code: public final String getJmsxAppId() {
          int choice = getHdr2().getChoiceField(JsHdr2Access.XAPPID);
          if (choice == JsHdr2Access.IS_XAPPID_EMPTY) {
              return null;
          }
          else if (choice == JsHdr2Access.IS_XAPPID_COMPACT) {
              try {
                  return MfpConstants.JMSXAPPIDS[((Byte) getHdr2().getField(JsHdr2Access.XAPPID_COMPACT)).intValue()];
              } catch (ArrayIndexOutOfBoundsException e) {
                  FFDCFilter.processException(e, "com.ibm.ws.sib.mfp.impl.JsApiHdrsImpl.getJmsxAppId", "1059");
                  return null;
              }
          }
          else {
              return (String) getHdr2().getField(JsHdr2Access.XAPPID_STRINGVALUE);
          }
      }
docs: /*
  Get the JMSXAppId value.
  
  Javadoc description supplied by JsJmsMessage interface.
  
  The value to return depends on the JMF choice in the JMS xappid field in
  the message header. If the choice is EMPTY, the only option is to return
  null. If it is STRINGVALUE, then the value contained is returned as is.
  If the choice is COMPACT then the return String is looked up in a table.