date 操作

<%@ page import="java.util.Date"%>  
<%@ page import="java.text.DateFormat"%>  
<%  
Date dNow = new Date();  
  
SimpleDateFormat formatter = new SimpleDateFormat("E yyyy.MM.dd 'at' hh:mm:ss a zzz");  
out.println("It is " + formatter.format(dNow));  
%>  
  
输出的结果为：  
It is 星期五 2003.05.30 at 11:30:46 上午 CST   
(更为详尽的格式符号请参看SimpleDateFormat类)  
  
6、将字符串转换为日期  
<%@ page import="java.util.Date"%>  
<%@ page import="java.text.DateFormat"%>  
<%  
String input = "1222-11-11";  
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");  
Date t = null;  
try{  
t = formatter.parse(input);  
out.println(t);  
}catch(ParseException e){  
out.println("unparseable using " + formatter);  
}  
%>  
输出结果为：  
Fri Nov 11 00:00:00 CST 1222  
  
7、计算日期之间的间隔  
<%@ page import="java.util.Date"%>  
<%@ page import="java.text.DateFormat"%>  
<%  
String input = "2003-05-01";  
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");  
Date d1 = null;  
try{  
d1 = formatter.parse(input);  
}catch(ParseException e){  
out.println("unparseable using " + formatter);  
}  
  
Date d2 = new Date();  
  
long diff = d2.getTime() - d1.getTime();  
out.println("Difference is " + (diff/(1000*60*60*24)) + " days.");  
%>  
输出结果为：  
Difference is 29 days.  
  
8、日期的加减运算  
方法：用Calendar类的add()方法  
<%@ page import="java.util.*"%>  
<%@ page import="java.text.*"%>  
<%  
Calendar now = Calendar.getInstance();  
SimpleDateFormat formatter = new SimpleDateFormat("E yyyy.MM.dd 'at' hh:mm:ss a zzz");  
out.println("It is now " + formatter.format(now.getTime()));  
now.add(Calendar.DAY_OF_YEAR,-(365*2));  
out.println("<br>");  
out.println("Two years ago was " + formatter.format(now.getTime()));  
%>  
输出结果为：  
It is now 星期五 2003.05.30 at 01:45:32 下午 CST   
Two years ago was 星期三 2001.05.30 at 01:45:32 下午 CST  
  
9、比较日期  
方法：用equals()、before()、after()方法  
<%@ page import="java.util.*"%>  
<%@ page import="java.text.*"%>  
<%  
DateFormat df = new SimpleDateFormat("yyy-MM-dd");  
Date d1 = df.parse("2000-01-01");  
Date d2 = df.parse("1999-12-31");  
  
String relation = null;  
if(d1.equals(d2))  
relation = "the same date as";  
else if(d1.before(d2))  
relation = "before";  
else  
relation = "after";  
out.println(d1 +" is " + relation + ' ' + d2);  
%>  
输出结果为：  
Sat Jan 01 00:00:00 CST 2000 is after Fri Dec 31 00:00:00 CST 1999  
  
10、记录一件事所花费的时间  
方法：调用两次System.getTimeMillis()方法，求差值  
<%@ page import="java.text.*"%>  
<%  
long t0,t1;  
t0 = System.currentTimeMillis();  
out.println("Cyc starts at " + t0);  
int k = 0;  
for(int i =0;i<100000;i++){  
k += i;  
}  
t1 = System.currentTimeMillis();  
out.println("<br>");  
out.println("Cyc ends at " + t1);  
out.println("<br>");  
out.println("This run took " + (t1-t0) + "ms.");  
%>  
  
输出结果为：  
Cyc starts at 1054275312432   
Cyc ends at 1054275312442   
This run took 10ms.  
  
其它：如何格式化小数  
  
<%@ page import="java.text.*"%>  
<%  
DecimalFormat df = new DecimalFormat(",###.00");  
double aNumber = 33665448856.6568975;  
String result = df.format(aNumber);  
out.println(result);  
%>  
  
输出结果为：  
33,665,448,856.66  
  
  
======================  
  
日期比较：  
  
在JAVA中日期的计算与比较可以使用Date和DateFormat来解决，下面是一段示例代码：  
  
import java.text.*;  
import java.util.*;  
  
public class Test{  
  
　public static void main(String[] args){  
　　try{  
　　　Date date=new Date();  
　　　DateFormat df=DateFormat.getDateTimeInstance();  
　　　String now=df.format(date);   
　　　System.out.println("现在时间:"+now);  
  
　　　System.out.println("现在时间是否在16:00之前:"+date.before(df.parse("2004-12-24 16:00:00")));   
　　}  
　　catch(ParseException e){System.out.print(e.getMessage());  
　　}  
　}  
}