How to check whether the given object is object or Array in JSON string

Question

I am getting JSON string from website. I have data which looks like this (JSON Array)

 myconf= {URL:[blah,blah]}

but some times this data can be (JSON object)

 myconf= {URL:{try}}

also it can be empty

 myconf= {}    

I want to do different operations when its object and different when its an array. Till now in my code I was trying to consider only arrays so I am getting following exception. But I am not able to check for objects or arrays.

I am getting following exception

    org.json.JSONException: JSONObject["URL"] is not a JSONArray.

Can anyone suggest how it can be fixed. Here I know that objects and arrays are the instances of the JSON object. But I couldn't find a function with which I can check whether the given instance is a array or object.

I have tried using this if condition but with no success

if ( myconf.length() == 0 ||myconf.has("URL")!=true||myconf.getJSONArray("URL").length()==0)

Stumper

Answer 1

JSON objects and arrays are instances of JSONObject and JSONArray, respectively. Add to that the fact that JSONObject has a get method that will return you an object you can check the type of yourself without worrying about ClassCastExceptions, and there ya go.

if (!json.isNull("URL"))
{
    // Note, not `getJSONArray` or any of that.
    // This will give us whatever's at "URL", regardless of its type.
    Object item = json.get("URL"); 

    // `instanceof` tells us whether the object can be cast to a specific type
    if (item instanceof JSONArray)
    {
        // it's an array
        JSONArray urlArray = (JSONArray) item;
        // do all kinds of JSONArray'ish things with urlArray
    }
    else
    {
        // if you know it's either an array or an object, then it's an object
        JSONObject urlObject = (JSONObject) item;
        // do objecty stuff with urlObject
    }
}
else
{
    // URL is null/undefined
    // oh noes
}

Emboly

Thanks. I have edited my question may be it will make more sense what I am wondering about. Can you give example for if (item instanceof JSONArray). What should I put in if condition? – Stumper

That is the example. The instanceof operator will tell you if item is a JSONArray. Hold on, lemme flesh it out a bit. – Emboly

Thanks Chao. Actually it worked. But the string can be empty also. So I am getting error for that also. if(!myconf.isNull("URL")||(myconf.getJSONArray("URL")!=null)||myconf.getJSONArray("URL").length()>0) {Object item = myconf.get("URL"); //other code} I am getting exception JSONObject["URL"] not found. – Stumper

@Judy: What do you mean by "the string can be empty"? – Emboly

Actually I have edited the question also. I mean the Json contains nothing i.e. myconf= { } Hence there will be no URL also in the string. – Stumper

K, first off, quit stuffing everything on one line. You're going to have to do different stuff based on whether it's null, or an array, or an object, right? Well, a boolean can only have two states, and you have three possible outcomes. Break things up a little. – Emboly

You're from the "Braces-At-New-Line" guild.... You shall not pass! – Fitton

@MagnoC: Haven't been for years. :) I just don't believe in editing posts to reflect such trivialities. – Emboly

Answer 2

Quite a few ways.

This one is less recommended if you are concerned with system resource issues / misuse of using Java exceptions to determine an array or object.

try{
 // codes to get JSON object
} catch (JSONException e){
 // codes to get JSON array
}

Or

This is recommended.

if (json instanceof Array) {
    // get JSON array
} else {
    // get JSON object
}

Luganda

Thanks, I know how to remove exceptions. I am concerned about checking the contents of the object and checking whether URL is array or an object. – Stumper

Yep, if you hit an exception trying to get an object when it is a JSON array, then you provide the implementation to get an array in the catch clause. This is one way though not recommended. – Luganda

Actually I am looking for a function which can be used in if condition for the check. – Stumper

Answer 3

I was also having the same problem. Though, I've fixed in an easy way.

My json was like below:

[{"id":5,"excerpt":"excerpt here"}, {"id":6,"excerpt":"another excerpt"}]

Sometimes, I got response like:

{"id":7, "excerpt":"excerpt here"}

I was also getting error like you. First I had to be sure if it's JSONObject or JSONArray.

JSON arrays are covered by [] and objects are with {}

So, I've added this code

if (response.startsWith("[")) {
  //JSON Array
} else {
  //JSON Object 
}

That worked for me and I wish it'll be also helpful for you because it's just an easy method

See more about String.startsWith here - https://www.w3schools.com/java/ref_string_startswith.asp

Inconspicuous

Answer 4

The below sample code using jackson api can be used to always get the json string as a java list. Works both with array json string and single object json string.

import com.fasterxml.jackson.databind.ObjectMapper;

public class JsonDataHandler {
    public List<MyBeanClass> createJsonObjectList(String jsonString) throws JsonMappingException, JsonProcessingException {
        ObjectMapper objMapper = new ObjectMapper();
        objMapper.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);
        List<MyBeanClass> jsonObjectList = objMapper.readValue(jsonString, new TypeReference<List<MyBeanClass>>(){});
        return jsonObjectList;
    }
}

Bowra

This should absolutely be the accepted answer now - using a built-in feature of Jackson is far better than try...catch...try or a bunch of if...else clauses. – Burtonburty

Answer 5

Using @Chao answer i can solve my problem. Other way also we can check this.

This is my Json response

{
  "message": "Club Details.",
  "data": {
    "main": [
      {
        "id": "47",
        "name": "Pizza",

      }
    ],

    "description": "description not found",
    "open_timings": "timings not found",
    "services": [
      {
        "id": "1",
        "name": "Free Parking",
        "icon": "http:\/\/hoppyclub.com\/uploads\/services\/ic_free_parking.png"
      } 
    ]
  }
}

Now you can check like this that which object is JSONObject or JSONArray in response.

String response = "above is my reponse";

    if (response != null && constant.isJSONValid(response))
    {
        JSONObject jsonObject = new JSONObject(response);

        JSONObject dataJson = jsonObject.getJSONObject("data");

        Object description = dataJson.get("description");

        if (description instanceof String)
        {
            Log.e(TAG, "Description is JSONObject...........");
        }
        else
        {
            Log.e(TAG, "Description is JSONArray...........");
        }
    }

This is used for check that received json is valid or not

public boolean isJSONValid(String test) {
        try {
            new JSONObject(test);
        } catch (JSONException ex) {
            // e.g. in case JSONArray is valid as well...
            try {
                new JSONArray(test);
            } catch (JSONException ex1) {
                return false;
            }
        }
        return true;
    }

Chelseachelsey