java日期操作整理

1、获取服务器端当前日期：
<%@ page import="java.util.Date"%>
<%
Date myDate = new Date();
%>

2、获取当前年、月、日：

<%@ page import="java.util.Date"%>

<%
Date myDate = new Date();
int thisYear = myDate.getYear() + 1900;//thisYear = 2003
int thisMonth = myDate.getMonth() + 1;//thisMonth = 5
int thisDate = myDate.getDate();//thisDate = 30
%>

3、按本地时区输出当前日期

<%@ page import="java.util.Date"%>
<%
Date myDate = new Date();
out.println(myDate.toLocaleString());
%>

输出结果为：
2003-5-30

4、获取数据库中字段名为"publish_time"、类型为Datetime的值

<%@ page import="java.util.Date"%>
<%
...连接数据库...
ResultSet rs = ...
Date sDate = rs.getDate("publish_time");
%>
[code]

5、按照指定格式打印日期

[code]
<%@ 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;
trycatch(ParseException e)

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++)
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