Spring stream binds to String instead to pojo - spring-cloud

Question

We just upgraded our Spring to:
Spring boot: 2.1.0.RELEASE
Spring cloud: Greenwich.SR1
Spring integration kafka: 3.1.0.RELEASE
Spring kafka: 2.2.7.RELEASE
and we're using
Kafka 2.1.1
We have a topic that more than one type of class instances can be sent to, all extend from the same abstract class. Let's the abstract class named AbstractMessage and there are to subclasses MessageImpl1 and MessageImpl2.
We used to receive it in the consumer as an object (in order to write a log if a mistaken class has been received somehow) and then cast it to the relevant MessageImpl by using if(message instanceof MessageImpl){}
After the upgrade, all the messages were bound to String instead to their classes.
I read here that content-type=application/json binds to a pojo, but even though I added in both input and output it was bound to a string:
spring.cloud.stream.bindings.input.contentType=application/json
spring.cloud.stream.bindings.output.contentType=application/json
Trying to receive the MessageImpl directly got this error:
Caused by: com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot
construct instance of MessageImpl1 (no Creators, like default
construct, exist): cannot deserialize from Object value (no delegate-
or property-based Creator)
at [Source: (byte[])
Any idea how to fix it?

Answer 1

What version did you upgrade from? Show your code and configuration properties. Previous versions used Kryo serialization by default, which is now deprecated in favor of JSON, but your POJOs need to be json-friendly.
The Kryo serialization is deprecated, but you can add the converter.
See the documentation.
Provided MessageConverters
As mentioned earlier, the framework already provides a stack of MessageConverters to handle most common use cases. The following list describes the provided MessageConverters, in order of precedence (the first MessageConverter that works is used):
ApplicationJsonMessageMarshallingConverter: Variation of the org.springframework.messaging.converter.MappingJackson2MessageConverter. Supports conversion of the payload of the Message to/from POJO for cases when contentType is application/json (DEFAULT).
TupleJsonMessageConverter: DEPRECATED Supports conversion of the payload of the Message to/from org.springframework.tuple.Tuple.
ByteArrayMessageConverter: Supports conversion of the payload of the Message from byte[] to byte[] for cases when contentType is application/octet-stream. It is essentially a pass through and exists primarily for backward compatibility.
ObjectStringMessageConverter: Supports conversion of any type to a String when contentType is text/plain. It invokes Object’s toString() method or, if the payload is byte[], a new String(byte[]).
JavaSerializationMessageConverter: DEPRECATED Supports conversion based on java serialization when contentType is application/x-java-serialized-object.
KryoMessageConverter: DEPRECATED Supports conversion based on Kryo serialization when contentType is application/x-java-object.
JsonUnmarshallingConverter: Similar to the ApplicationJsonMessageMarshallingConverter. It supports conversion of any type when contentType is application/x-java-object. It expects the actual type information to be embedded in the contentType as an attribute (for example, application/x-java-object;type=foo.bar.Cat).
When no appropriate converter is found, the framework throws an exception. When that happens, you should check your code and configuration and ensure you did not miss anything (that is, ensure that you provided a contentType by using a binding or a header). However, most likely, you found some uncommon case (such as a custom contentType perhaps) and the current stack of provided MessageConverters does not know how to convert. If that is the case, you can add custom MessageConverter. See User-defined Message Converters.