Improve Deserialization of InstanceEvents

[ChunMengLu]

Bug report
I customized eventstore and found that it is not good enough for deserialization.
I use jackson and need to customize a Deserializer like RegistrationDeserializer.

[joshiste]

Could you please elaborate a bit on your customizing and why you need to deserialize the InstanceEvents using jackson?
What changes to the InstanceEvents would you apply to improve it?

[ChunMengLu]

Because the memory currently used for InstanceEvents storage, spring boot admin will be lost after restart, so I use rocksdb to store. Use jackson for serialization.

[ChunMengLu]

Currently I use custom deserialization:

/**
 * InstanceEvent Deserializer
 *
 * @author L.cm
 */
public class InstanceEventDeserializer extends StdDeserializer<InstanceEvent> {

	public InstanceEventDeserializer() {
		super(InstanceEvent.class);
	}

	@Override
	public InstanceEvent deserialize(JsonParser jsonParser, DeserializationContext context) throws IOException {
		JsonNode node = jsonParser.readValueAsTree();
		String type = node.at("/type").asText();
		InstanceId instance = InstanceId.of(node.at("/instance").asText());
		long version = node.at("/version").asLong();
		Instant timestamp = Instant.parse(node.at("/timestamp").asText());

		if ("DEREGISTERED".equals(type)) {
			return new InstanceDeregisteredEvent(instance, version, timestamp);
		} else if ("ENDPOINTS_DETECTED".equals(type)) {
			List<Endpoint> endpoints = JsonUtil.convertValue(node.at("/endpoints"), JsonUtil.getListType(Endpoint.class));
			return new InstanceEndpointsDetectedEvent(instance, version, timestamp, Endpoints.of(endpoints));
		} else if ("INFO_CHANGED".equals(type)) {
			Map<String, Object> value = JsonUtil.convertValue(node.at("/info"), Map.class);
			return new InstanceInfoChangedEvent(instance, version, timestamp, Info.from(value));
		} else if ("REGISTERED".equals(type)) {
			Registration registration = JsonUtil.convertValue(node.at("/registration"), Registration.class);
			return new InstanceRegisteredEvent(instance, version, timestamp, registration);
		} else if ("REGISTRATION_UPDATED".equals(type)) {
			Registration registration = JsonUtil.convertValue(node.at("/registration"), Registration.class);
			return new InstanceRegistrationUpdatedEvent(instance, version, timestamp, registration);
		} else if ("STATUS_CHANGED".equals(type)) {
			Map<String, Object> value = JsonUtil.convertValue(node.at("/statusInfo"), Map.class);
			return new InstanceStatusChangedEvent(instance, version, timestamp, StatusInfo.from(value));
		}
		return null;
	}
}

[joshiste]

@ChunMengLu Currently I think the best is to provide a jackson module with your deserializer by SBA as I'm currently refusing to taint the code with the jackson polymorphic deserialization stuff.
Do you want to work on a PR for this?

[srempfer]

I started the development of #684 and as pre-requirement I need a Jackson module for the InstanceEvent stuff.
I'll contribute the module as separate PR for this issue because I not know how long the Redis based event store will take to implement.