java中用Calendar获取各个阶段时间

  /**
     * 获取当年第一天
     * @return
     */
    private String getCurentYearFistDay(){
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat(DateFormatUtils.DATE_DAY_FORMATE);
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.DAY_OF_YEAR,1);
        log.info("获取当年第一天={}" , simpleDateFormat.format(calendar.getTime()));
        return simpleDateFormat.format(calendar.getTime());
    }

    /**
     * 获取当月第一天
     * @return
     */
    private String getCurentMonthFistDay(){
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat(DateFormatUtils.DATE_DAY_FORMATE);
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.DAY_OF_MONTH,1);
        log.info("获取当月第一天={}" , simpleDateFormat.format(calendar.getTime()));
        return simpleDateFormat.format(calendar.getTime());
    }

    /**
     * 获取今天最早时间
     * @return
     */
    private String getTodayFistTime(){
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat(DateFormatUtils.DATE_DAY_FORMATE);
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.HOUR_OF_DAY,0);
        log.info("获取今天最早时间={}" , simpleDateFormat.format(calendar.getTime()));
        return simpleDateFormat.format(calendar.getTime());
    }

    /**
     * 获取昨天最早时间
     * @return
     */
    private String getYesTodayFistTime(){
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat(DateFormatUtils.DATE_DAY_FORMATE);
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.HOUR_OF_DAY,-1);
        log.info("获取昨天最早时间={}" , simpleDateFormat.format(calendar.getTime()));
        return simpleDateFormat.format(calendar.getTime());
    }