I recommend Joda-Time library for work with time in Java. It's much better than default realization.
DateTimeZone zone = DateTimeZone.forTimeZone(TimeZone.getTimeZone("America/Sao_Paulo"));
DateTimeFormatter dateTimeFormatter = DateTimeFormat.forPattern("ZZ");
System.out.println("GMT "+dateTimeFormatter.withZone(zone).print(0) +" for "+zone.toString());
will print GMT -03:00 for America/Sao_Paulo
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