If you rename:
@RequestParam(value = ServiceConstants.GENERATED_BY_PARAM, required = false) String activityId,
to
@RequestParam(value = ServiceConstants.GENERATED_BY_PARAM, required = false) String generatedBy,
The javadoc will be correct.  The rename will not be a breaking api change and you would not need to tell the caller to use a different name than what gets auto-documented.