JACKSON：如何在使用 Jackson 将 POJO 转换为 JSON 时忽略 POJO 名称？

Question

I am using Jackson 2.10.1 library to convert my Java POJOs to JSON and I am getting the below output, I require the output without the POJO name(MyTestPojo here), I have tried various jackson annotations like @JsonIgnoreProperties but those are mostly for POJO 中存在的成员而不是 POJO class 名称。

{
    "MyTestPojo": [
        {
            "CreatedBy": "user1",
            "Name": "testABC",
            "UpdatedBy": null,
            "UpdatedDate": null,
            "IsActive": true,
            "Value": "testABC1",
            "CreatedDate": "2017-03-13 15:41:54.0",
            "Description": "testABC"
        },
        {
            "CreatedBy": "user2",
            "Name": "testABC",
            "UpdatedBy": null,
            "UpdatedDate": null,
            "IsActive": false,
            "Value": "testABC2",
            "CreatedDate": "2017-03-13 15:41:54.0",
            "Description": "testABC"
        }
    ]
}

而我需要的是-

[
        {
            "CreatedBy": "user1",
            "Name": "testABC",
            "UpdatedBy": null,
            "UpdatedDate": null,
            "IsActive": true,
            "Value": "testABC1",
            "CreatedDate": "2019-03-13 15:41:54.0",
            "Description": "testABC"
        },
        {
            "CreatedBy": "user2",
            "Name": "testABC",
            "UpdatedBy": null,
            "UpdatedDate": null,
            "IsActive": false,
            "Value": "testABC2",
            "CreatedDate": "2020-03-10 15:41:54.0",
            "Description": "testABC"
        }
    ]
}

有没有办法用 Jackson 注释来处理这个问题？

我用过的 POJO 是——

@JacksonXmlRootElement(localName = "ArrayOfTestPojos")
public class GetResponseVO {

    @JsonProperty("MyTestPojo")
    @JacksonXmlProperty(localName = "MyTestPojo")
    @JacksonXmlElementWrapper(useWrapping = false)
    private ArrayList<MyTestPojo> MyTestPojoList;

    public ArrayList<MyTestPojo> getMyTestPojoList() {
        return MyTestPojoList;
    }

    public void setMyTestPojoList(ArrayList<MyTestPojo> MyTestPojoList) {
        this.MyTestPojoList = MyTestPojoList;
    }

// standard getters and setters

}

和

@JacksonXmlRootElement(localName = "MyTestPojo")
public class MyTestPojo {

    @JsonProperty("Name")
    private String name;

    @JsonProperty("Description")
    private String description;

    @JsonProperty("IsActive")
    private int isActive;

    @JsonProperty("Value")
    private String value = null;

    @JsonProperty("CreatedBy")
    private String createdBy;

    @JsonProperty("CreatedDate")
    private String createdDate;

    @JsonProperty("UpdatedBy")
    private String updatedBy;

    @JsonProperty("UpdatedDate")
    private String updatedDate;

// standard getters and setters.    
}
```````````
I am also generating the XML out of this so you can ignore the annotations relevant to XML.

Answer 1

您可以为此目的使用JsonValue注释，它基本上是“使用此属性的值而不是序列化容器对象”。 它也可以用于getters

@JsonValue 表示带注释的“getter”方法的结果（这意味着签名必须是 getter 的签名；非 void 返回类型，无参数）将用作实例序列化的单个值。 通常值是简单的标量类型（字符串或数字），但它可以是任何可序列化的类型（集合、Map 或 Bean）。

@JsonValue
@JacksonXmlProperty(localName = "MyTestPojo")
@JacksonXmlElementWrapper(useWrapping = false)
private ArrayList<MyTestPojo> MyTestPojoList;

但这是错误的做法，因为它会像这样生成 JSON ，这是不合法JSON 。

{[{"x":"value"}, ...]}

如果您只想更改 JSON 结构（不影响 xml），您可以为此目的使用MixIn 。

public interface JsonMixin {

   @JsonValue
   List<MyTestPojo> getMyTestPojoList();   
}

并将其注册到您的 object 映射器并从主 Class 中删除@JsonValue 。

objectMapper.addMixIn(GetResponseVO.class, JsonMixin.class);