Jackson：在对象的不同属性中反序列化JSON-Array [英] Jackson: Deserialize JSON-Array in different attributes of an object

问题描述

我需要解码以下JSON结构：

I need to decode the following JSON-Structure:

{
  "id":1
  "categories": [
    value_of_category1,
    value_of_category2,
    value_of_category3
  ]
}

我想要反序列化的对象属于以下类：

The object I am trying to deserialize into is of the following class:

class MyClass {
  public Integer id;
  public Category1 category1;
  public Category2 category2;
  public Category3 category3;
...
}

public enum Category1{
...
}

public enum Category2{
...
}

public enum Category3{
...
}

在JSON中，categories-Array的第一个条目始终是枚举Category1的值，第二个条目始终是枚举Category2的值，第三个条目始终是枚举类别3的值。

In the JSON the first entry of the categories-Array is always a value of the enum Category1, the second entry is always a value of the enum Category2 and the third entry is always a value of the enum Category3.

如何使用Jackson将此JSON反序列化为我的类结构？

How can I deserialize this JSON into my class structure using Jackson?

推荐答案

您可以通过扩展 JsonDeserializer< T> class。

You can create your custom deserializer by extending the JsonDeserializer<T> class.

以下是满足您需求的示例实现

Here is a sample implementation to fit your needs

public class MyClassDeserializer extends JsonDeserializer<MyClass>{

    @Override
    public MyClass deserialize(JsonParser jp, DeserializationContext ctxt)
            throws IOException, JsonProcessingException {
        JsonNode node = jp.getCodec().readTree(jp);
        int id = (Integer) ((IntNode) node.get("id")).numberValue();

        JsonNode categories = node.get("categories");
        Iterator<JsonNode> iter = categories.elements();

        while(iter.hasNext()){
            //create Category object based on an incrementing counter
        }

        MyClass myClass = //compose myClass from the values deserialized above.

        return myClass;
    }

}

要使用它，你只需拥有它使用 @JsonDeserialize 注释 MyClass ，指向您的自定义反序列化器。

To use it, you just have to annotate MyClass with @JsonDeserialize pointing to your custom deserializer.

@JsonDeserialize(using = MyClassDeserializer.class)
public class MyClass {

    private Integer id;
    private Category1 category1;
    private Category2 category2;
    private Category3 category3;

}

不相关，但作为一个好习惯，让你所有的字段private然后公开公共setter和getter以控制类的字段。

Not related, but as a good practice, make all your fields private then expose public setters and getters in order to control the fields of the class.

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