android 根据日期获取周几

//dateTime为日期
public static String obtainWeek(String dateTime){
    return obtainWeek(dateTime,"yyyyMMdd");
}

public static String obtainWeek(String dateTime,String formatDate){
    String week = "";
    Calendar calendar = Calendar.getInstance();
    //如果日期为空，计算当天是周几
    if (TextUtils.isEmpty(dateTime)){
        calendar.setTime(new Date(System.currentTimeMillis()));
    } else {
        SimpleDateFormat sdf = new SimpleDateFormat(formatDate, Locale.getDefault());
        Date date = null;
        try {
            date = sdf.parse(dateTime);
        } catch (Exception e) {
            Logs.d("callback","时间解析异常");
        }
        if(date != null){
            calendar.setTime(new Date(date.getTime()));
        }
    }

    switch (calendar.get(Calendar.DAY_OF_WEEK)){
        case 1:
            week = "周日";
            break;
        case 2:
            week = "周一";
            break;
        case 3:
            week = "周二";
            break;
        case 4:
            week = "周三";
            break;
        case 5:
            week = "周四";
            break;
        case 6:
            week = "周五";
            break;
        case 7:
            week = "周六";
            break;

    }
    return week;
}