Flattening multidimensional JSON in JAVA

Question

I have a JSON which looks like this,

{
 "users": [
 {
 "displayName": "Sharad Dutta",
 "givenName": "",
 "surname": "",
 "extension_user_type": "user",
 "identities": [
 {
 "signInType": "emailAddress",
 "issuerAssignedId": "[email protected]"
 }
 ],
 "extension_timezone": "VET",
 "extension_locale": "en-GB",
 "extension_tenant": "EG12345"
 }, 
 {
 "displayName": "Sharad Dutta",
 "givenName": "",
 "surname": "",
 "extension_user_type": "user",
 "identities": [
 {
 "signInType": "emailAddress",
 "issuerAssignedId": "[email protected]"
 }
 ],
 "extension_timezone": "VET",
 "extension_locale": "en-GB",
 "extension_tenant": "EG12345"
 }
 ]
}

I am writing a Java code where I am parsing this Multidimensional JSON to FLAT JSON. If you look closely, the JSON is wrapped in a "users" wrapper and then has couple of users as objects. For each user, there is a field called "identifiers" which is again a wrapper.

I want to flat this JSON, I have written a code but it is leaving a JSON blob for identifiers, for non nested it is working fine

JSONObject output;
 try {
 output = new JSONObject(userJsonAsString);
 JSONArray docs = output.getJSONArray("users");
 System.out.println(docs);

This is giving me below output, however i still have to flat inner wrapper "identifiers"

[
 {
 "extension_timezone": "VET",
 "extension_tenant": "EG12345",
 "extension_locale": "en-GB",
 "identities": [
 {
 "signInType": "emailAddress",
 "issuerAssignedId": "[email protected]"
 }
 ],
 "displayName": "Sharad Dutta",
 "surname": "",
 "givenName": "",
 "extension_user_type": "user"
 },
 {
 "extension_timezone": "VET",
 "extension_tenant": "EG12345",
 "extension_locale": "en-GB",
 "identities": [
 {
 "signInType": "userName",
 "issuerAssignedId": "pdhongade007"
 }
 ],
 "displayName": "Wayne Rooney",
 "surname": "Rooney",
 "givenName": "Wayne",
 "extension_user_type": "user"
 }
]

This is what I need,

{
 "extension_timezone": "VET",
 "extension_tenant": "EG12345",
 "extension_locale": "en-GB",
 "signInType": "emailAddress",
 "issuerAssignedId": "[email protected]",
 "displayName": "Sharad Dutta",
 "surname": "",
 "givenName": "",
 "extension_user_type": "user"
 }

I have to then parse this to CSV, which I know how, I just need to flat this further. Any help will be appreciated. I tried looking around, but a lot of them were using external dependencies.

//UPDATE

{
 "extension_timezone": "VET",
 "extension_tenant": "EG12345",
 "extension_locale": "en-GB",
 "signInType": "userName",
 "displayName": "Wayne Rooney",
 "surname": "Rooney",
 "givenName": "Wayne",
 "issuerAssignedId": "pdhongade007",
 "extension_user_type": "user"
}

When I tried @Jakub solution, I am getting the flat JSON, however it is not iterating for all the users. Just one!(I am guessing the last user only)

Answer 1

Please try the below approach, this will give you a comma separated format for both user and identifier (flat file per se),

 public static void main(String[] args) throws JSONException, ParseException {
 
 String userJsonFile = "path to your JSON";
 final StringBuilder sBuild = new StringBuilder();
 final StringBuilder sBuild2 = new StringBuilder();
 
 try {
 String userJsonAsString = convert your JSON to string and store in var;
 } catch (Exception e1) {
 e1.printStackTrace();
 }
 JSONParser jsonParser = new JSONParser();
 JSONObject output = (JSONObject) jsonParser.parse(userJsonAsString);
 try {
 
 JSONArray docs = (JSONArray) output.get("users");
 Iterator<Object> iterator = docs.iterator();
 
 
 while (iterator.hasNext()) {
 JSONObject userEleObj = (JSONObject)iterator.next();
 JSONArray nestedIdArray = (JSONArray) userEleObj.get("identities");
 Iterator<Object> nestIter = nestedIdArray.iterator();
 
 while (nestIter.hasNext()) {
 JSONObject identityEleObj = (JSONObject)nestIter.next(); 
 identityEleObj.keySet().stream().forEach(key -> sBuild2.append(identityEleObj.get(key) + ","));
 userEleObj.keySet().stream().forEach(key -> {
 if (StringUtils.equals((CharSequence) key, "identities")) {
 sBuild.append(sBuild2.toString());
 sBuild2.replace(0, sBuild2.length(), "");
 } else {
 sBuild.append(userEleObj.get(key) + ","); 
 }
 
 });
 
 }
 sBuild.replace(sBuild.lastIndexOf(","), sBuild.length(), "\n"); 
 }
 
 System.out.println(sBuild);
 
 } catch (Exception e) {
 e.printStackTrace();
 }
 }

• Sharad esdee Dutta: I tried you approach it worked! perfectly. thanks I am marking as answer

Answer 2

You can traverse the json and just store the "leafs" in map. Note: array of primitives will turn into the last value in the array with this approach, but that's what you described :)

Something like this:

void flatJson() throws JSONException {
 JSONObject object = new JSONObject(userJsonAsString); // this is your input
 Map<String, Object> flatKeyValue = new HashMap<>();
 readValues(object, flatKeyValue);
 System.out.println(new JSONObject(flatKeyValue)); // this is flat
}
void readValues(JSONObject object, Map<String, Object> json) throws JSONException {
 for (Iterator it = object.keys(); it.hasNext(); ) {
 String key = (String) it.next();
 Object next = object.get(key);
 readValue(json, key, next);
 }
}
void readValue(Map<String, Object> json, String key, Object next) throws JSONException {
 if (next instanceof JSONArray) {
 JSONArray array = (JSONArray) next;
 for (int i = 0; i < array.length(); ++i) {
 readValue(json, key, array.opt(i));
 }
 } else if (next instanceof JSONObject) {
 readValues((JSONObject) next, json);
 } else {
 json.put(key, next);
 }
}

• Sharad esdee Dutta: Do you have a link?
• Jakub: Not sure what link you are after ?
• Sharad esdee Dutta: I was trying to read you code, I am not sure about calling structure, and where I am feeding my JSON string in the code. I am trying to write a code which will follow a main() method type of structure. I am not sure how will I embed your code in mine.
• Jakub: I added comments to make it easier to follow, you can copy-paste the code and put content of flatJson into main method to run it.
• Sharad esdee Dutta: I tried your solution, it is giving me a flat JSON but its is not giving output for both users, just one user ( the last user it got) i think some problem with iterator.