Private Brain Key Generation and Public Address Not Matching Java
As bitaddress.org BrainWallet says in its display

Private Key (Wallet Import Format): 
5KV1o7tRK8pNqrPNYyi38nrik9r2Y85sjdgFDttnDiT1uZrQ1fj 


Wallet Import Format is the usual base58 armoring applied to the privatekey value with 'version' 0x80.
See https://en.bitcoin.it/wiki/Wallet_import_format or in more detail https://en.bitcoin.it/wiki/Base58Check_encoding . 
This is basically a duplicate of Is there a way to generate a brain wallet from the command line or console? although that uses bash+dc rather than Java.

Not tested, but it looks to me like VersionChecksummedBytes(0x80,bytes).toBase58() does this.