How to solve Date Issues in Java

Java already provides powerful functions in dealing with Date (also Time) problems.
So you can input a String (i.e. “2001.07.04 AD at 12:08:56 PDT”), and get the Date Object by Java Methods.
In contrast, you can also provide a Date Object (or long number, etc.), and print the date as required date format easily.

What you need to done is just define the format String, i.e. “yyyy-mm-dd HH:mm:ss”. 
(Pay attention to the capticals, because they mean different format).
Here is a simple demostration.

Reference Codeimport java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;

import junit.framework.TestCase;

public class DateFormatTest extends TestCase {
 private final static String date1 = "2011-10-10 22:12:34";
 private final static long dateLong1 = Long.parseLong("1318252354000");
 private static DateFormat formatter1 = new SimpleDateFormat(
   "yyyy-MM-dd HH:mm:ss");

 private final static String date2 = "AM 12:34:56 04/09/85 JST";
 private final static long dateLong2 = Long.parseLong("481822496000");
 private static DateFormat formatter2 = new SimpleDateFormat(
   "aa hh:mm:ss MM/dd/yy zzz", Locale.ENGLISH);

 
 public void test1() throws ParseException {
  long dateLong = formatter1.parse(date1).getTime();
  System.out.println(this.getName() + ":  Long Number is " + dateLong);
  assertEquals(dateLong1, dateLong);
 }

 public void test2() throws ParseException {
  String dateString = formatter1.format(new Date(dateLong1));
  System.out.println(this.getName() + ":  Formatted Date String is "
    + dateString);
  assertEquals(date1, dateString);
 }

 public void test3() throws ParseException {
  long dateLong = formatter2.parse(date2).getTime();
  System.out.println(this.getName() + ":  Long Number is " + dateLong);
  assertEquals(dateLong2, dateLong);
 }

 public void test4() throws ParseException {
  String dateString = formatter2.format(new Date(dateLong2));
  System.out.println(this.getName() + ":  Formatted Date String is "
    + dateString);
  assertEquals(date2, dateString);
 }
}

The Output Result is :

test1:  Long Number is 1318252354000
test2:  Formatted Date String is 2011-10-10 22:12:34
test3:  Long Number is 481822496000
test4:  Formatted Date String is AM 12:34:56 04/09/85 JST

From Javadoc of JDK, we can easily learn how to write the format String.
Be careful on how to control the length of the items: i.e. the “yy” means here display the year, and two digits will be displayed.
Also, the “/” or “-” (or others) which are not defined in the table, will mean the separator.