Java TimeZone Example

When you set a date-time value in java, you may encounter a timezone issue. You will find the date-time you get use java.util.Calendar class will always use the system default timezone. This example will tell you how to change it to show the date-time in your desired timezone.

1. java.util.TimeZone Properties And Methods.

1. TimeZone.getDefault() : This method will return a java.util.TimeZone object which represent current system used timezone.
2. TimeZone.getTimeZone(“Asia/Hong_Kong”) : This method will return a java.util.TimeZone object for a specified timezone id. You can click here to get all timezone id list.
3. getDisplayName() : Return the time zone display name.
4. getID() :  Return the timezone id. Such as “Pacific/Asia”.
5. getOffset( long currentTimeMillis ) : Return offset milliseconds between UTC and the used timezone.

2. Show Specified TimeZone Info Example.

1. The below java method will show the specified TimeZone info in the console.

   /* Show default or specified timezone info data. */
   public  void showSpecifiedTimeZoneInfo(String timeZoneId)
   {
       // Get current calendar.
       Calendar currCalendar = Calendar.getInstance();
   
       TimeZone targetTimeZone = null;
   
       if(timeZoneId==null || timeZoneId.trim().length()==0)
       {
           // Get default time zone.
           targetTimeZone = currCalendar.getTimeZone().getDefault();
       }else
       {
           // Get target time zone by id.
           targetTimeZone = TimeZone.getTimeZone(timeZoneId);
       }
   
       String targetTimeZoneDisplayName = targetTimeZone.getDisplayName();
       String targetTimeZoneId = targetTimeZone.getID();
       long targetTimeZoneOffSet = targetTimeZone.getOffset(System.currentTimeMillis());
       // Translate the milliseconds to hour.
       int offSetHour = (int)(targetTimeZoneOffSet / 1000 / 60 / 60);
   
       StringBuffer msgBuf = new StringBuffer();
       msgBuf.append("Time zone info. dislay name : ");
       msgBuf.append(targetTimeZoneDisplayName);
       msgBuf.append(" , id : ");
       msgBuf.append(targetTimeZoneId);
       msgBuf.append(" , offset hour : ");
       msgBuf.append(offSetHour);
   
       System.out.println(msgBuf.toString());
   }

3. Convert Date Time Between TimeZone Example.

1. The below java methods will convert date-time between different TimeZones.

   // Show a given date time milliseconds value in different timezone.
   private void convertBetweenTimeZone(long milliseconds, String srcTimeZoneId, String destTimeZoneId)
   {
       if(srcTimeZoneId!=null && srcTimeZoneId.trim().length() > 0 && destTimeZoneId!=null && destTimeZoneId.trim().length() > 0) {
   
           // Get the source and destination timezone object.
           TimeZone srcTimeZone = TimeZone.getTimeZone(srcTimeZoneId);
   
           TimeZone destTimeZone = TimeZone.getTimeZone(destTimeZoneId);
   
           // Get calendar object.
           Calendar calendar = Calendar.getInstance();
           calendar.setTimeInMillis(milliseconds);
   
           calendar.setTimeZone(srcTimeZone);
           String srcDateTime = this.getDateTime(calendar);
   
           calendar.setTimeZone(destTimeZone);
           String destDateTime = this.getDateTime(calendar);
   
           System.out.println("Date milliseconds : " + milliseconds);
           System.out.println("Source date time : " + srcDateTime);
           System.out.println("Destination date time : " + destDateTime);
       }
   }
   
   // Show a given date time in different time zone.
   private void convertBetweenTimeZone(int year, int month, int day, int hour, int minute, int second, String srcTimeZoneId, String destTimeZoneId)
   {
       if(srcTimeZoneId!=null && srcTimeZoneId.trim().length() > 0 && destTimeZoneId!=null && destTimeZoneId.trim().length() > 0) {
           Calendar calendar = Calendar.getInstance();
           calendar.set(Calendar.YEAR, year);
           calendar.set(Calendar.MONTH, month - 1);
           calendar.set(Calendar.DAY_OF_MONTH, day);
           calendar.set(Calendar.HOUR_OF_DAY, hour);
           calendar.set(Calendar.MINUTE, minute);
           calendar.set(Calendar.SECOND, second);
   
           this.convertBetweenTimeZone(calendar.getTimeInMillis(), srcTimeZoneId, destTimeZoneId);
       }
   }
   
   /* Get special calendar date time in string format. */
   private String getDateTime(Calendar calendar)
   {
       StringBuffer strBuffer = new StringBuffer();
       strBuffer.append("Date time : ");
       strBuffer.append(calendar.get(Calendar.YEAR));
       strBuffer.append("-");
       strBuffer.append(calendar.get(Calendar.MONTH) + 1);
       strBuffer.append("-");
       strBuffer.append(calendar.get(Calendar.DAY_OF_MONTH));
       strBuffer.append(" ");
       strBuffer.append(calendar.get(Calendar.HOUR_OF_DAY));
       strBuffer.append(":");
       strBuffer.append(calendar.get(Calendar.MINUTE));
       strBuffer.append(":");
       strBuffer.append(calendar.get(Calendar.SECOND));
       strBuffer.append(" Zone Id : ");
       strBuffer.append(calendar.getTimeZone().getID());
   
       strBuffer.append(", Zone Offset : ");
   
       long zoneOffSet = calendar.get(Calendar.ZONE_OFFSET);
       // Translate the milliseconds to hour.
       int offSetHour = (int)(zoneOffSet / 1000 / 60 / 60);
       strBuffer.append(offSetHour);
       strBuffer.append(" hour");
       return strBuffer.toString();
   }
   
   public static void main(String args[])
   {
       TimeZoneExample timeZoneExample = new TimeZoneExample();
       timeZoneExample.showSpecifiedTimeZoneInfo("America/Jamaica");
   
       timeZoneExample.convertBetweenTimeZone(System.currentTimeMillis(), "America/Los_Angeles", "Asia/Singapore");
   
       timeZoneExample.convertBetweenTimeZone(2000, 1, 1, 10, 26, 26, "America/Los_Angeles", "Asia/Singapore");
   
   }

2. Below is the example execution output.

   Date milliseconds : 1510222127526
   
   Source date time : Date time " 2021-11-9 2:8:47 Zone Id : America/Los_Angeles, Zone Offset : -8 hour
   
   Destination date time : Date time " 2021-11-9 18:8:47 Zone Id : Asia/Singapore, Zone Offset : 8 hour
   
   Date milliseconds : 946693586527
   
   Source date time : Date time " 2020-12-31 18:26:26 Zone Id : America/Los_Angeles, Zone Offset : -8 hour
   
   Destination date time : Date time " 2021-1-1 10:26:26 Zone Id : Asia/Singapore, Zone Offset : 8 hour