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

在網上經常看到有人問如何將 獲得當前時間并轉換成
yyyy-MM-dd 年-月-日
hh:mm:ss 小時-分鐘-秒
yyyy-MM-dd HH:mm:ss 年-月-日 小時-分鐘-秒
三種格式 下面就是 jsp GUI 的使用方法

<!--
jsp獲得當前日期
-->
<!-- 導入處理時間類,此類內部都是靜態方法,直接調用即可. -->
<%@ page import="com.Mamak.util.TimeString" %>
<%
//獲得當前日期時間
String nowDate = TimeString.getNowTime("yyyy-MM-dd");
String nowTime = TimeString.getNowTime("HH:mm:ss");
String nowDateTime = TimeString.getNowTime("yyyy-MM-dd HH:mm:ss");
out.println("nowDate: "+nowDate);
out.println("nowTime: "+nowTime);
out.println("nowDateTime: "+nowDateTime);
%>
//******************************************************
//GUI 或java 小程序獲得得當前日期
public class Test()
{
public static void main(String abc[])
{
//直接包名點類名點方法名使用
System.out.println("nowDate: "+com.Mamak.util.TimeString.getNowTime("yyyy-MM-dd"));
System.out.println("nowTime: "+com.Mamak.util.TimeString.getNowTime("HH:mm:ss"));
System.out.println("nowDateTime: "+com.Mamak.util.TimeString.getNowTime("yyyy-MM-dd HH:mm:ss"));
}
}
//******************************************************
//獲得時間的bean 文件名 TimeString.java
package com.Mamak.util;

import java.text.SimpleDateFormat;
import java.util.Calendar;

public class TimeString
{

public TimeString()
{
}

public static String getNowTime(String timeFormat)
{
SimpleDateFormat lformat = new SimpleDateFormat(timeFormat);
Calendar now = Calendar.getInstance();
String nowstr = lformat.format(now.getTime());
return nowstr;
}

public static String getNotTime()
{
return getNowTime("yyyy-MM-dd");
}
}