public String findPreviousComment(String taskId) {
        Task task = null;
        Map<Integer, String> pList = new HashMap<>();

        task = taskService.createTaskQuery()//
                .taskId(taskId)//使用任務ID查詢
                .singleResult();

        if (task == null) {
            throw new ServiceException("任務不存在");
        }
        String processInstanceId = task.getProcessInstanceId();
        List<HistoricTaskInstance> list = historyService//與歷史資料（歷史表）相關的service
                .createHistoricTaskInstanceQuery()//建立歷史任務例項查詢
                .processInstanceId(processInstanceId)
                .list();
        logger.info("上一節點任務ID：{}" + list.get(list.size() - 2).getId());
        List<Comment> commentList = taskService.getTaskComments(list.get(list.size() - 2).getId());
        if (commentList.size()>0) {
            return commentList.get(0).getFullMessage();
        }else {
            return "";
        }
    }