关于时间

    /**
     * 取得系统当前时间(格式：1970年1月1日0时起到当前的毫秒)
     *
     * @return 当前时间
     */
    public static long getCurrentTiem() {
        return System.currentTimeMillis();
    }

    /**
     * 取得当前时间，格式： yyyy-MM-dd hh:mm:ss
     *
     * @return 当前时间
     */
    public static String getNowTime() {
        Calendar calendar = Calendar.getInstance();
        calendar.setTimeInMillis(new Date().getTime());
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        return dateFormat.format(calendar.getTime());
    }

    /**
     * 字符串(格式：yyyy-MM-dd hh:mm:ss) --> 毫秒(说明：1970年1月1日0时起到当前字符串时间的毫秒)
     *
     * @return 毫秒数(1970年1月1日0时起到当前字符串时间的毫秒)
     */
    public static long stringToMillis(String source) {
        Date date = null;
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        try {
            date = dateFormat.parse(source);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        if(null == date) return 0;
        return date.getTime();
    }
    

    /**
     *  取得当前日期
     */
    public static String nowdate() {
        Calendar c = Calendar.getInstance();
        c.setTimeInMillis(new Date().getTime());
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
        return dateFormat.format(c.getTime());
    }

/**
     *  取得N个月以后的日期
     */
    public static String N_MonthDate(int n) {
        Calendar c = Calendar.getInstance();
        c.add(c.MONTH, n);
        return "" + c.get(c.YEAR) + "-" + (c.get(c.MONTH) + 1) + "-" + c.get(c.DATE);
    }

    /**
     * 
     * @function 计算两个时间的差：耗时多少
     * @param --例子"2004-01-02 11:30:24"
     * @throws ParseException
     */

    public static String getPastTime(String nowtime, String oldtime) throws ParseException {//
        SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        java.util.Date now = df.parse(nowtime);
        java.util.Date date = df.parse(oldtime);
        long l = now.getTime() - date.getTime();
        long day = l / (24 * 60 * 60 * 1000);
        long hour = (l / (60 * 60 * 1000) - day * 24);
        long min = ((l / (60 * 1000)) - day * 24 * 60 - hour * 60);
        long s = (l / 1000 - day * 24 * 60 * 60 - hour * 60 * 60 - min * 60);
        String pastTime = "" + day + "天" + hour + "小时" + min + "分" + s + "秒";

        return String.valueOf(l);
    }

/**
     * 
     * @function 计算是否过期,true未过期；false过期
     * @throws ParseException
     */

    public static boolean isInvalid(String nowtime, String overtime) throws ParseException {//
        SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        java.util.Date now = df.parse(nowtime);
        java.util.Date over = df.parse(overtime);
        long l = now.getTime() - over.getTime();
        boolean flag = true;
        if (l > 0) {
            flag = false;
        } else {
            flag = true;
        }
        return flag;
    }

/**
     * @desc 取得前一天的时间
     * @param specifiedDay
     * @return
     */
    public static String getDayBefore(String specifiedDay) {
        // SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMdd");
        Calendar c = Calendar.getInstance();
        Date date = null;
        try {
            date = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").parse(specifiedDay);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        c.setTime(date);
        int day = c.get(Calendar.DATE);
        c.set(Calendar.DATE, day - 1);

        String dayBefore = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(c.getTime());
        return dayBefore;
    }

/**
     * @desc 取得后一天的时间
     * @param specifiedDay
     * @return
     */
    public static String getDayAfter(String specifiedDay) {
        Calendar c = Calendar.getInstance();
        Date date = null;
        try {
            date = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").parse(specifiedDay);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        c.setTime(date);
        int day = c.get(Calendar.DATE);
        c.set(Calendar.DATE, day + 1);

        String dayAfter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(c.getTime());
        return dayAfter;
    }

/**
     *
     * @desc 取得前后N天的时间,N=正负数
     * @param specifiedDay
     * @return
     */
    public static String getDayAfterOrBeforeN(String specifiedDay, int N) {
        Calendar c = Calendar.getInstance();
        Date date = null;
        try {
            date = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").parse(specifiedDay);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        c.setTime(date);
        int day = c.get(Calendar.DATE);
        c.set(Calendar.DATE, day + N);

        String dayAfter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(c.getTime());
        return dayAfter;
    }

/**
     * 
     * @desc 取得前后N分钟后的时间,N=正负数
     * @param specifiedDay
     * @return
     */
    public static String getMinuteAfterOrBeforeN(String specifiedDay, int N) {
        Calendar c = Calendar.getInstance();
        Date date = null;
        try {
            date = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").parse(specifiedDay);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        c.setTime(date);
        int minute = c.get(Calendar.MINUTE);
        c.set(Calendar.MINUTE, minute + N);

        String minuteAfter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(c.getTime());
        return minuteAfter;
    }

对于字符串转化成时间，个数要严格的标准，不然会抛出异常

下面提供一个对时间格式的重新封装

String startTime=String.valueOf(map.get("start_time"));//获取时间
Calendar calendar = Calendar.getInstance();
SimpleDateFormat df = new SimpleDateFormat("yyyyMMddHHmmss");//要跟startTime 比如20151124101530的格式一样，不然无法格式化
Date time = null;
try {
    time=df.parse(startTime);
} catch (ParseException e) {
    e.printStackTrace();
}
calendar.setTimeInMillis(time.getTime());
df = new SimpleDateFormat("MM-dd HH:mm");//获取毫秒数，重新转换格式
startTime = df.format(calendar.getTime());
map.put("start_time", startTime);//再封装