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Polymorphic JSON deserialization with Jackson #666
Description
I was wondering how to write a polymorphic parser for JSON CloudEvents, where the payload can be one of many types.
Normally, with plain Jackson one can do something like this, using @JsonTypeInfo and a type field somewhere in the JSON to determine the specific class for deserialization.
In this simple example in the CloudEvent SDK docs we knew the type in advance:
PojoCloudEventData<User> cloudEventData = mapData(
inputEvent,
PojoCloudEventDataMapper.from(objectMapper,User.class)
);But in my case, I would like to achieve something like the following:
@JsonTypeInfo(
use = JsonTypeInfo.Id.NAME,
property = "type"
)
@JsonSubTypes({
@JsonSubTypes.Type(value = Foo.class, name = "foo"),
@JsonSubTypes.Type(value = Bar.class, name = "bar")
})
sealed interface Payload permits Foo, Bar {}
record Foo(String str) implements Payload {}
record Bar(int i) implements Payload {}
// ...
PojoCloudEventData<Payload> cloudEventData = mapData(
inputEvent,
PojoCloudEventDataMapper.from(objectMapper, Payload.class)
);Running this code, it results in an error (as expected):
com.fasterxml.jackson.databind.exc.InvalidTypeIdException: Could not resolve subtype of [simple type, class Payload]: missing type id property 'type'
Because the type field is part of the CloudEvent header and/or envelope that Jackson does not know about at this point.
What's your take on this?
Activity
gustavomonarin commentedon Nov 1, 2024
@mbechto in previous versions, while using the structure mode with access to the object mapper, this could be achieved easily with a mixin by adding an external behavior to the cloudevents class.
I believe the same could be used somehow, but to be honest, i am having a hard time navigating PojoCloudEventData its Mapper and escipally CloudEvent complete excluding any generic type. Maybe could someone share the reasoning, i am sure there was.
For Mix in approach (pay attention on the JsonTypeInfo.As.EXTERNAL_PROPERTY):
the mixin interface:
So was just to register this interface to the CloudEvents interface, in this case we could do the same with the pojo, but i believe the sdk could help more here :(
I believe this could work if adjust your annotations to an interface targeting the
PojoCloudEventDatainstead of my CloudEvent focused.