jsp中的日期问题及其它

日期问题
1、获取服务器端当前日期
Date myDate = new Date();

2、获取当前年、月、日：
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
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
Date sDate = rs.getDate("publish_time");

5、按照指定格式打印日期
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
 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
 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
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
 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
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
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