Java日期处理

一、简介

二、常见的类

java.util.Date;

java.util.Calender

java.util.GregorianCalendar

java.text.DateFormat

java.text.SimpleDateFormat

三、常见用法

3.1获取当前时间

获取当前时间有两种办法，通过Calender获取还可以获取日期相关信息，比如当前星期几，一年中第几天等

Date currentTime = new Date();
Date currentTime2 = Calender.getInstance().getTime();

备注：currentTime.getTime()获取从1970.01.01 00:00:00到当前时间的总毫秒数

calendar.getTime()获取当前date对象

3.2按照相应格式打印时间

常用时间格式是SimpleDateFormat,它是DateFormat的子类，DateFormat是一个抽象类，它定义了日期格式化的字段和方法

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss")
Date date = new Date();
sdf.format(date);

具体格式字符代表

具体详情请看API

3.3将字符串转换成时间

String time = "2012-10-16";
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
sdf.parse(time);

3.4时间加减

Date today = new Date();
long totalMilisecond = today.getTime()-7*24*60*60*1000;
Date sevenDayBefore = new Date(totalMilisecond );

3.5时间间隔

Date bornDay = new GregorianCalendar(1900,1,1).getTime();
Date today = new Date();
long diff= today.getTime()-bornDay.getTime();
System.out.println(bornDay+":"+today);
System.out.println("you were born total "+diff/(24*60*60*1000)+" day");

3.6比较日期

String[] input ={"2012-10-10","2012-10-11"};
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Date d1 =sdf.parse(input[0]);
Date d2 =sdf.parse(input[1]);
String relation =null ;
if (d1.equals(d2)) {
    relation = " the same as ";
}else if(d1.before(d2)){
    relation =" < ";
}else if(d1.after(d2)){
    relation =" > ";
}
System.out.println(sdf.format(d1) +relation+sdf.format(d2) );

3.7获取当前日期信息

Calendar c = Calendar.getInstance();
System.out.println("year : "+c.get(Calendar.YEAR));
System.out.println("month : "+(c.get(Calendar.MONTH)+1));
System.out.println("day : "+c.get(Calendar.DATE));
System.out.println("day of week : "+c.get(Calendar.DAY_OF_WEEK));
System.out.println("day of month : "+c.get(Calendar.DAY_OF_MONTH));
System.out.println("day of year: "+c.get(Calendar.DAY_OF_YEAR));
System.out.println("week in month : "+c.get(Calendar.WEEK_OF_MONTH));
System.out.println("week in year : "+c.get(Calendar.WEEK_OF_YEAR));
System.out.println("day of week in month : "+c.get(Calendar.DAY_OF_WEEK_IN_MONTH));
System.out.println("Hour : "+c.get(Calendar.HOUR));
System.out.println("AM or PM : "+c.get(Calendar.AM_PM));
System.out.println("Hour of day(24-hour clock) : "+c.get(Calendar.HOUR_OF_DAY));
System.out.println("Minute : "+c.get(Calendar.MINUTE));
System.out.println("Second : "+c.get(Calendar.SECOND));

四、一个日期的小应用

 

public class ReminderService {
    
    Timer timer = new Timer();
    
    public static void main(String[] args) throws IOException {
        new ReminderService().load();
    }
    
    void load() throws IOException{
        BufferedReader bf = new BufferedReader(new FileReader("ReminderService.txt"));
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String aLine;
        while((aLine=bf.readLine())!=null){
            ParsePosition pp = new ParsePosition(0);
            Date date = sdf.parse(aLine, pp);
            if (date == null) {
                message("Invalide date in \" "+aLine+" \"");
                continue;
            }
            String mesg = aLine.substring(pp.getIndex());
            timer.schedule(new Item(mesg), date);
        }
        
    }
    
    class Item extends TimerTask{
        String message;
        
        public Item(String m) {
            this.message=m;
        }
        
        @Override
        public void run() {
            message(message);
        }
        
    }
    
    private void message(String message){
        System.out.println("message: "+message);
        JOptionPane.showMessageDialog(null, message, "Timer Alert", JOptionPane.INFORMATION_MESSAGE);
    }
}