Object class level custom deserializer not utilized when Object is Map key

[mluckam]

When an Object utilizes a class level custom deserialier @JsonDeserialize(using = XXX.class) or class level custom serializer @JsonSerialize(using = XXX.class), these are not utilized when deserializing/serializing the key of a map.

Example project linked shows use case with the class com.google.cloud.tools.jib.api.DescriptorDigest. Class level deserializer is utilized for class DescriptorDigest when deserialized directly or as a Set<DescriptorDigest>. The class level deserializer is not utilized when DescriptorDigest is a key or value in a map. Instead the constructor is called via MapDeserializer and StdKeyDeserializer.StringCtorKeyDeserializer. Note the same is true for serialization.

Is this the expected behavior? Collections are able to infer the type and utilize class level custom deserializers/serializers, so I found it odd that Map was unable to do this without an explicit @JsonDeserialize(keyUsing = <KeyDeserializer>.class), see code.

[cowtowncoder]

Key serializer/deserializer settings are not same as value (de)serializer: there are separate keyUsing methods because JSON Object keys are always Strings (and are exposed during different JsonToken).
This is different from Collections (JSON Arrays) where elements/contents can be of any legal value type.

So this distinction exists due to limitations on legal value types. In hindsight it might have been good idea to require JsonSerializer / JsonDeserializer expose methods for from/to-String (de)serialization, so one could register just one set of handlers.
But as things are, Key serializer/deserializer are distinct from regular ("value") (de)serializer.

So, in short: yes, this is expected: registering value serializer/deserializer does not register handler for Map key serialization/deserialization. Separate handlers are needed.