguration(String docnum, Container container) throws StreamTransformationException{
try
     DynamicConfiguration conf = (DynamicConfiguration) container.getTransformationParameters().get(StreamTransformationConstants.DYNAMIC_CONFIGURATION);
     DynamicConfigurationKey key = DynamicConfigurationKey.create("http://sap.com/xi/XI/System/File","FileName");
     String filename = "Prefix_" + docnum + ".txt";
     conf.put(key, filename);
     return docnum;
catch (Exception e)
     return docnum;
In the CC the settings are now as follows
File Name Scheme = . -> only a dot or something else, because this field is obligatory, even if it is not used in this case.
Variable substitution (...)
    Enable -> unchecked
Adapter-Specific Message Attributes
    Use Adapter-Specific Message Attributes -> checked
    Fail If Adapter-Specific Message Attributes Missing -> checked
    File Name -> checked
    Directory, File Type, Temporary Name Scheme for Target File Name -> unchecked
When I send an IDoc to PI and view the Adapte-Engine Version of the message (the SOAP-document, not the payload) I can find the Filename:
<SAP:DynamicConfiguration SOAP:mustUnderstand="1">
<SAP:Record namespace="http://sap.com/xi/XI/System/File" name="FileName">Prefix_0000000000012345.txt</SAP:Record>
</SAP:DynamicConfiguration>