傑克遜序列化和相關令牌（END_OBJECT），預計FIELD_NAME：缺少屬性'名稱'

Question

我想編寫使用傑克遜序列化/反序列化對象的代碼。

的對象在本質上是多態：

@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, "="); 
    } 

} 

我創建了一個Set<BaseQuery>用下面的代碼：

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，當我試圖序列我收到了以下JSON對象：

[ 
    { 
     "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文件時，我接收以下情況除外：

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) 

對於某些原因name字段是JSON根對象不存在。

如何解決？

修訂

它工作正常，當我試圖序列例如只megapixelCharacteristicQuery對象：

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，傑克遜形成以下JSON（用正確"name":"CompositeQuery"）：

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

但是當序列化/反序列化仍然不起作用時megapixelCharacteristicQuery位於HashSet<BaseQuery>之內。

如何使它與HashSet一起工作？

而且，甚至開始用HashSet做工精細當我添加defaultImpl = CompositeQuery.class到JsonTypeInfo註釋，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 { 
... 
} 

，但它是不是一種選擇我，因爲我不知道是什麼類型應在不同的情況下使用，所以我仍然在尋找解決方案如何在我的JSON中正確提供name參數。

Answer 1

最後，得益於以下問題Why does Jackson polymorphic serialization not work in lists?提供的答案我已經找到了解決辦法：

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

的伎倆。現在一切都按預期工作。