Sort JSON objects by key in Java

I'm sorting JSON objects in a JSON array by passing the JSON key.

My program is working only when the json value is String

Example:- {"id":"0001"}

so whenever there is integer value program throws an error.

Example:- {"id":0001}

program:-

import java.util.*;
import org.json.*;
public class sample2 {
public static void main(String[] args) {
String jsonArrStr = "[ "
+ ""
+ "{ \"ID\": \"135\", \"Name\": \"Fargo Chan\" },"
+ "{ \"ID\": \"432\", \"Name\": \"Aaron Luke\" },"
+ "{ \"ID\": \"252\", \"Name\": \"Dilip Singh\" }]";
JSONArray jsonArr = new JSONArray(jsonArrStr);
JSONArray sortedJsonArray = new JSONArray();
List<JSONObject> jsonValues = new ArrayList<JSONObject>();
for (int i = 0; i < jsonArr.length(); i++) {
jsonValues.add(jsonArr.getJSONObject(i));
}
Collections.sort(jsonValues, new Comparator<JSONObject>() {
// You can change "Name" with "ID" if you want to sort by ID
private static final String KEY_NAME = "Name";
@Override
public int compare(JSONObject a, JSONObject b) {
System.out.println("a " + a.toString());
System.out.println("b " + b.toString());
String valA = new String();
String valB = new String();
try {
valA = (String) a.get(KEY_NAME);
System.out.println("valA " + valA);
valB = (String) b.get(KEY_NAME);
System.out.println("valB " + valB);
} catch (JSONException e) {
// do something
}
return valA.compareTo(valB);
// if you want to change the sort order, simply use the following:
// return -valA.compareTo(valB);
}
});
for (int i = 0; i < jsonArr.length(); i++) {
sortedJsonArray.put(jsonValues.get(i));
}
System.out.println(sortedJsonArray.toString());
}
}

How to make above program work dynamically for all the DATA-TYPES(String,Integer,Float,Double).

There are not many ways to to what you want to achieve. Refelection API is there but it comes with many drawbacks and not very reliable and straightforward. However, the most reliable and easy way is to use instanceof operator.

With this method you have full control over every conversion and comparison, also you can compare custom classes with compareTo() method implemented. Unless you have too many possibilities to cover, this maybe the best approach.

I assume that you know that JSONObject.get() method converts object into Object types so add conditions like

Object obj1 = a.get(KEY_NAME);
Object obj2 = b.get(KEY_NAME);
if(obj1 instanceof Integer && obj2 instanceof Integer){
return  ((Integer) obj1).compareTo(((Integer) obj2));
} else if(obj1 instanceof Double && obj2 instanceof Double){
return  ((Double) obj1).compareTo(((Double) obj2));
} else if(obj1 instanceof Double || obj2 instanceof Double){
Double v1 = ((Number) obj1).doubleValue();
Double v2 = ((Number) obj2).doubleValue();
return  v1.compareTo(v2);
}

> As Number class is super class of Integer, Float and Double, so you
> can convert it from there.

It may induce lot of code but will add reliability but no surprises when unexpexcted JSON is encountered. Also additional conditions would be able handle to handle mismatching data types and and could also detect error in JSON object.