How to support S/MIME using java.

Question

Hi all,

I want to send S/MIME encrypted mail but, while sending I am getting an error :

I tried sending an encrypted attachment through Java code but got an error when accessing it after downloading.

below is the code I am using :

KeyStore keystore = KeyStore.getInstance("PKCS12");
        FileInputStream fis = new FileInputStream("Path/keystore.p12");
        keystore.load(fis, "p12password".toCharArray());
        PrivateKey privateKey = (PrivateKey) keystore.getKey("myalias", "p12password".toCharArray());
        Certificate cert = keystore.getCertificate("myalias");
        Certificate recipientCert = keystore.getCertificate("myalias");

Questions:

1. How can I install the S/MIME extension?
2. The Java code I provided is right or wrong?
3. If not then what is the right to send and read S/MIME encrypted messages using Java code?