傑克遜序列化和預期令牌（END_OBJECT），預期FIELD_NAME：缺少屬性“名稱”

Question

我正在嘗試編寫使用Jackson序列化/反序列化對象的代碼。

這些對象本質上是多態的：

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "name")
@JsonSubTypes({
    @Type(value = ComparableQuery.class),
    @Type(value = CompositeQuery.class)
})
public abstract class BaseQuery {

    private final Long characteristicId;

...
}

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "name")
public class CompositeQuery extends BaseQuery {

    private final String operator;
    private final BaseQuery[] queries;

    public CompositeQuery(Long characteristicId, Operator operator, BaseQuery... queries) {
        super(characteristicId);
        this.operator = operator.value;
        this.queries = queries;
    }

...
}

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "name")
@JsonSubTypes({
    @Type(value = EqualQuery.class),
    @Type(value = GreaterOrEqualQuery.class),
    @Type(value = GreaterQuery.class),
    @Type(value = LessOrEqualQuery.class),
    @Type(value = LessQuery.class)
})
public abstract class ComparableQuery extends BaseQuery {

    private final Object value;

    private final String comparisonOperator;

...
}

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "name")
public class EqualQuery extends ComparableQuery {

    public EqualQuery(Long characteristicId, Object value) {
        super(characteristicId, value, "=");
    }

}

我用以下代碼創建了Set<BaseQuery> ：

    Set<BaseQuery> queries = new HashSet<>();

    BaseQuery megapixelCharacteristicQuery = new CompositeQuery(megapixelCharacteristic.getCharacteristicId(), CompositeQuery.Operator.AND, new GreaterOrEqualQuery(megapixelCharacteristic.getCharacteristicId(), 10), new LessOrEqualQuery(megapixelCharacteristic.getCharacteristicId(), 50));
    queries.add(megapixelCharacteristicQuery);

現在，當我嘗試序列化對象時，會收到以下JSON：

[
   {
      "characteristicId":391,
      "operator":"AND",
      "queries":[
         {
            "name":"GreaterOrEqualQuery",
            "characteristicId":391,
            "value":10,
            "comparisonOperator":">="
         },
         {
            "name":"LessOrEqualQuery",
            "characteristicId":391,
            "value":50,
            "comparisonOperator":"<="
         }
      ]
   }
]

但是當我嘗試反序列化JSON文檔時，我收到以下異常：

com.fasterxml.jackson.databind.JsonMappingException: Unexpected token (END_OBJECT), expected FIELD_NAME: missing property 'name' that is to contain type id  (for class com.example.decision.query.characteristic.BaseQuery)
 at [Source: [{"characteristicId":391,"operator":"AND","queries":[{"name":"GreaterOrEqualQuery","characteristicId":391,"value":10,"comparisonOperator":">="},{"name":"LessOrEqualQuery","characteristicId":391,"value":50,"comparisonOperator":"<="}]}]; line: 1, column: 233] (through reference chain: java.util.HashSet[0])
    at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:261)

由於某種原因，JSON根對象中沒有name字段。

如何解決？

更新

當我嘗試僅序列化例如megapixelCharacteristicQuery對象時，它工作正常：

BaseQuery megapixelCharacteristicQuery = new CompositeQuery(megapixelCharacteristic.getCharacteristicId(), CompositeQuery.Operator.AND, new GreaterOrEqualQuery(megapixelCharacteristic.getCharacteristicId(), 10), new LessOrEqualQuery(megapixelCharacteristic.getCharacteristicId(), 50));

在這種情況下，Jackson形成以下JSON（帶有正確的"name":"CompositeQuery" ）：

{
   "name":"CompositeQuery",
   "characteristicId":391,
   "operator":"AND",
   "queries":[
      {
         "name":"GreaterOrEqualQuery",
         "characteristicId":391,
         "value":10,
         "operator":">="
      },
      {
         "name":"LessOrEqualQuery",
         "characteristicId":391,
         "value":50,
         "operator":"<="
      }
   ]
}

但是將megapixelCharacteristicQuery放在HashSet<BaseQuery>內時，序列化/反序列化仍然不起作用。

如何使其與HashSet一起使用？

另外，當我向JsonTypeInfo批注中添加defaultImpl = CompositeQuery.class時，即使使用HashSet ，它也可以開始正常工作，例如：

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "name", defaultImpl = CompositeQuery.class)
@JsonSubTypes({
    @Type(value = ComparableQuery.class),
    @Type(value = CompositeQuery.class)
})
public abstract class BaseQuery {
...
}

但這不是我的選擇，因為我不知道在不同情況下應使用哪種類型，因此我仍在尋找一種解決方案，該方法如何在JSON中正確提供name參數。

Answer 1

最后，感謝以下問題中提供的答案， 為什么傑克遜多態序列化在列表中不起作用？ 我找到了解決方案：

Set<BaseQuery> queries = new HashSet<BaseQuery>() {
};

做到了。 現在一切都按預期進行。