序列化/反序列化自定义Map< Key，Object>在杰克逊 [英] Serialize/Deserialize custom Map<Key, Object> in Jackson

问题描述

我有一个非常简单的Map，想要在Jackson中进行序列化和反序列化，但是我无法使它正常工作。

I have a pretty simple Map I want to serialize and deserialize in Jackson, but I can't get it to work.

我尝试了以下操作：

@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);
    }

}

但我有一个例外

com.fasterxml.jackson.databind.JsonMappingException：无法从START_ARRAY令牌中反序列化java.util.LinkedHashMap实例

推荐答案

您需要在TurnKey中定义/覆盖fromString（）方法。 Jackson将使用toString（）进行序列化，并使用fromString（）进行反序列化。这就是错误消息中的找不到（Map）密钥反序列化器的含义：com.fasterxml.jackson.databind.JsonMappingException：找不到类型[简单的（Map）密钥反序列化器。类型，在com.fasterxml.jackson.databind.deser.DeserializerCache._handleUnknownKeyDeserializer（DeserializerCache.java:584）中的类编号。asgari.civilization.server.model.TurnKey] 。

You need to define/override the fromString() method in TurnKey. Jackson will use toString() to serialize and fromString() to deserialize. That's what "Can not find a (Map) Key deserializer" means in the error message Caused by: com.fasterxml.jackson.databind.JsonMappingException: Can not find a (Map) Key deserializer for type [simple type, class no.asgari.civilization.server.model.TurnKey] at com.fasterxml.jackson.databind.deser.DeserializerCache._handleUnknownKeyDeserializer(DeserializerCache.java:584).

不需要自定义KeyDeserializer。

A custom KeyDeserializer is not needed.

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