FULL PRODUCT VERSION :
java version "1.6.0_03"
Java(TM) SE Runtime Environment (build 1.6.0_03-b05)
Java HotSpot(TM) Client VM (build 1.6.0_03-b05, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [Version 5.1.2600]

A DESCRIPTION OF THE PROBLEM :
Formatting a Date value, using SimpleDateFormat with the pattern "yyyy-MM-dd'T'HH:mm:ss.SSSZ" results in an output string with an RFC822-style time zone offset. For example: 2007-11-21T11:35:31.576-0700

Using the same SimpleDateFormat instance to parse this string is slow. It appears that the implementation is attempting to match a timezone identifier string (e.g. GMT or MST) even though the format specifier is Z, not z. This results in a large performance penalty.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Please see test case below.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Expected no significant performance penalty for parsing the date string with the Z format specifier.
ACTUAL -
Current date: 2007-11-21T11:35:31.576-0700
Elapsed time (slow): 1.625
Elapsed time (fast): 0.094

These results show that using the Z specifier to parse the timezone offset is more than 15x (1500%) slower than parsing it without the Z specifier.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

/**
 * This class demonstrates a performance issue when using the Z format specifier to
 * parse an RFC822-style (+/-HHMM) timezone offset.
 *
 * @author Dan Rabe
 */
public class SDFPerformance
{
public static void main( String[] args ) throws ParseException
{
long start;
long finish;
final int N = 10000; // Number of iterations
SimpleDateFormat slow = new SimpleDateFormat( "yyyy-MM-dd'T'HH:mm:ss.SSSZ" );
SimpleDateFormat fast = new SimpleDateFormat( "yyyy-MM-dd'T'HH:mm:ss.SSS" );
Date now = new Date();

String s = slow.format( now );
System.out.println( "Current date: " + s );

// Time to parse using Z format

start = System.currentTimeMillis();
for ( int i = 0; i < N; i++ )
{
Date d = slow.parse( s );
}
finish = System.currentTimeMillis();
System.out.println( "Elapsed time (slow): " + (finish-start)/1000.0 );

// Time to parse without Z format

start = System.currentTimeMillis();
for ( int i = 0; i < N; i++ )
{
Date d = fast.parse( s );
}
finish = System.currentTimeMillis();
System.out.println( "Elapsed time (fast): " + (finish-start)/1000.0 );
}
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
One option is to parse the string with the Z format specifier. The result still appears to be correct.

Another option is to make some assumptions about what time zone the date is in.

Another option is to use a literal 'Z' at the end of the format specifier to indicate that this is a Zulu (GMT) time, as suggested by the ISO 8601 standard and allowed by the w3c date/time note(http://www.w3.org/TR/NOTE-datetime).