java 日期计算

    /**     * 根据起期和期限计算止期     * @param startDate 起期（格式为yyyy-MM-dd）     * @param date 天数或者月数或者年数     * @param dayOrMonth （传"day"或者"month"或者"year"）     * @return     * @throws ParseException     */    public static String calculateDate(String startDate, int date, String dayOrMonth) throws ParseException {        SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd");        Calendar calendar = Calendar.getInstance();        calendar.setTime(sf.parse(startDate));        if ("year".equals(dayOrMonth))            calendar.add(Calendar.YEAR, date);        else if ("month".equals(dayOrMonth))            calendar.add(Calendar.MONTH, date);        else            calendar.add(Calendar.DAY_OF_YEAR, date);        return sf.format(calendar.getTime());    }

执行：calculateDate("2017-08-20", 2, "month")
结果：2017-10-20

    /**     * 日期比较     * @param time1 日期1（格式为yyyy-MM-dd）     * @param time2 日期2（格式为yyyy-MM-dd）     * @return 日期1在日期2之前 true; 日期1在日期2之前 false      * @throws ParseException      */    public static boolean compareDate(String time1, String time2) throws ParseException {        boolean flag = false;        SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");        Date date1 = df.parse(time1);        Date date2 = df.parse(time2);        if (date1.before(date2))            flag = true;        return flag;    }

执行：compareDate("2017-01-15", "2017-02-20")
结果：true

方法1:

    /**     * 判断当前系统时间是否在当天的6点之后     * @return true-是  false-否     */    private static boolean compareDate(){        boolean flag = false;        //当前系统时间        SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");        String currentDateStr = df.format(new Date());        String yyyyMMdd = currentDateStr.split(" ")[0];//      String hour = "";//配置成配置项//      if (StringUtils.isEmpty(hour)) {//          hour = "06";//      } else {//          hour = hour.replace(" ", "");//      }//      int hours;//      try {//          hours = Integer.parseInt(hour);//      } catch (Exception e) {//          hours = 6;//      }//      if(hours < 0 || hours >= 24) hour = "06";//      String appointDateStr = yyyyMMdd + " " + hour + ":00:00";//      String HHmmss = "06:00:00"; //配置成配置项//      SimpleDateFormat df2 = new SimpleDateFormat("HH:mm:ss");//      try {//          df2.parse(HHmmss);//      } catch (ParseException e1) {//          HHmmss = "06:00:00";//      }        String HHmmss = "";        try {            SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");            Calendar calendar  = Calendar.getInstance();            calendar.set(Calendar.HOUR_OF_DAY, 6);            calendar.set(Calendar.SECOND, 0);            calendar.set(Calendar.MINUTE, 0);            HHmmss = sdf.format(calendar.getTime());        } catch (Exception e) {            HHmmss = "06:00:00";        }        String appointDateStr = yyyyMMdd + " " + HHmmss;        try {            Date currentDate = df.parse(currentDateStr);            Date appointDate = df.parse(appointDateStr);            if (currentDate.after(appointDate)) {                flag = true;            }        } catch (ParseException e) {            //打印日志：转换日期异常        }        return flag;    }

方法2：（推荐这种方式）

    /**     * 判断当前系统时间是否在当天的6点之后     * @return true-是  false-否     */    private static boolean compareDate(){        boolean flag = false;        //当前系统时间        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");        String currentDateStr = sdf.format(new Date());//当前日期        try {            Calendar calendar = Calendar.getInstance();            calendar.set(Calendar.HOUR_OF_DAY, 6);//配置成配置项            calendar.set(Calendar.SECOND, 0);//配置成配置项            calendar.set(Calendar.MINUTE, 0);//配置成配置项            String appointDateStr = sdf.format(calendar.getTime());//指定日期            Date currentDate = sdf.parse(currentDateStr);            Date appointDate = sdf.parse(appointDateStr);            if (currentDate.after(appointDate)) {                flag = true;            }        } catch (ParseException e) {            //打印日志：转换日期异常        } catch (Exception e) {            //打印日志：转换日期异常        }        return flag;    }

    /**     * 当前日期与指定日期相差天数     */    private static int days(Date currentDate, Date appointDate) {        int days = (int) ((currentDate.getTime() - appointDate.getTime()) / (1000*3600*24));        return days;    }    //main方法验证    public static void main(String[] args) {        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");        String appointDateStr = "2012-06-17 00:00:00";        String currentDateStr = sdf.format(new Date());        currentDateStr = currentDateStr.split(" ")[0] + " 00:00:00";        try {            Date appointDate = sdf.parse(appointDateStr);            Date currentDate = sdf.parse(currentDateStr);            int days = days(currentDate, appointDate);            System.out.println(days);        } catch (ParseException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }    }