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));

• user166390: So, you have a Map, but want an Array? Well, do that conversion first, independent of JSON, and then give the result (which is now a List/Array) to the appropriate JSON converter. The code posted won't work - and will result in a compiler error, which should be included in the post - because there is no Arrays.asList(Map<K,V>), as that doesn't make sense as there is no universal conversion (although, perhaps you want a List of the Entries?). That is, this question/problem has nothing to do with JSON directly.
• Sandeep: @pst: thanks but there is any solution on it? to create array with key=> value and convert it to json? in android activity
• user166390: Arrays don't have "key=>value". Provide sample Map data and the expected JSON Array output.
• subodh: Key value is only available with Map family in collection,try to convert Map into String and play with String.

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()+"]");

• Sandeep: I have tried but didn't work. Could you please paste code here?
• user166390: I have no idea by what logic that is supposed to work. I can only hope it's tested - showing input and what it produces (at each stage) would make this an acceptable answer.
• krb686: @Pragnani Unfortunately this doesn't work. Maybe it used to, but it doesn't anymore. This throws: A JSONArray text must start with '[' at character 1 At the line creating the JSONArray from the JSONObject Fix You need to change to: JSONArray array=new JSONArray("[" + obj.toString() + "]"); Could you edit that? Thanks
• Ed J: In java 7, api 26 android, none of the solutions above produce a valid json array output. The map.toString() function produces braces, {}, not brackets, []

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"
 }
}

• bstar55: Sweet! I wish I could give this +10! I'll have to look at the source code for API 19 to see if this is what they're doing. Thanks!
• Vans S: Had the same problem with undecodable string being sent looking like: {key=value, key2=value2}

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 );

• Asraful: try this : stackoverflow.com/questions/9210273/…
• Sadeshkumar Periyasamy: These classes are available in JSON-Lib library. You can find this library here: json-lib.sourceforge.net
• Sandeep: @Forhad: Thanks, But my hash created dynamically in my code so its not suitable for me is any other option to create array with key=>value and convert in json in android activity?