Java Date相关处理

1.获取UTC时间：

        Calendar cal = java.util.Calendar.getInstance();
        // 1 Get offset.
        int zoneOffset = cal.get(java.util.Calendar.ZONE_OFFSET);
        // 2 Get summer offset
        int dstOffset = cal.get(java.util.Calendar.DST_OFFSET);
        // 3 Remove Offset
        cal.add(java.util.Calendar.MILLISECOND, -(zoneOffset + dstOffset));
        // 4 Get UTC time.
        System.out.println("UTC:" + new Date(cal.getTimeInMillis()));

2.自定义Date

        Calendar startCalendar = new GregorianCalendar();
        Calendar endCalendar = new GregorianCalendar();
        startCalendar.setTime(new Date());
        // startCalendar.set(Calendar.MONTH, Calendar.APRIL);
        startCalendar.set(Calendar.MONTH, Calendar.FEBRUARY);
        startCalendar.set(Calendar.HOUR_OF_DAY, 0);
        startCalendar.set(Calendar.MINUTE, 0);
        startCalendar.set(Calendar.SECOND, 0);
        startCalendar.set(Calendar.MILLISECOND, 0);

        endCalendar.setTime(new Date());
        endCalendar.set(Calendar.MONTH, Calendar.FEBRUARY);
        endCalendar.set(Calendar.HOUR_OF_DAY, 23);
        endCalendar.set(Calendar.MINUTE, 59);
        endCalendar.set(Calendar.SECOND, 59);
        endCalendar.set(Calendar.MILLISECOND, 999);
        int a_difference = 0;
        if (a_difference < 0) {
            startCalendar.add(Calendar.MONTH, a_difference);
        }
        else if (a_difference == 0) {
            startCalendar.set(Calendar.DAY_OF_MONTH, 1);
            endCalendar.add(Calendar.MONTH, 1);
            endCalendar.set(Calendar.DAY_OF_MONTH, 0);
        }
        else {
            endCalendar.add(Calendar.MONTH, a_difference);
        }