http://anandsekar.github.io/exporting-the-private-key-from-a-jks-keystore/
public class ExportPrivateKey {
private File keystoreFile;
private String keyStoreType;
private char[] password;
private String alias;
private File exportedFile;
public static KeyPair getPrivateKey(KeyStore keystore, String alias, char[] password) {
try {
Key key=keystore.getKey(alias,password);
if(key instanceof PrivateKey) {
Certificate cert=keystore.getCertificate(alias);
PublicKey publicKey=cert.getPublicKey();
return new KeyPair(publicKey,(PrivateKey)key);
}
} catch (UnrecoverableKeyException e) {
} catch (NoSuchAlgorithmException e) {
} catch (KeyStoreException e) {
}
return null;
}
public void export() throws Exception{
KeyStore keystore=KeyStore.getInstance(keyStoreType);
BASE64Encoder encoder=new BASE64Encoder();
keystore.load(new FileInputStream(keystoreFile),password);
KeyPair keyPair=getPrivateKey(keystore,alias,password);
PrivateKey privateKey=keyPair.getPrivate();
String encoded=encoder.encode(privateKey.getEncoded());
FileWriter fw=new FileWriter(exportedFile);
fw.write(“—–BEGIN PRIVATE KEY—–\n“);
fw.write(encoded);
fw.write(“\n“);
fw.write(“—–END PRIVATE KEY—–”);
fw.close();
}
public static void main(String args[]) throws Exception{
ExportPrivateKey export=new ExportPrivateKey();
export.keystoreFile=new File(args[0]);
export.keyStoreType=args[1];
export.password=args[2].toCharArray();
export.alias=args[3];
export.exportedFile=new File(args[4]);
export.export();
}
}