java

##判断当天为星期几

public int getWeek() {

    SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
    Calendar c = Calendar.getInstance();
    Date date = new Date();
    c.setTime(date);

    String day = format.format(date);
    int currentdayForWeek = 0;

    if (c.get(Calendar.DAY_OF_WEEK) == 1) {
        currentdayForWeek = 7;
    } else {
        currentdayForWeek = c.get(Calendar.DAY_OF_WEEK) - 1;
    }
    return currentdayForWeek;
}

##对List中的某个属性进行排序

###int 类型排序
如List降序

Collections.sort(activities, new Comparator(){
    @Override
    public int compare(Object o1, Object o2) {
         Activities act1 =(Activities)o1;
         Activities act2 =(Activities)o2;
        if(act1.getId()<act2.getId()){
            return 1;
        }else if(act1.getId()==act2.getId()){
            return 0;
        }else{
            return -1;
        }
    }
});

###String 类型排序（字母）
如List studentList升序

Collections.sort(studentList, new Comparator(){
    @Override
    public int compare(Object o1, Object o2) {
        Student stu1 = (Student)o1;
        Student stu2 = (Student)o2;
        return stu1.getName().compareTo(stu2.getName());
    }
});

##java URL编码解码
URLEncoder.encode(“这里是String字符串”, “utf-8”)
URLDecoder.decode(“这里是String字符串”, “utf-8”)

##计算两个日期之间相差的天数

/**
 * 计算两个日期之间相差的天数
 * @param smdate 较小的时间
 * @param bdate  较大的时间
 * @return 相差天数
 * @throws ParseException
 */
public static int daysBetween(Date smdate,Date bdate) throws ParseException
{
    SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
    smdate=sdf.parse(sdf.format(smdate));
    bdate=sdf.parse(sdf.format(bdate));
    Calendar cal = Calendar.getInstance();
    cal.setTime(smdate);
    long time1 = cal.getTimeInMillis();
    cal.setTime(bdate);
    long time2 = cal.getTimeInMillis();
    long between_days=(time2-time1)/(1000*3600*24);

    return Integer.parseInt(String.valueOf(between_days));
}

##java Date
年月日时分秒 对应于数据库 datetime