How to convert HashMap to json Array in android?

Question

I want to convert HashMap to json array my code is as follow:

Map<String, String> map = new HashMap<String, String>();

map.put("first", "First Value");

map.put("second", "Second Value");

I have tried this but it didn't work. Any solution?

JSONArray mJSONArray = new JSONArray(Arrays.asList(map));

Answer 1

Try this,

public JSONObject (Map copyFrom) 

Creates a new JSONObject by copying all name/value mappings from the given map.

Parameters copyFrom a map whose keys are of type String and whose values are of supported types.

Throws NullPointerException if any of the map's keys are null.

Basic usage:

JSONObject obj=new JSONObject(yourmap);

get the json array from the JSONObject

Edit:

JSONArray array=new JSONArray(obj.toString());

Edit:(If found Exception then You can change as mention in comment by @krb686)

JSONArray array=new JSONArray("["+obj.toString()+"]");

Answer 2

Since androiad API Lvl 19, you can simply do new JSONObject(new HashMap()). But on older API lvls you get ugly result(simple apply toString to each non-primitive value).

I collected methods from JSONObject and JSONArray for simplify and beautifully result. You can use my solution class:

package you.package.name;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.lang.reflect.Array;
import java.util.Collection;
import java.util.Map;

public class JsonUtils
{
    public static JSONObject mapToJson(Map<?, ?> data)
    {
        JSONObject object = new JSONObject();

        for (Map.Entry<?, ?> entry : data.entrySet())
        {
            /*
             * Deviate from the original by checking that keys are non-null and
             * of the proper type. (We still defer validating the values).
             */
            String key = (String) entry.getKey();
            if (key == null)
            {
                throw new NullPointerException("key == null");
            }
            try
            {
                object.put(key, wrap(entry.getValue()));
            }
            catch (JSONException e)
            {
                e.printStackTrace();
            }
        }

        return object;
    }

    public static JSONArray collectionToJson(Collection data)
    {
        JSONArray jsonArray = new JSONArray();
        if (data != null)
        {
            for (Object aData : data)
            {
                jsonArray.put(wrap(aData));
            }
        }
        return jsonArray;
    }

    public static JSONArray arrayToJson(Object data) throws JSONException
    {
        if (!data.getClass().isArray())
        {
            throw new JSONException("Not a primitive data: " + data.getClass());
        }
        final int length = Array.getLength(data);
        JSONArray jsonArray = new JSONArray();
        for (int i = 0; i < length; ++i)
        {
            jsonArray.put(wrap(Array.get(data, i)));
        }

        return jsonArray;
    }

    private static Object wrap(Object o)
    {
        if (o == null)
        {
            return null;
        }
        if (o instanceof JSONArray || o instanceof JSONObject)
        {
            return o;
        }
        try
        {
            if (o instanceof Collection)
            {
                return collectionToJson((Collection) o);
            }
            else if (o.getClass().isArray())
            {
                return arrayToJson(o);
            }
            if (o instanceof Map)
            {
                return mapToJson((Map) o);
            }
            if (o instanceof Boolean ||
                    o instanceof Byte ||
                    o instanceof Character ||
                    o instanceof Double ||
                    o instanceof Float ||
                    o instanceof Integer ||
                    o instanceof Long ||
                    o instanceof Short ||
                    o instanceof String)
            {
                return o;
            }
            if (o.getClass().getPackage().getName().startsWith("java."))
            {
                return o.toString();
            }
        }
        catch (Exception ignored)
        {
        }
        return null;
    }
}

Then if you apply mapToJson() method to your Map, you can get result like this:

{
  "int": 1,
  "Integer": 2,
  "String": "a",
  "int[]": [1,2,3],
  "Integer[]": [4, 5, 6],
  "String[]": ["a","b","c"],
  "Collection": [1,2,"a"],
  "Map": {
    "b": "B",
    "c": "C",
    "a": "A"
  }
}

Answer 3

A map consists of key / value pairs, i.e. two objects for each entry, whereas a list only has a single object for each entry. What you can do is to extract all Map.Entry<K,V> and then put them in the array:

Set<Map.Entry<String, String> entries = map.entrySet();
JSONArray mJSONArray = new JSONArray(entries);

Alternatively, sometimes it is useful to extract the keys or the values to a collection:

Set<String> keys = map.keySet();
JSONArray mJSONArray = new JSONArray(keys);

or

List<String> values = map.values();
JSONArray mJSONArray = new JSONArray(values);

Note: If you choose to use the keys as entries, the order is not guaranteed (the keySet() method returns a Set). That is because the Map interface does not specify any order (unless the Map happens to be a SortedMap).

Answer 4

This is the Simplest Method.

Just use

JSONArray jarray = new JSONArray(hashmapobject.toString);

Answer 5

You can use

JSONArray jarray = JSONArray.fromObject(map );