我使用kafka mqtt连接器从一个kafka主题的mqtt代理接收消息。然后我使用spark上的kafka消费者阅读了kafka主题中的这些信息。当我打印消息时，这就是结果。我怎样才能正确地阅读这些信息？
这是set consumer和create stream的代码。

SparkConf sparkConf = new SparkConf().setAppName("GestoreSoccorso").setMaster("local[2]");
JavaStreamingContext ssc = new JavaStreamingContext(sparkConf, new Duration(500));

Map<String, Object> kafkaParams = new HashMap<>();
kafkaParams.put("bootstrap.servers", "10.0.4.215:9092");
kafkaParams.put("key.deserializer", StringDeserializer.class);
kafkaParams.put("value.deserializer", StringDeserializer.class);
kafkaParams.put("group.id", "use_a_separate_group_id_for_each_stream");
kafkaParams.put("auto.offset.reset", "earliest");
kafkaParams.put("enable.auto.commit", false);
Collection<String> topics = Arrays.asList("ankioverdrive_v1_events");

JavaInputDStream<ConsumerRecord<String, String>> stream =
        KafkaUtils.createDirectStream(
                ssc,
                LocationStrategies.PreferConsistent(),
                ConsumerStrategies.<String, String>Subscribe(topics, kafkaParams)
        );

然后这是我用来读取主题中的消息并打印它们的代码。

stream.foreachRDD(new VoidFunction<JavaRDD<ConsumerRecord<String, String>>>() {
            @Override
            public void call(JavaRDD<ConsumerRecord<String, String>> consumerRecordJavaRDD) throws Exception {
                consumerRecordJavaRDD.foreach(new VoidFunction<ConsumerRecord<String, String>>() {
                    @Override
                    public void call(ConsumerRecord<String, String> stringStringConsumerRecord) throws Exception {
                        String stringa=stringStringConsumerRecord.value();
                        System.out.println(DEBUG+"DATI RICEVUTI -> "+ stringa);

最后是输出

DEBUG: DATI RICEVUTI ->     ܑ�՛Y
SKULL   �    unknown0%