Thanks, there exists actually a similar library that Smack uses for XML construction in its unit tests, but I decided against my normal behavior and not re-use existing code for various reasons:
1. Since Smack targets Android and JVM you never know if a jar will actually run on all platforms and it's usually not easy to change 3rd party code to make it compatible again.
2. Smack follows the philosophy of being minimalistic, e.g. to not depend on to many 3rd party libraries
3. XmlStringBuilder provides some convenience methods for typical XMPP XML cases (e.g. optIntAttribute).
4. It uses LazyStringBuilder (but can be changed to strict)
5. It's a simple one file library, no real need to relay on other (bigger) libraries