ModuleData.getPrincipalData returns null in the adapter module development

Question

Hi gurus,
i am doing a test on the adapter module development following an article written by William Li:
http://www.sdn.sap.com/irj/scn/go/portal/prtroot/docs/library/uuid/f0ac06cf-6ee2-2c10-df98-e17430ca5949?QuickLink=index&overridelayout=true
my problem is after the EJB has been deployed, it seems that the return of inputModuleData.getPrincipalData() is always null which makes the program can not get the xml payload from the framework.
the main process of the example has been simplified like this:
     public ModuleData process(ModuleContext moduleContext, ModuleData inputModuleData) throws ModuleException {
          Object           obj = null;
          try {
          obj = inputModuleData.getPrincipalData();
          Message     msg1 = (Message) obj;          
                XMLPayload xmlpayload = msg1.getDocument();}          
          catch (Exception e) {
               ModuleException me = new ModuleException(e);
               throw me;
          return inputModuleData;
after deployed, i get the following error in the adapter monitor of RWB: (my JNDI is testtest)
17.02.2012 17:13:44.643 Information Send binary file  "test8.xml" from FTP server "10.18.48.150:/encrypt_test/", size 206 bytes with QoS EO
17.02.2012 17:13:44.644 Information MP: processing local module localejbs/CallSapAdapter
17.02.2012 17:13:44.644 Information Application attempting to send an XI message asynchronously using connection File_http://sap.com/xi/XI/System
17.02.2012 17:13:44.645 Information Trying to put the message into the send queue
17.02.2012 17:13:44.648 Information MP: processing local module localejbs/testtest
17.02.2012 17:13:44.648 Error MP: exception caught with cause java.lang.NullPointerException: while trying to invoke the method com.sap.engine.interfaces.messaging.api.Message.getDocument() of an object loaded from local variable 'msg1'
whereas if the code has been changed like this:
     public ModuleData process(ModuleContext moduleContext, ModuleData inputModuleData) throws ModuleException {
          Object           obj = null;
          try {
               obj = inputModuleData.getPrincipalData();
               Message     msg1 = (Message) obj;     
               if (obj != null )
                    XMLPayload xmlpayload = msg1.getDocument();
          catch (Exception e) {
               ModuleException me = new ModuleException(e);
               throw me;
          return inputModuleData;
the file can be read by the file adapter.
i just quite confused that why the return of the getPrincipalData() is null? where is the problem? thanks
Edited by: Stephen Xue on Feb 17, 2012 5:22 AM

Answer 1

I'm gonna reply to myself here. I changed the processing sequence of the adapter modules in the  in the FileSender channel so that my module comes first then CallSapAdapter. Then getPrincipalData() contains the message.
Hope this helps someone else.