Jackson序列化和nexpected令牌（END_对象），预期字段名称：缺少属性“NAME”

Question

我正在尝试编写使用Jackson对对象进行序列化/反序列化的代码。

这些对象本质上是多态的：

@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, "=");
    }

}

我已经创建了一个集

    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);

现在，当我尝试序列化对象时，我收到以下JSON：

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

但当我尝试反序列化JSON文档时，我收到了以下异常：

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)

出于某种原因，JSON根对象中缺少name字段。

怎么修？

更新

它工作正常，当我尝试序列化只有例如百万像素特征查询对象：

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

在本例中，Jackson形成以下JSON（使用正确的“名称”：“CompositeQuery”）：

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

但是序列化/反序列化仍然不起作用，当百万像素特性查询放在HashSet中时

如何使它与HashSet一起工作？

此外，当我添加defaultImpl=CompositeQuery时，即使使用HashSet，它也可以正常工作。类到JsonTypeInfo注释，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 {
...
}

但这对我来说不是一个选项，因为我不知道在不同的情况下应该使用什么类型，所以我仍然在寻找一个解决方案，如何在我的JSON中正确地提供name参数。




Answer 1

最后，感谢以下问题中提供的答案，为什么Jackson多态序列化在列表中不起作用？我找到了一个解决方案：

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

成功了。现在一切都按预期进行。