Key exported from BitcoinJ is different from the key shown by bitcoind
Sorry I have found the solution. The dumped privkey is not comparable to the address. If I want to use the dumped format, I have to use the class DumpedPrivateKey. 

Thanks for the help!

After  Aussie Cryptocurrency's request, I am pointing out the problem in the code.
What I was doing was trying to import the private key of the 'from' keypair using bitcoin-cli. However, it is important to know that such operations must be run using DumpedPrivateKey: this class can manage private keys in the format that bitcoin-cli likes, whereas in my previous tests I was trying to import the private key simply Base-58 encoding the private key. The odd thing is that if you do so, the key seems to be imported, but the private key is completely different to the expected one.

Hope this helps.