嵌套对象的简单 Jackson 反序列化

Question

这应该是微不足道的，但由于某种原因，我似乎无法做到正确。

我有以下 JSON 响应

{
  "info": "processing",
  "data": {
    "id": "123",
    "cars": [
      {
        "id": "1"
      },
      {
        "id": "2"
      }
    ]
  }
}

我试过用简单的 POJO 转换它

@JsonRootName(value = "data")
public class Product {

    String id;

    List<Car> cars;

}

和

public class Car {

    String id;

}

但这会返回一个Productid 和 products 为 null的空对象。当然我不需要JsonDeserialize为这个简单的动作编写自定义？

Answer 1

您必须创建 POJO，然后使用 Jackson ObjectMapper API 将 JSON 字符串读取为 java 对象。

这是基于您的示例字符串的工作代码。

@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({ "info", "data" })
public class Process {

    @JsonProperty("info")
    private String info;
    @JsonProperty("data")
    private Data data;
    @JsonIgnore
    private Map<String, Object> additionalProperties = new HashMap<String, Object>();

    @JsonProperty("info")
    public String getInfo() {
        return info;
    }

    @JsonProperty("info")
    public void setInfo(String info) {
        this.info = info;
    }

    @JsonProperty("data")
    public Data getData() {
        return data;
    }

    @JsonProperty("data")
    public void setData(Data data) {
        this.data = data;
    }

    @JsonAnyGetter
    public Map<String, Object> getAdditionalProperties() {
        return this.additionalProperties;
    }

    @JsonAnySetter
    public void setAdditionalProperty(String name, Object value) {
        this.additionalProperties.put(name, value);
    }

}

@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({ "id", "cars" })
public class Data {

    @JsonProperty("id")
    private String id;
    @JsonProperty("cars")
    private List<Car> cars = null;
    @JsonIgnore
    private Map<String, Object> additionalProperties = new HashMap<String, Object>();

    @JsonProperty("id")
    public String getId() {
        return id;
    }

    @JsonProperty("id")
    public void setId(String id) {
        this.id = id;
    }

    @JsonProperty("cars")
    public List<Car> getCars() {
        return cars;
    }

    @JsonProperty("cars")
    public void setCars(List<Car> cars) {
        this.cars = cars;
    }

    @JsonAnyGetter
    public Map<String, Object> getAdditionalProperties() {
        return this.additionalProperties;
    }

    @JsonAnySetter
    public void setAdditionalProperty(String name, Object value) {
        this.additionalProperties.put(name, value);
    }

}


@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({ "id" })
public class Car {

    @JsonProperty("id")
    private String id;
    @JsonIgnore
    private Map<String, Object> additionalProperties = new HashMap<String, Object>();

    @JsonProperty("id")
    public String getId() {
        return id;
    }

    @JsonProperty("id")
    public void setId(String id) {
        this.id = id;
    }

    @JsonAnyGetter
    public Map<String, Object> getAdditionalProperties() {
        return this.additionalProperties;
    }

    @JsonAnySetter
    public void setAdditionalProperty(String name, Object value) {
        this.additionalProperties.put(name, value);
    }

}

用于反序列化 JSON 字符串的代码。

import java.io.IOException;
import java.util.List;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class MainApp {

    public static void main(String[] args) throws JsonParseException, JsonMappingException, IOException {

        String input = "{\r\n" + 
                "  \"info\": \"processing\",\r\n" + 
                "  \"data\": {\r\n" + 
                "    \"id\": \"123\",\r\n" + 
                "    \"cars\": [\r\n" + 
                "      {\r\n" + 
                "        \"id\": \"1\"\r\n" + 
                "      },\r\n" + 
                "      {\r\n" + 
                "        \"id\": \"2\"\r\n" + 
                "      }\r\n" + 
                "    ]\r\n" + 
                "  }\r\n" + 
                "}";
        ObjectMapper mapper = new ObjectMapper();
        Process process = mapper.readValue(input, Process.class);
        System.out.println(process.getInfo());
        Data data = process.getData();
        List<Car> cars = data.getCars();
        for(Car car : cars) {
            System.out.println(car.getId());
        }

    }

}

希望这可以帮助。