java 时间加减30分钟

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
Date now = new Date();
long time = 30*60*1000;//30分钟
Date afterDate = new Date(now .getTime() + time);//30分钟后的时间
Date beforeDate = new Date(now .getTime() - time);//30分钟前的时间
System.out.println(sdf.format(afterDate ));
System.out.println(sdf.format(beforeDate));