时间简码-java

java里的时间类是比较简单的，如果没有对时间相关类总结学习过，有些需求或许不能立即写出来。现做几个简单的时间编码方法，供以后参考查阅。

//获取距离当天前三个月的日期
{
    Calendar calendar = Calendar.getInstance();
    calendar.add(Calendar.MONTH, -3);
    SimpleDateFormat format = new SimpleDateFormat("yyyyMMdd");        
    String predate = format.format(calendar.getTime());
    Date now = new Date();
    SimpleDateFormat nformat = new SimpleDateFormat("yyyyMMdd");
    String nowdate = nformat.format(now);
    System.out.println(predate+";"+nowdate);
}

输出：
20130826;20131126

//日期date是星期几
int getWeekNum(Date date){
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(date);
    int num = calendar.get(Calendar.DAY_OF_WEEK);
    return num==1?7:num-1;
}

输出：
星期一：1
星期二：2
星期三：3
星期四：4
星期五：5
星期六：6
星期日：7

//判断一年是否为闰年
static boolean IsLeapYear(int year){
    return (year % 400 == 0 || year % 4 == 0 && year % 100 != 0);
}
//获得某一年的总天数
static int GetAllDays(int year){
    return (IsLeapYear(year)? 366: 365);
}
//获得某年、某月的最大天数
static int GetMaxDay(int year,int month){
    switch(month)
    {
    case 1:
    case 3:
    case 5:
    case 7:
    case 8:
    case 10:
    case 12:
                return 31;        
    case 4:
    case 6:
    case 9:
    case 11:
        return 30;    
    case 2:
        return (IsLeapYear(year)? 29: 28);    
    default:
        return -1;
    }
}
//获得某年、某月、某日是这一年的第几天
static int GetDays(int year,int month,int day){
    int sum = 0;
    
    for(int i = 1; i < month ; i++){
        sum += GetMaxDay(year,i);
    }
    
    return sum+day;
}
//获得某年某月某日的下一天
static void GetNextDay(int year,int month,int day){
    if(day != GetMaxDay(year,month)){
        day++;
    }else
    {
        if(month != 12)
        {month++; day = 1;}
        else
        {year++; month = day =1;}
    }
}
//获得某年某月某日的前一天
static void GetPreDay(int year,int month,int day){
    if(day != 1){
        day--;
    }else{
        if(month != 1){
            month--;
            GetMaxDay(year,month);
        }
        else{
            year--;month = 12;day = 31;
        }
    }
}
//获得某年某月某日n天之后的日期
static void GetXDay(int year,int month,int day,int X){
    for(int i = 1; i<= X; i++){
        if(day != GetMaxDay(year,month)){
            day++;
        }else{
            if(month != 12){
                month++;day = 1;
            }else{
                year++;
                month = day = 1;
            }
        }
    }
    System.out.println(X+" 天后是："+year+"-"+month+"-"+day);
    
        
}
//比较日期大小
static int CompareDay(int year1,int month1,int day1, int year2,int month2,int day2){
    return year1 != year2? (year1-year2):(month1 != month2 ? (month1-month2): day1-day2);
}
//求日期之差
static int GetDateDiff1(int year1,int month1,int day1,int year2,int month2,int day2){
    int sum = GetAllDays(year1) - GetDays(year1,month1,day1);
    for(int i = year1+1; i < year2; i++ ){
        sum += GetAllDays(i);
    }
    sum += GetDays(year2,month2,day2);
    return sum;
}
static int GetDateDiff(int year1,int month1,int day1,int year2,int month2,int day2){
        if(CompareDay(year1,month1,day1,year2,month2,day2) > 0){
        return -GetDateDiff1(year2,month2,day2,year1,month1,day1);
    }else if(CompareDay(year1,month1,day1,year2,month2,day2) < 0){
        return GetDateDiff1(year1,month1,day1,year2,month2,day2);
    }
    return 0;
}        

//指定时间距离当前时间
String getAwayTime(long time){
    Calendar calendar = Calendar.getInstance();
    long awaytime = calendar.getTimeInMillis()-time;
    if(awaytime/1000 < 60){
        return "不到1分钟!";
    }
    if(awaytime/1000/60 < 60){
        return awaytime/1000/60+"分钟前！";
    }
    if(awaytime/1000/60/60 < 24){
        return awaytime/1000/60/60+"小时前！";
    }
    return awaytime/1000/60/60/24+"天前！";
}

    /**
     * 获取当前日期 
     * 如 20120412
     * 
     */
    public static String getCurrDate(){
        SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
        return sdf.format(new Date());
    }
    /**
     * 获取当前年份 
     * 如 2012
     * 
     */
    public static String getCurrDate(){
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy");
        return sdf.format(new Date());
    }