to load a KeyStore, you'll need to tell it the type of keystore it is (probably jceks), provide an inputstream, and a password. then, you can load it like so:
KeyStore ks = KeyStore.getInstance(TYPE_OF_KEYSTORE);
ks.load(new FileInputStream(PATH_TO_KEYSTORE), PASSWORD);
this can throw a KeyStoreException, so you can surround in a try block if you like, or re-throw. Keep in mind a keystore can contain multiple keys, so you'll need to look up your key with an alias, here's an example with a symmetric key:
SecretKeyEntry entry = (KeyStore.SecretKeyEntry)ks.getEntry(SOME_ALIAS,new KeyStore.PasswordProtection(SOME_PASSWORD));
SecretKey someKey = entry.getSecretKey();