使用日期操作类（Calendar）获得几秒、几分钟、几小时之前的时间

public String dealDate(String case_time){
        // 日期操作类
        Calendar calendar = Calendar.getInstance();
        // 当前时间
        calendar.setTime(new Date());
        SimpleDateFormat sdf = new SimpleDateFormat(
                "yyyy-MM-dd HH:mm");
        if(case_time.contains("秒")){
            int parseInt = Integer.parseInt(case_time.replaceAll("秒前", ""));
            calendar.add(Calendar.SECOND, -parseInt);
            case_time = sdf.format(calendar.getTime()); 
        }else if(case_time.contains("分钟")){
            int parseInt = Integer.parseInt(case_time.replaceAll("分钟前", ""));
            calendar.add(Calendar.MINUTE, -parseInt);
            case_time = sdf.format(calendar.getTime());
        }else if(case_time.contains("小时")){
            int parseInt = Integer.parseInt(case_time.replaceAll("小时前", ""));
            calendar.add(Calendar.HOUR, -parseInt);
            case_time = sdf.format(calendar.getTime());
        }
        return case_time;
    }
    
    public static void main(String[] args)
    {
        String dealDate = new InternetWormServiceImpl().dealDate("12秒前");
        System.out.println(dealDate);
    }