Java: AES encryption example

Encryption:

byte[] encrypt(byte[] plainText, String keySeed, byte[] iv) {
    if (plainText == null || iv == null)
        return null;

    try {
        SecretKey key = getSecretKey(keySeed);

        IvParameterSpec ivParm = new IvParameterSpec(iv);

        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");
        cipher.init(Cipher.ENCRYPT_MODE, key, ivParm);
        byte[] cipherText = cipher.doFinal(plainText);
        return cipherText;
    } catch (NoSuchAlgorithmException ex) {
    } catch (NoSuchPaddingException ex) {
    } catch (InvalidKeyException ex) {
    } catch (BadPaddingException ex) {
    } catch (IllegalBlockSizeException ex) {
    } catch (InvalidAlgorithmParameterException ex) {
    }

    return null;
}

Decryption:

byte[] decrypt(byte[] cipherText, String keySeed, byte[] iv) {
    if (cipherText == null || iv == null)
        return null;
    
    try {
        SecretKey key = getSecretKey(keySeed);

        IvParameterSpec ivParm = new IvParameterSpec(iv);

        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");
        cipher.init(Cipher.DECRYPT_MODE, key, ivParm);
        byte[] plaintext = cipher.doFinal(cipherText);
        return plaintext;
    } catch (NoSuchAlgorithmException ex) {
    } catch (NoSuchPaddingException ex) {
    } catch (InvalidKeyException ex) {
    } catch (BadPaddingException ex) {
    } catch (IllegalBlockSizeException ex) {
    } catch (InvalidAlgorithmParameterException ex) {
    }

    return null;
}

Helper methods:

byte[] generateIv() {
    SecureRandom random = new SecureRandom();
    byte bytes[] = new byte[16];
    random.nextBytes(bytes);

    return bytes;
}

SecretKey getSecretKey(String keySeed) throws NoSuchAlgorithmException {
    byte[] keySeedBytes = keySeed.getBytes();

    MessageDigest md = MessageDigest.getInstance("SHA-256");
    md.update(keySeedBytes);
    byte[] dgBytes = md.digest();   // generate a 32 bytes key

    SecretKey key = new SecretKeySpec(dgBytes, 0, dgBytes.length, "AES");
    return key;
}

Test code:

void test() {
    byte[] b = new byte[] { 1, 2, 3, 10, 20, 30, 100};
    String key = "mykey";

    byte[] iv = generateIv();

    byte[] enb = encrypt(b, key, iv);
    byte[] deb = decrypt(enb, key, iv);

    System.out.println(Arrays.equals(b, deb));
}

Output:
true