TimeZone.setDefault for a thread in Java 8

Don't use the system defaulting at all. Use ThreadLocal<T>: either a ThreadLocal<TimeZone>, or better, a ThreadLocal<ZoneId> with the java.time classes. Then you can fetch from there everywhere that you need the default.

Personally I'd try to avoid using a thread local at all, and pass around the context explicitly - or if you do want to have context implicitly, encapsulate all the context (e.g. for a web request) in an appropriate context type, rather than having separate thread locals for time zone, locale etc.