Can not find a (Map) Key deserializer for type [simple type, class …]

This was asked a long time ago, and is the first google result when looking up the error, but the accepted answer has no code and might be confusing for a jackson beginner (me). I eventually found this answer that helped.

So, as stated in accepted answer, Implementing and register a “key deserializer” is the way to go. You can do this like this.

SimpleModule simpleModule = new SimpleModule();
simpleModule.addKeyDeserializer(YourClass.class, new YourClassKeyDeserializer());
objectMapper.registerModule(simpleModule);

And for the class, all you have to do is:

class YourClassKeyDeserializer extends KeyDeserializer
{
    @Override
    public Object deserializeKey(final String key, final DeserializationContext ctxt ) throws IOException, JsonProcessingException
    {
        return null; // replace null with your logic
    }
}

That’s it! No annotation on classes, not custom deserializer for maps, etc.