java关于日期的运算等处理方法

jsp中的日期问题及其它:D :D :D

/**
* @author imagebear
*/

日期问题
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; 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

在网上经常看到有人问如何将获得当前时间并转换成
yyyy-MM-dd 年-月-日
hh:mm:ss 小时-分钟-秒
yyyy-MM-dd HH:mm:ss 年-月-日小时-分钟-秒
三种格式下面就是 jsp GUI 的使用方法



<%@ page import="com.Mamak.util.TimeString" %>
<%
//获得当前日期时间
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 小程序获得得当前日期
public class Test()
{
public static void main(String abc[])
{
//直接包名点类名点方法名使用
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"));
}
}
//******************************************************
//获得时间的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");
}
}

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