jXMPP is a XMPP base library that provides common functionality required by all kinds of XMPP implementations (servers, clients, components, …). One if its gems in
jxmpp-jid, which contains types for JIDs and comprehensive API for them. Remember the second commandment of XMPP development:
Ⅱ) Never shall thou use a String type to represents JIDs.
Check out the javadoc at http://jxmpp.org/releases/1.0.0/javadoc/
MiniDNS is a DNS library for Android and Java SE. Initially developed to bring native DNSSEC and DANE support to the Java ecosystem, including Android, it is now on the way to becoming a comprehensive DNS library, besides just a resolver library. Of course, it still can be used to perform DNS SRV resource records lookups, as it is common in XMPP. And for DANE verification (which we hope to become commonplace on day).
Check out the javadoc at http://minidns.org/releases/1.0.0/javadoc/