You might be interested in a Java implementation of BIP38, the passphrase protected private key format.
Credits to casascius for this very useful proposal.
Besides that this format is specially suited for physical Bitcoin storage, it is the primary key storage format in
bitsofproof implementation of the Bitcoin protocol. It enables the store of private keys in a database table individually
protected by potentially different passphrases.
https://github.com/bitsofproof/supernode/blob/master/api/src/main/java/com/bitsofproof/supernode/api/KeyFormatter.java