java关于日期的运算等处理方法

http://www.blueidea.com/bbs/newsdetail.asp?id=989464

http://www.java-cn.com/bbs-jsp/show.jsp?id=133651&forum=base

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

<!–
jsp获得当前日期
–>
<!– 导入处理时间类,此类内部都是静态方法,直接调用即可. –>
<%@ 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”);
}
}