How to get destination address from bitcoinj TransactionOutput?
TransactionOutput.getScriptPubKey.getToAddress.toString

Unfortunately, this gives an exception when dealing with an oldstyle pay-to-IP script, so you might have to deal with these yourself if you need them (which in your use case you probably won't). An example can be found in the Scala code from the link below (from line 120 on):

https://github.com/stefanwouldgo/Bitcoin-Graph-Explorer/blob/master/src/main/scala/Graph.scala