SimpleDateFormat.parse and SimpleDateFormat.format not producing identical values

We are using SimpleDateFormat in JAXB serialization/deserialization process of java.util.Date objects and I'm writing following utility to accomplish that 

public DateFormat getDateFormat(String format){ 
      DateFormat formatter = new SimpleDateFormat(format); 
      formatter.setLenient(false); 
      return formatter; 
} 

@Test  public void testMarshallUnmarshall(){ 
     String str1 = "2001-07-04T12:08:56.235-07:00"; // Example from http://docs.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html      DateFormat formatter = getDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSXXX"); 
     Date date = formatter.parse(str1); 
     String str2 = formatter.format(date); 
     assertEquals(str1.equals(str2)); //This fails }

What I noticed is str1 = "2001-07-04T12:08:56.235-07:00"; and str2 = 2001-07-04T14:08:56.235-05:00

What I need to do to make sure, both dates are same?

Thanks

Jon Skeet
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The two strings represent the same instant in time - it's just that one has a different UTC offset than the other.

That's to be expected - a Date only represents a point in time, and it looks like you've set up your SimpleDateFormat using the default system time zone. Therefore, any time you parse a value which has an offset other than the one that point in time would have in the system default time zone, you won't be able to round-trip the string.

If you compare the Date values, you'll find they are equal - in other words, if you compare formatter.parse(str2) with date, that should be fine.

Alternatively, use a format which is always in UTC, instead of one which specifies the time zone offset... or use a different data type which can preserve the offset.

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