code: public Long getRequestId() throws ActivityException {
  
          if (requestId != null)
              return requestId;
  
          String requestIdVarName = getAttribute("requestIdVariable", "requestId");
  
          Variable requestIdVar = getProcessDefinition().getVariable(requestIdVarName);
          if (requestIdVar == null && !"GET".equals(getHttpMethod()))
              throw new ActivityException("Request ID variable not defined: " + requestIdVarName);
  
          Object requestIdObj = getVariableValue(requestIdVarName);
          if (requestIdObj == null)
              return null;
  
          if (requestIdObj instanceof Long) {
              return (Long) requestIdObj;
          }
          else {
              try {
                  return Long.valueOf(requestIdObj.toString());
              }
              catch (NumberFormatException ex) {
                  throw new ActivityException(
                          "Invalid value for " + requestIdVarName + ": " + requestIdObj);
              }
          }
      }
docs: Returns the requestId that we will use to populate the serviceSummary
  @return requestId used to populate the serviceSummary