日期和时间操作的Java工具：DATE4J

我们知道，在处理时间的时候，往往需要用到 Java 里的如下类：

1、Date and its subclasses:

java.util.Date  java.sql.Date  java.sql.Timestamp

2、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)

3、The formatting and parsing classes:

java.text.DateFormat  java.text.SimpleDateFormat  java.text.DateFormatSymbols

这些处理起来是非常之烦的。如果用DATE4J处理就容易很多了。例子如下：

package hirondelle.date4j;    import java.util.Locale;  import java.util.TimeZone;    /** Examples of how to use date4j. */  public final class Examples {      /**      Run the examples, and output to the console.          <P>Example output when you run this class:     <PRE>     Current date-time in default time zone : 2011-10-24 08:05:59     Current date-time in Cairo : 2011-10-24 13:06:00 (Monday)     Age of someone born May 16, 1995 is : 16     The 3rd Friday of this month is : 2011-10-21     Number of days till Christmas : 62     90 days from today is : 2012-01-22     3 months and 5 days from today is : 2012-01-29     Numbers of hours difference between Paris and Perth : 6     The number of weeks since Sep 6, 2010 : 59     This many seconds till midnight : 57240     Output using an ISO format: 2011-10-24T08:06:00     The first day of this week is : 2011-10-23     The number of years the JDK date-time API has been suctorial : 15    </PRE>      */    public static void main(String... aArgs){      Examples examples = new Examples();      examples.currentDateTime();      examples.currentDateTimeInCairo();      examples.ageIfBornOnCertainDate();      examples.optionsExpiry();      examples.daysTillChristmas();      examples.whenIs90DaysFromToday();      examples.whenIs3Months5DaysFromToday();      examples.hoursDifferenceBetweenParisAndPerth();      examples.weeksSinceStart();      examples.timeTillMidnight();      examples.imitateISOFormat();      examples.firstDayOfThisWeek();      examples.jdkDatesSuctorial();    }        // PRIVATE        private static void log(Object aMsg){      System.out.println(String.valueOf(aMsg));    }        /** What is the current date-time in the JRE's default time zone? */    private void currentDateTime(){      DateTime now = DateTime.now(TimeZone.getDefault());      String result = now.format("YYYY-MM-DD hh:mm:ss");      log("Current date-time in default time zone : " + result);    }        /** What is the current date-time in Cairo (include weekday)? */    private void currentDateTimeInCairo(){      DateTime now = DateTime.now(TimeZone.getTimeZone("Africa/Cairo"));      String result = now.format("YYYY-MM-DD hh:mm:ss (WWWW)", Locale.getDefault());      log("Current date-time in Cairo : " + result);    }        /** What's the age of someone born May 16, 1995? */    private void ageIfBornOnCertainDate(){      DateTime today = DateTime.today(TimeZone.getDefault());      DateTime birthdate = DateTime.forDateOnly(1995, 5, 16);      int age = today.getYear() - birthdate.getYear();      if(today.getDayOfYear() < birthdate.getDayOfYear()){        age = age - 1;       }      log("Age of someone born May 16, 1995 is : " + age);    }        /** Stock options expire on the 3rd Friday of this month. What day of the month is that? */    private void optionsExpiry(){      DateTime today = DateTime.today(TimeZone.getDefault());      DateTime firstOfMonth = today.getStartOfMonth();      int result = 0;      if (firstOfMonth.getWeekDay() == 7){        result = 21;      }      else {         result = 21 - firstOfMonth.getWeekDay();      }      DateTime thirdFriday = DateTime.forDateOnly(firstOfMonth.getYear(), firstOfMonth.getMonth(), result);      log("The 3rd Friday of this month is : " + thirdFriday.format("YYYY-MM-DD"));    }        /** How many days till the next December 25? */    private void daysTillChristmas(){      DateTime today = DateTime.today(TimeZone.getDefault());      DateTime christmas = DateTime.forDateOnly(today.getYear(), 12, 25);      int result = 0;      if(today.isSameDayAs(christmas)){        // do nothing      }      else if (today.lt(christmas)){        result = today.numDaysFrom(christmas);      }      else if (today.gt(christmas)){        DateTime christmasNextYear = DateTime.forDateOnly(today.getYear() + 1, 12, 25);        result = today.numDaysFrom(christmasNextYear);      }      log("Number of days till Christmas : " + result);    }        /** What day is 90 days from today? */    private void whenIs90DaysFromToday(){      DateTime today = DateTime.today(TimeZone.getDefault());      log("90 days from today is : " + today.plusDays(90).format("YYYY-MM-DD"));    }      /** What day is 3 months and 5 days from today? */    private void whenIs3Months5DaysFromToday(){      DateTime today = DateTime.today(TimeZone.getDefault());      DateTime result = today.plus(0,3,5,0,0,0,0,DateTime.DayOverflow.FirstDay);      log("3 months and 5 days from today is : " + result.format("YYYY-MM-DD"));    }        /** Current number of hours difference between Paris, France and Perth, Australia. */    private void hoursDifferenceBetweenParisAndPerth(){      //this assumes the time diff is a whole number of hours; other styles are possible      DateTime paris = DateTime.now(TimeZone.getTimeZone("Europe/Paris"));      DateTime perth = DateTime.now(TimeZone.getTimeZone("Australia/Perth"));      int result = perth.getHour() - paris.getHour();      if( result < 0 ) {        result = result + 24;      }      log("Numbers of hours difference between Paris and Perth : " + result);    }        /** How many weeks is it since Sep 6, 2010? */    private void weeksSinceStart(){      DateTime today = DateTime.today(TimeZone.getDefault());      DateTime startOfProject = DateTime.forDateOnly(2010, 9, 6);      int result = today.getWeekIndex() - startOfProject.getWeekIndex();      log("The number of weeks since Sep 6, 2010 : " + result);    }        /** How much time till midnight? */    private void timeTillMidnight(){      DateTime now = DateTime.now(TimeZone.getDefault());      DateTime midnight = now.plusDays(1).getStartOfDay();      long result = now.numSecondsFrom(midnight);      log("This many seconds till midnight : " + result);    }        /** Format using ISO style. */    private void imitateISOFormat(){      DateTime now = DateTime.now(TimeZone.getDefault());      log("Output using an ISO format: " + now.format("YYYY-MM-DDThh:mm:ss"));    }      private void firstDayOfThisWeek(){      DateTime today = DateTime.today(TimeZone.getDefault());       DateTime firstDayThisWeek = today; //start value       int todaysWeekday = today.getWeekDay();      int SUNDAY = 1;      if(todaysWeekday > SUNDAY){        int numDaysFromSunday = todaysWeekday - SUNDAY;        firstDayThisWeek = today.minusDays(numDaysFromSunday);      }      log("The first day of this week is : " + firstDayThisWeek);    }        /** For how many years has the JDK date-time API been suctorial? */    private void jdkDatesSuctorial(){      DateTime today = DateTime.today(TimeZone.getDefault());      DateTime jdkFirstPublished = DateTime.forDateOnly(1996, 1, 23);      int result = today.getYear() - jdkFirstPublished.getYear();      log("The number of years the JDK date-time API has been suctorial : " + result);    }      }

更加详细的信息，请大家查看官方的文档： http://www.date4j.net/