日期问题
1、获取服务器端当前日期：
<!--page import="java.util.Date--> <!--r> Date myDate = new Date(); -->
输出结果：
引用
Fri Jan 05 21:39:40 CST 2007
2、获取当前年、月、日：
<!--page import="java.util.Date--> <!--r> Date myDate = new Date(); int thisYear = myDate.getYear() + 1900; int thisMonth = myDate.getMonth() + 1; int thisDate = myDate.getDate(); -->
输出结果：
引用
2007 1 5
3、按本地时区输出当前日期
<!--page import="java.util.Date--> <!--r> Date myDate = new Date(); out.println(myDate.toLocaleString()); -->
结果：2007-1-5 21:43:27
4、获取数据库中字段名为”publish_time“、类型为Datetime的值
<!--page import="java.util.Date-->
<!--r> ...连接数据库...
ResultSet rs = ...
Date sDate = rs.getDate("publish_time");
-->
5、按照指定格式打印日期
<!--page import="java.util.Date-->
<!--page import="java.text.DateFormat-->
<!--r> 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 2007.01.05 at 21:43:27 下午 CST
6、将字符串转换为日期
<!--page import="java.util.Date-->
<!--page import="java.text.DateFormat-->
<!--r> 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-->
<!--r> 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.*-->
<!--r> 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("
");
out.println("Two years ago was " + formatter.format(now.getTime()));
-->
9、比较日期
方法：用equals()、before()、after()方法
<!--page import="java.util.*-->
<!--page import="java.text.*-->
<!--r> 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.*-->
<!--r> 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("
");
out.println("Cyc ends at " + t1);
out.println("
");
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
输出结果为：
33,665,448,856.66
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