java根据年月日判断周几，下面提供四中方法需要的可以参考下.

方法一:

public static String dateToWeek(String datetime) throws java.text.ParseException {

SimpleDateFormat f = new SimpleDateFormat("yyyy-MM-dd");

String[] weekDays = { "星期日", "星期一", "星期二", "星期三", "星期四", "星期五", "星期六" };

Calendar cal = Calendar.getInstance(); // 获得一个日历

Date datet = null;

datet = (Date) f.parse(datetime);

cal.setTime(datet);

int w = cal.get(Calendar.DAY_OF_WEEK) - 1; // 指示一个星期中的某天。

if (w < 0)

w = 0;

System.out.println(weekDays[w]);//星期二

return weekDays[w];

}

public static void main(String[] args) throws java.text.ParseException {

System.out.println(Ts.dateToWeek("2019-01-01"));

}

方法二:

//基姆拉尔森计算公式根据日期判断星期几

public static void CalculateWeekDay(int y, int m, int d) {

if(m < 1 || m >12){

System.out.println("你输入的月份不再范围内，请重新输入！");

}

if (m == 1 || m == 2) {

m += 12;

y--;

}

int iWeek = (d + 2 * m + 3 * (m + 1) / 5 + y + y / 4 - y / 100 + y / 400) % 7;

switch (iWeek) {

case 0:

System.out.printf("星期一\n");

break;

case 1:

System.out.printf("星期二\n");

break;

case 2:

System.out.printf("星期三\n");

break;

case 3:

System.out.printf("星期四\n");

break;

case 4:

System.out.printf("星期五\n");

break;

case 5:

System.out.printf("星期六\n");

break;

case 6:

System.out.printf("星期日\n");

break;

}

}

public static void main(String args[]) {

CalculateWeekDay(2019, 1, 8);

}

方法三：

public static int dayForWeek(String pTime) throws Exception {

SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");

Calendar c = Calendar.getInstance();

c.setTime(format.parse(pTime));

int dayForWeek = 0;

if(c.get(Calendar.DAY_OF_WEEK) == 1){

dayForWeek = 7;

}else{

dayForWeek = c.get(Calendar.DAY_OF_WEEK) - 1;

}

System.out.println(dayForWeek);

return dayForWeek;

}

方法四：

public static String getWeek(Date date){

String[] weeks = {"星期日","星期一","星期二","星期三","星期四","星期五","星期六"};

Calendar cal = Calendar.getInstance();

cal.setTime(date);

int week_index = cal.get(Calendar.DAY_OF_WEEK) - 1;

if(week_index<0){

week_index = 0;

}

System.out.println(weeks[week_index]);

return weeks[week_index];

}

public static void main(String[] args) throws Exception {

Ts.getWeek(new Date());

}

每天积累一点点，总用天会有发光的，加油！！！！