简化Java日期操作的开源项目DATE4J，超级好用

以往要使用Java对时间日期进行操作，可能会用到以下的一些类：
Date and its subclasses :
java.util.Date
java.sql.Date
java.sql.Timestamp
The calendar and time zone classes :
java.util.Calendar
java.util.GregorianCalendar
java.util.TimeZone
java.util.SimpleTimeZone
(for use with the Gregorian calendar only)
The formatting and parsing classes :
java.text.DateFormat
java.text.SimpleDateFormat
java.text.DateFormatSymbols
以上这么多类用起来是不是很麻烦呢，现在好了，有了DATE4J，就不用这么麻烦了。
下面是一些简单的实例：
//Examples
//Here are some quick examples of using date4j's DateTime class :
DateTime dateAndTime = new DateTime("2010-01-19 23:59:59");
DateTime dateAndTime = new DateTime("2010-01-19 23:59:59.123456789");
DateTime dateOnly = new DateTime("2010-01-19");
DateTime timeOnly = new DateTime("23:59:59");
DateTime dateOnly = DateTime.forDateOnly(2010,01,19);
DateTime timeOnly = DateTime.forTimeOnly(23,59,59,0);
DateTime dt = new DateTime("2010-01-15 13:59:15");
boolean leap = dt.isLeapYear(); //false
dt.getNumDaysInMonth(); //31
dt.getStartOfMonth(); //2010-01-01, 00:00:00.000000000
dt.getEndOfDay(); //2010-01-15, 23:59:59.999999999
dt.format("YYYY-MM-DD"); //formats as '2010-01-15'
dt.plusDays(30); //30 days after Jan 15
dt.numDaysfrom(someDate); //returns an int
dueDate.lt(someDate); //less-than
dueDate.lteq(someDate); //less-than-or-equal-to
//Although DateTime carries no TimeZone information internally, there are methods that take a TimeZone as a parameter :
DateTime now = DateTime.now(someTimeZone);
DateTime today = DateTime.today(someTimeZone);
DateTime fromMilliseconds = DateTime.forInstant(31313121L, someTimeZone);
birthday.isInFuture(someTimeZone);
dt.changeTimeZone(fromOneTimeZone, toAnotherTimeZone);
获取DATE4J.jar请访问DATE4J项目网站：http://www.date4j.net