java - jsonvalue - objectmapper jackson

Serializar/Deserializar mapa personalizado<Key, Object> en Jackson

Question

Tengo un mapa bastante simple que quiero serializar y deserializar en Jackson, pero no puedo hacerlo funcionar.

He probado lo siguiente:

@JsonSerialize(keyUsing=TurnKeySerializer.class)
@JsonDeserialize(keyUsing = TurnKeyDeserializer.class)
Map<TurnKey, PlayerTurn> publicTurns = new TreeMap<>();

@JsonIgnoreProperties(ignoreUnknown = true)
@Data //Creates Getter/Setter etc
public class TurnKey implements Comparable<TurnKey> {
    private final int turnNumber;
    private final String username;

    public TurnKey(int turnNumber, String username) {
        this.turnNumber = turnNumber;
        this.username = username;
    }

    @Override
    public int compareTo(TurnKey o) {
        int v = Integer.valueOf(turnNumber).compareTo(o.getTurnNumber());
        if (v != 0) {
            return v;
        }
        return username.compareTo(o.getUsername());
    }

    @Override
    public String toString() {
        return "{" +
                "turnNumber:" + turnNumber +
                ", username:''" + username + "''" +
                "}";
    }


public class TurnKeySerializer extends JsonSerializer<TurnKey> {
    @Override
    public void serialize(TurnKey value, JsonGenerator gen, SerializerProvider serializers) throws IOException, JsonProcessingException {
        if (null == value) {
            throw new IOException("Could not serialize object to json, input object to serialize is null");
        }
        StringWriter writer = new StringWriter();
        ObjectMapper mapper = new ObjectMapper();
        mapper.writeValue(writer, value);
        gen.writeFieldName(writer.toString());
    }
}


public class TurnKeyDeserializer extends KeyDeserializer {
    private static final ObjectMapper mapper = new ObjectMapper();

    @Override
    public TurnKey deserializeKey(String key, DeserializationContext ctxt) throws IOException, JsonProcessingException {
        return mapper.readValue(key, TurnKey.class);
    }

}

Pero recibo una excepción

com.fasterxml.jackson.databind.JsonMappingException: no se puede deserializar la instancia de java.util.LinkedHashMap con el token START_ARRAY