簡單的一些，但基礎的就是要簡單

日期問題
1、獲取服務器端當前日期：
<%@ page import="java.util.Date"%>
<%
Date myDate = new Date();
%>

2、獲取當前年、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、按本地時區輸出當前日期
<%@ page import="java.util.Date"%>
<%
Date myDate = new Date();
out.println(myDate.toLocaleString());
%>
輸出結果為：
2003-5-30

4、獲取數據庫中字段名為”publish_time“、類型為Datetime的值
<%@ page import="java.util.Date"%>
<%
...連接數據庫...
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));
%>

輸出的結果為：
It is 星期五 2003.05.30 at 11:30:46 上午 CST
(更為詳盡的格式符號請參看SimpleDateFormat類)

6、將字符串轉換為日期
<%@ 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);
}
%>
輸出結果為：
Fri Nov 11 00:00:00 CST 1222

7、計算日期之間的間隔
<%@ 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.");
%>
輸出結果為：
Difference is 29 days.

8、日期的加減運算
方法：用Calendar類的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()));
%>
輸出結果為：
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、比較日期
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);
%>
輸出結果為：
Sat Jan 01 00:00:00 CST 2000 is after Fri Dec 31 00:00:00 CST 1999

10、記錄一件事所花費的時間
方法：調用兩次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.");
%>

輸出結果為：
Cyc starts at 1054275312432
Cyc ends at 1054275312442
This run took 10ms.

其它：如何格式化小數

<%@ page import="java.text.*"%>
<%
DecimalFormat df = new DecimalFormat(",###.00");
double aNumber = 33665448856.6568975;
String result = df.format(aNumber);
out.println(result);
%>

輸出結果為：
33,665,448,856.66

======================

日期比較：

在JAVA中日期的計算與比較可以使用Date和DateFormat來解決，下面是一段示例代碼：

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("現在時間:"+now);

　　　System.out.println("現在時間是否在16:00之前:"+date.before(df.parse("2004-12-24 16:00:00")));
　　}
　　catch(ParseException e){System.out.print(e.getMessage());
　　}
　}
}