Convert string to appropriate date with timezone java

You need TWO format objects, one for parsing and another one for printing because you use two different timezones, see here:

// h instead of H  because of AM/PM-format
DateFormat parseFormat = new SimpleDateFormat("M/dd/yyyy hh:mm:ss aaa XXX"); 
Date dt = null;
try {
  dt = parseFormat.parse("3/15/2013 3:01:53 PM -06:00");
}catch (ParseException e) {
  e.printStackTrace();
} 

DateFormat printFormat = new SimpleDateFormat("M/dd/yyyy hh:mm:ss aaa XXX"); 
printFormat.setTimeZone(TimeZone.getTimeZone("GMT-05")); 
String newDateString = printFormat.format(dt);
System.out.println(newDateString);

Output: 3/15/2013 04:01:53 PM -05:00

If you want HH:mm:ss (24-hour-format) then you just replace

hh:mm:ss aaa 

by

HH:mm:ss

in printFormat-pattern.

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Comment on other aspects of question:

A java.util.Date has no internal timezone and always refers to UTC by spec. You cannot change it inside this object. A timezone conversion is possible for the formatted string, however as demonstrated in my code example (you wanted to convert to zone GMT-05).

The question then switches to the new requirement to print the Date-object in ISO-format using UTC timezone (symbol Z). This can be done in formatting by replacing the pattern with "yyyy-MM-dd'T'HH:mm:ssXXX" and explicitly setting the timezone of printFormat to GMT+00. You should clarify what you really want as formatted output.

About java.util.GregorianCalendar: Setting the timezone here is changing the calendar-object in a programmatical way, so it affects method calls like calendar.get(Calendar.HOUR_OF_DAY). This has nothing to do with formatting however!