如何在 Java 中使用 Jackson 对 JSON 响应进行建模？

Question

I am try to model an Api response using Jackson. The id will be the same type in all but the body will be different types.

An example response would be:

{
    "responses": [
        {
            "id": "jobTitle",
            "body": {
                "jobTitle": "Software Engineer"
            }
        },
        {
            "id": "thumbnailPhoto",
            "body": "base 64 bit string"
        }
    ]
}

I have the following implementation. Is this the correct approach? If the type for body returns as a string, would the JobTitle be ignored/ null?

@JsonIgnoreProperties(ignoreUnknown = true)
public class Response
{
  @JsonProperty("id")
  private String id;

  @JsonProperty("body")
  private String photo;

  @JsonProperty("body")
  private JobTitle jobTitle;

  // getters and setters
}

Answer 1

I'm no expert in this area, but I would like to share my answer here.

I don't know why you design the JSON string as an array of responses for your original question. I would suggest a better design to be a single instance of "Response" object as below:

{
 "id":"response id",
 "jobTitle":"title",
 "img":"img b64 string"
}

Just leave the field null if not exists.

But if you insist on using the origin design, below code below coding can be achieved, but the JSON string need small changes to add "type" info Tutorial from Baeldung .

[ {
  "id" : "1",
  "body" : {
    "type" : "jobTitle",
    "jobTitle" : "job title"
  }
}, {
  "id" : "2",
  "body" : {
    "type" : "img",
    "data" : "xxxxx"
  }
} ]

Java coding as below:

    package org.example.test4;

import com.fasterxml.jackson.annotation.JsonSubTypes;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

import java.util.ArrayList;

public class TestApp {

    public static class Response<X extends Body> {
        private String id;
        private X body;

        public String getId() {
            return id;
        }

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

        public X getBody() {
            return body;
        }

        public void setBody(X body) {
            this.body = body;
        }
    }
    @JsonTypeInfo(
            use = JsonTypeInfo.Id.NAME,
            include = JsonTypeInfo.As.PROPERTY,
            property = "type"
    )
    @JsonSubTypes({
            @JsonSubTypes.Type(value = JobTitle.class, name = "jobTitle"),
            @JsonSubTypes.Type(value = IMG.class, name = "img")
    })
    public static abstract class Body{}
    public static class JobTitle extends Body{
        private String jobTitle;

        public String getJobTitle() {
            return jobTitle;
        }

        public void setJobTitle(String jobTitle) {
            this.jobTitle = jobTitle;
        }
    }
    public static class IMG extends Body{
        private String data;

        public String getData() {
            return data;
        }

        public void setData(String data) {
            this.data = data;
        }
    }

    public static void main(String[] args) throws JsonProcessingException {
        ObjectMapper om = new ObjectMapper().enable(SerializationFeature.INDENT_OUTPUT);;
        JobTitle jt = new JobTitle();
        jt.setJobTitle("job title");
        System.out.println(om.writeValueAsString(jt));
        IMG img = new IMG();
        img.setData("xxxxx");
        System.out.println(om.writeValueAsString(img));
        ArrayList<Response<?>> rs = new ArrayList<Response<?>>();
        Response<JobTitle> r1 = new Response<JobTitle>();
        r1.setId("1");
        r1.setBody(jt);
        rs.add(r1);
        Response<IMG> r2 = new Response<IMG>();
        r2.setId("2");
        r2.setBody(img);
        rs.add(r2);
        System.out.println(om.writeValueAsString(rs));
    }
}