请问 Flink CDC 用API 读取kafka 的json记录，下面脚本报序列化报错，是序列?

请问 Flink CDC 用API 读取kafka 的json记录，下面脚本报序列化报错，是序列化写法不对吗

    JsonDeserializationSchema<RuleDetail> jsonFormat=new JsonDeserializationSchema<>(RuleDetail.class);

    KafkaSource<RuleDetail> source = KafkaSource.<RuleDetail>builder()
            .setBootstrapServers(brokers)
            .setTopics("kafka_src")
            .setGroupId("my-group")
            .setStartingOffsets(OffsetsInitializer.earliest())
            .setValueOnlyDeserializer(jsonFormat)
            .build();

    DataStreamSource<RuleDetail> kafkastream = env.fromSource(source, WatermarkStrategy.noWatermarks(), "Kafka Source");
    kafkastream.print();
    env.execute();？