@Override
    public String deserialize(String topic, byte[] data) {
        if (data == null)
            return null;
        else
            return new String(data, encoding);
    }
String encoding defaults to UTF8 and can be customized by setting the property key.deserializer.encoding,
value.deserializer.encoding or deserializer.encoding. The first two take precedence over the last.
clients/src/main/java/org/apache/kafka/common/serialization/StringDeserializer.java