issue with parsing json string with List

Question

I have converted a DOM document to json String. However, there are some issues with the way List is mapped in scenario where the List has only one value and List has multiple values.

For ex: 1) After DOM document has been convered to json string, here AlphaStatus List has only with one value:

{
    "Gamma": {
          .
          .
          .
          .
          "AlphaStatuses": {
            "AlphaStatus": {
                    "AlphaHeaderKey": "201612221122273660",
                    "AlphaLineKey": "201612221122273661",
                 }
            },
        "Delta": {
            ...
        }
    }
}

2) After DOM document has been convered to json string, here AlphaStatus List has only with multiple values is shown as:

{
    "Gamma": {
          .
          .
          .
          .
          "AlphaStatuses": {
            "AlphaStatus": [
                {
                    "AlphaHeaderKey": "201612221122273660",
                    "AlphaLineKey": "201612221122273661",

                },
                {
                    "AlphaHeaderKey": "201612221122273660",
                    "AlphaLineKey": "201612221122273662",

                },
                {
                    "AlphaHeaderKey": "201612221122273660",
                    "AlphaLineKey": "2016}2221122273663",

                }
            ]
        },
        "Delta": {
            ...
        }
    }
}

I am using the below jackson code to convert xml string to json:

ObjectMapper mapper = new ObjectMapper();
mapper.enable(SerializationFeature.INDENT_OUTPUT);
Object json = mapper.readValue(jObject.toString(), Object.class);
String output = mapper.writeValueAsString(json);

My question is, how do i ensure that AlphaStatus List is always starting with [{ and ending with }], no matter whether it has only one value or multiple values. How can this be resolved. It is causing issues in the other system which assumes that AlphaStatus is a List always and expects [{ to be part of the token.

Any help is appreciated.? Or should i use some string utility in such cases to parse AlphaStatus and replace with [{ and }]. How can this be done

Answer 1

First, it seems the line

Object json = mapper.readValue(jObject.toString(), Object.class);

is useless, because you already have an object (jObject) to serialize.

Just use it:

String output = mapper.writeValueAsString(jObject);

For second, it seems your problematic field is of type java.lang.Object, right?

If you as assign a single value to it, it will result in one single Json object:

jObject.setAlphaStatuses(alphaStatus); -> result -> {...}

If you as assign some kind of collection, it will result in a Json array:

jObject.setAlphaStatuses(Arrays.asList(alphaStatus1, alphaStatus2)); -> result -> [{...},{...}]

To avoid that, either always pass a list or (if you can change the definition of the class) make it to a Collection (maybe some List).

Here a small snippet to test:

import java.util.Arrays;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class JsonObjects {

    private final static ObjectMapper mapper = new ObjectMapper();

    private final static AlphaStatus as1 = new AlphaStatus();
    private final static AlphaStatus as2 = new AlphaStatus();

    static {
        as1.setAlphaHeaderKey("A");
        as1.setAlphaLineKey("B");

        as2.setAlphaHeaderKey("C");
        as2.setAlphaLineKey("D");
    }

    public static void main(String[] args) throws JsonProcessingException {

        final Gamma gamma = new Gamma();

        gamma.setAlphaStatuses(Arrays.asList(as1, as2));

        System.out.println(mapper.writeValueAsString(gamma));

        gamma.setAlphaStatuses(as1);

        System.out.println(mapper.writeValueAsString(gamma));

    }

    static class Gamma {

        Object alphaStatuses;

        public Object getAlphaStatuses() {
            return alphaStatuses;
        }

        public void setAlphaStatuses(Object alphaStatuses) {
            this.alphaStatuses = alphaStatuses;
        }
    }

    static class AlphaStatus {

        String alphaHeaderKey;
        String alphaLineKey;

        public String getAlphaHeaderKey() {
            return alphaHeaderKey;
        }

        public void setAlphaHeaderKey(String alphaHeaderKey) {
            this.alphaHeaderKey = alphaHeaderKey;
        }

        public String getAlphaLineKey() {
            return alphaLineKey;
        }

        public void setAlphaLineKey(String alphaLineKey) {
            this.alphaLineKey = alphaLineKey;
        }
    }
}

And the result (not exactly your result, only for demonstration):

{"alphaStatuses":[{"alphaHeaderKey":"A","alphaLineKey":"B"},{"alphaHeaderKey":"C","alphaLineKey":"D"}]}
{"alphaStatuses":{"alphaHeaderKey":"A","alphaLineKey":"B"}}