Create JSON object from List in Java

Question

I have a List<String> where each element represents a node and a String which is the value that corresponds to the last node of that list. The list represents the path to the value. So, basically each element of the list is the value of the previous element. I would like to create a JSON object from it using Jackson. However, this needs to be done dynamically, not explicitly setting the nodes of the JSON object, because the list will not always be the same.

So, I am wondering if there is a way to convert or iterate through the list and create the JSON object. So, if my list looks like this:

["user", "car", "brand"] and the value is "BMW", the JSON object should look like this:

{
   "user":
      {
        "car":
          {
            "brand": "BMW"
          }
      }
}

You could define a function that creates a JSON field in a given JSON Object, assigns a new JSON object to that field, and returns that new JSON object. Then you can iterate over your list, each time invoking the function with the value returned from the previous iteration. After iteration is done, assign the value. — Hulk
– Hulk, Commented Jul 16, 2020 at 14:07
Check this other answer stackoverflow.com/a/64621900/2403791 — TomasMolina
– TomasMolina, Commented Jun 1, 2022 at 5:59

dzimney · Accepted Answer · 2020-07-16 15:55:39Z

2

Iterate through the list in reverse and upon each iteration create a new JsonNode for the list element, add the previous JsonNode as a child to the new JsonNode and overwrite the original reference with the new JsonNode. Rinse and repeat.

Something like...

final String value = "BMW"; // whatever the final "value" is.
final ObjectMapper objectMapper = new ObjectMapper();

ObjectNode json = null;

for (int i = list.size() - 1; i >= 0; i--) {

  final String prop = list.get(i);
  final ObjectNode objectNode = objectMapper.createObjectNode();

  if (json == null) {
    objectNode.put(prop, value);
  } else {
    objectNode.put(prop, json);
  }

  json = objectNode;
}

edited Jul 16, 2020 at 15:55

answered Jul 16, 2020 at 14:20

dzimney

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Comments

Vishal Varshney · Accepted Answer · 2020-07-16 15:02:08Z

Here is the piece of code which you need

package uk.co.vishal;

import com.fasterxml.jackson.core.JsonProcessingException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Answer {

public static void main(String[] args) throws JsonProcessingException {
    List<String> data = new ArrayList<>();
    data.add("user");
    data.add("car");
    data.add("brand");

    System.out.println(data.toString());

    Map<String, String> mydata = new HashMap<>();
    Map<String, JSONObject> newdata = new HashMap<>();
    JSONObject result = new JSONObject();
    boolean flag = true;

    for (int i = data.size() - 1; i >= 0; i--) {
        if (flag) {
            mydata.put(data.get(i), "BMW");
            result = generateJson(mydata);
            flag = false;
        } else {
            newdata.put(data.get(i), result);
            result = generateJson(newdata);
            newdata.clear();
        }
    }
    System.out.println(result);
    /*
    * Here is the output:
    * {
        "user": {
            "car": {
                    "brand": "BMW"
                }
            }
      }
    *
    * */
}

private static JSONObject generateJson(Map data) {
    return new JSONObject(data);
}

}

I hope you will be sorted !!

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