如何在 Spring Boot 中反序列化 Kafka 主题中的 Json 字符串

Question

I created a POJO to map a payload received from a Kafka topic. It works if the format of payload is:

{"payload":{"name":notification,"key":"2637","message":"This is a notif"}

When I produce this message of JSON string type.

"{\"payload\":{\"name\":\"notification\",\"key\":\"2637\",\"message\":\"This is a notif\"}"

It is throwing

Could not read JSON:Cannot construct instance of myfilename : no sting-argument constructor/factory method to deserialize from string value.

How to fix it?

Answer 1

I think you just need to use a StringDeserializer if the message is just a String representing escaped JSON, and handle the message as a String. I don't think you can automatically bind to a POJO because it is not an actual JSON object.

You could write a custom deserializer to convert the String then delegate to an ObjectMapper.

Answer 2

Your issue possibly could be resolved by using below setting in the mapper :

mapper.enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);

On the side note, if you are already using spring-kafka , you can use the default JsonDesrializer or a custom deserializer.

consumerProps.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, JsonDeserializer.class);

More documentations are available in the spring documentation

Another ref : Deserialize kafka messages in KafkaConsumer using springboot