Unable to deserialize the response to java class object

Question

While parsing a json response to Java class object using ObjectMapper, I am getting parsing JsonMappingException with message - Can not deserialize instance of com.handson.ResponseParser out of START_ARRAY token

Assuming I have below json response -

{
    "statuses": [
      {
        "engine": "f4651cbc-a79c-4269-9711-1aeaaeff6369",
        "invocations": [
          {
            "outputs": {
              "aggrplan": {
                "path": "http://someurl.com",
                "repo": "S3",
                "format": "application/json"
              }
            },
            "message": "complete",
            "status": "200"
          }
        ]
      }
    ],
    "request_id": "fce46502095607ef"
}

In main method, I am doing parsing via below logic ->

ResponseParser parser = null;
        if(result.length() > 0) {
            ObjectMapper objectMapper = new ObjectMapper();
            objectMapper.configure(DeserializationConfig.Feature.UNWRAP_ROOT_VALUE, true);
            parser = objectMapper.readValue(result, ResponseParser.class);
        }

This is the class to which I want to map the json response:

@JsonRootName(value = "statuses")
public class ResponseParser {

    @JsonProperty(value = "request_id")
    private String requestId;


    @JsonProperty(value = "statuses")
    private List<Map<String, String>> statuses;

    public String getRequestId() {
        return requestId;
    }

    public void setRequestId(String requestId) {
        this.requestId = requestId;
    }

    public List<Map<String, String>> getStatuses() {
        return statuses;
    }

    public void setStatuses(List<Map<String, String>> statuses) {
        this.statuses = statuses;
    }
}

Answer 1

Your POJO does not fit to JSON payload. First of all, you do not need to DeserializationConfig.Feature.UNWRAP_ROOT_VALUE because ResponseParser is your root object. Secondly, instead of List<Map<String, String>> you need to use List<Map<String, Object>> - Map with Object values not with String values. See below example:

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.File;
import java.util.List;
import java.util.Map;

public class JsonApp {

    public static void main(String[] args) throws Exception {
        File jsonFile = new File("./resource/test.json").getAbsoluteFile();

        ObjectMapper mapper = new ObjectMapper();
        System.out.println(mapper.readValue(jsonFile, ResponseParser.class));
    }
}

class ResponseParser {

    @JsonProperty(value = "request_id")
    private String requestId;

    private List<Map<String, Object>> statuses;

    public String getRequestId() {
        return requestId;
    }

    public void setRequestId(String requestId) {
        this.requestId = requestId;
    }

    public List<Map<String, Object>> getStatuses() {
        return statuses;
    }

    public void setStatuses(List<Map<String, Object>> statuses) {
        this.statuses = statuses;
    }

    @Override
    public String toString() {
        return "ResponseParser{" +
                "requestId='" + requestId + '\'' +
                ", statuses=" + statuses +
                '}';
    }
}

Above code prints:

ResponseParser{requestId='fce46502095607ef', statuses=[{engine=f4651cbc-a79c-4269-9711-1aeaaeff6369, invocations=[{outputs={aggrplan={path=http://someurl.com, repo=S3, format=application/json}}, message=complete, status=200}]}]}