how to remove json object from json Array using org.json.simple

Question

I have a JSON file which is an JSON ARRAY with some JSON Objects and I want to remove the entire json Object if the value of longitude or latitude is an empty string "".

I am using the library org.json.simple. Here is my json file:

  [ {       "Longitude": 9.96233,
            "Latitude": 49.80404 },
    
    {
            "Longitude": 6.11499,
            "Latitude": 50.76891
        
    },
     {      "Longitude": 6.80592,
            "Latitude": 51.53548
    },
     {
            "Longitude": 9.50523,
            "Latitude": 51.31991   },
     {
            "Longitude": ""
            "Latitude": ""
       
    },
     {
            "Longitude": 9.93368,
            "Latitude": ""
       
    },
    {
            "Longitude": 11.56122,
            "Latitude": 48.14496
      
    },

     {
            "Longitude": 13.34253,
            "Latitude": 52.5319
        
    },
     {
            "Longitude": 6.11327,
            "Latitude": 50.77715
      
    },
     {
            "Longitude": ""
            "Latitude": ""
        }
     ]

and here's where I am stuck. :

JSONParser jsonParser = new  JSONParser();
try (FileReader reader = new FileReader ("output.json")) {
    Object obj = jsonParser.parse(reader);
    JSONArray list = (JSONArray) obj;
    list.forEach(node -> {
        String vari = (String)((JSONObject)node).get("longitude").toString();            
        if (vari==null) {
            ((JSONObject) node).remove();
            System.out.println("deleted");          
        }
    }
    ...

Any suggestions how can I change my code ?

Answer 1

You need to remove the node from the list but because of concurrent modification problem (modifying the list you are looping) you need another list.

I think it is easiest to collect into the new list all the nodes that qualify so like:

@SuppressWarnings("unchecked")
@Test
public void test() throws Exception {
    JSONParser jsonParser = new JSONParser();
    JSONArray listNonNull = new JSONArray();
    try (FileReader reader = new FileReader("output.json")) {
        JSONArray list = (JSONArray) jsonParser.parse(reader);
        ((Collection<JSONObject>)list).forEach(node -> {
            // here any check that qualifies the node like also checking "Latitude"
            // Also no need to cast to a String
            Object vari = node.get("Longitude");
            if (vari != null && !vari.equals("")) {
                listNonNull.add(node);
            }
        });
    } catch (Exception e) {
        throw e;
    }
}

If you wish to use only the original list you can collect items to be removed to an another list and use it to remove nodes from the original list:

public void test2() throws Exception {
    JSONParser jsonParser = new JSONParser();
    JSONArray toBeRemoved = new JSONArray();
    try (FileReader reader = new FileReader("output.json")) {
        JSONArray list = (JSONArray) jsonParser.parse(reader);
        ((Collection<JSONObject>) list).forEach(node -> {
            Object vari = node.get("Longitude");
            // here any check that qualifies the node like also checking "Latitude"
            if (vari != null && !vari.equals("")) {
                return; // not to be removed
            }
            toBeRemoved.add(node);
        });
        list.removeAll(toBeRemoved);
    } catch (Exception e) {
        throw e;
    }
}