Your issue is that you need to encode/decode the ciphertext (just text in your code) if you want to transport it using a textual representation (String in your case).
Try and look up base 64 encoding on this site, there should be a lot of information about it. Encode after encryption and decode before decryption. You should also specify a specific character encoding for your plaintext.
Finally, you should probably encrypt with a symmetric cipher, and encrypt the symmetric key using RSA. Otherwise you may run out of space within the RSA calculation, because a public key cannot encrypt data larger than its modulus (key size).
