Java Calendar需要注意的坑-优快云博客

本文链接：https://blog.youkuaiyun.com/zilenge3728/article/details/102714513

1、获得星期几

    private String getDayOfWeek(Date date){
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        int dayOfWeek = calendar.get(Calendar.DAY_OF_WEEK)-1;
        return dayOfWeek==0?"星期日":"星期"+dayOfWeek;
    }

根据源码显示，一周是从星期日开始，所以星期日到星期六依次对应的是1-7，
应该对获得的int减一，即为星期数，0的话就是星期天。

    public final static int SUNDAY = 1;
    public final static int MONDAY = 2;
    public final static int TUESDAY = 3;
    public final static int WEDNESDAY = 4;
    public final static int THURSDAY = 5;
    public final static int FRIDAY = 6;
    public final static int SATURDAY = 7;

2、获得月份

    private int getMonthOfYear(Date date){
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        return calendar.get(Calendar.MONTH)+1;
    }

    public final static int JANUARY = 0;
    public final static int FEBRUARY = 1;
    public final static int MARCH = 2;
    public final static int APRIL = 3;
    public final static int MAY = 4;
    public final static int JUNE = 5;
    public final static int JULY = 6;
    public final static int AUGUST = 7;
    public final static int SEPTEMBER = 8;
    public final static int OCTOBER = 9;
    public final static int NOVEMBER = 10;
    public final static int DECEMBER = 11;

如源码所示，直接加1即可。

3、获取WEEK_OF_YEAR和WEEK_OF_MONTH

在获取WEEK_OF_YEAR和WEEK_OF_MONTH的时候，记得把一个星期的开始设为星期一，默认是星期天。另外还有一点需要提到，可以根据业务的需求，判断一个月开始的那几天算不算一周，默认是1。

    private int getWeekOfYear(Date date){
        Calendar calendar = Calendar.getInstance();
        calendar.setFirstDayOfWeek(Calendar.MONDAY);
        //calendar.setMinimalDaysInFirstWeek(1);
        calendar.setTime(date);
        return calendar.get(Calendar.WEEK_OF_YEAR);
    }