How to parse a JSON file and extract all the polylines in a list?

[Marin Capranov]

Hi!

I am trying to parse a JSON file that contains polylines and points. The thing is it returns only the first value of the first object and stops. Am I missing something in the loop? I need all the polylines so I can display them on the map. Cheers!

public void parseDirect(String response) {
       
        PolylineOptions polylineOptions = new PolylineOptions();
        List<LatLng> movements = new ArrayList<>();
        try{
            JSONObject json = new JSONObject(response);
            //Retrieve routes from response
            JSONObject jsonRoute = json.getJSONArray("routes").getJSONObject(0);
            //Retrieve legs from routes
            JSONObject legs = jsonRoute.getJSONArray("legs").getJSONObject(0);
            //Retrieve steps from legs
            JSONArray steps = legs.getJSONArray("steps");
            final int numSteps = steps.length();
            JSONObject step;
            //Retrieve points from steps
            for (int i = 0; i < numSteps; i++) {
                step = steps.getJSONObject(i);
                String pontos = step.getJSONObject("polyline").getString("points");
                movements.addAll(PolyUtil.decode(pontos));
            }

//            movementsTest.add(new LatLng(52.4634252,-1.8861262));
//            movementsTest.add(new LatLng(52.4761324,-1.8608113));
//            movementsTest.add(new LatLng(52.4634252,-1.8689613));

            polylineOptions.color(Color.RED);
            polylineOptions.width(10);
            polylineOptions.addAll(movements);

            mMap.clear();
            mMap.addPolyline(polylineOptions);
            Log.i("parser", "parseDirect: " + movements.toString());
        }catch(Exception ex){
            Log.d("DirectionErr",ex.getMessage());
        }

        //make use of movements object here
    }

 @Override
    protected void onPostExecute(String s) {

        parseDirect(s);

        Log.i("test", "onPostExecute: " + s);
    }

[Stephan van Hulst]

Please post example input, expected output, and actual output.

Like I said in your other topic, it's easier to process JSON using a binding API like Jackson or JSON-B. Parsing it by hand is like writing your application in assembly code.

[Marin Capranov]

Example input:

These are polylines from the JSON files. Like: "points" : "{kd_IljoJ" , "points" : "{kd_IljoJd@L|Ab@pA\\r@P", "points" : "qcd_InmoJBSNoAd@}DVsBJk@He@@ERiAPeA@MFi@BMFa@Lu@Hk@",  "points" : "mgc_IltnJLe@DI|B}ELU" ... These are polylines in a order and expected output.

And now that's the actual output: "points": "{kd_IljoJ"

As you can see only the first value and stops there.

I played around with the JSON and noticed that when I change the int value of the getJSONObject(0) ti (1) it gives consequent output. That means that I have to somehow loop through all of the getJSONObject(i), but I can't make it work.

That's the JSON itself for you to have a look at ->
https://gist.github.com/Biseamon/dad9e9c5b91b68d4caebcfa8af7a7eb8

[Marin Capranov]

Regarding the Jackson, I will have a look right now? but if you got any helpful docs I would highly appreciate that.

[Stephan van Hulst]

The problem is that you're only getting the steps of the first leg, and the first leg only has one step.

You probably want to get the steps of all legs of all routes.

Here is the JSON-B user guide. It's not very difficult to use: http://json-b.net/docs/user-guide.html

[Marin Capranov]

So far I have done some changes and it seems to work, however it shows the polylines as straight lines which is strange. Aslo, I don't know how to test the code to see if the loop doesn't return duplicate values. Is there a way to check that?

Thank you for your recommendations by the way. I might look into JSON-B eventually if I won't make it with this one current.

 public void prs(String s){
        PolylineOptions polylineOptions = new PolylineOptions();
        List<LatLng> movements = new ArrayList<>();
       // List<String> points = new ArrayList<>();
        String point = "";

        try {
            JSONObject json = new JSONObject(s);
            JSONArray jsonRoute = json.getJSONArray("routes");

            int count = jsonRoute.length();

            for (int i = 0; i < count; i++) {
                JSONObject jsonObject = jsonRoute.getJSONObject(i);
                JSONArray jsonArray = jsonObject.getJSONArray("legs");
                int count1 = jsonArray.length();
                for (int j = 0; j < count1; j++) {
                    JSONObject jsonObject1 =jsonArray.getJSONObject(j);
                    JSONArray jsonArray1 = jsonObject1.getJSONArray("steps");
                    int count2 = jsonArray1.length();
                    for (int k = 0; k < count2; k++) {
                        JSONObject jsonObject2 = jsonArray1.getJSONObject(i);
                        point = jsonObject2.getJSONObject("polyline").getString("points");
                        movements.addAll(PolyUtil.decode(point));
                    }
                }
            }

[Stephan van Hulst]

Marin Capranov wrote:it shows the polylines as straight lines which is strange.

I can't comment to this because I don't know the PolyUtil.decode implementation, nor do I know what you do with the movements list afterwards.

Aslo, I don't know how to test the code to see if the loop doesn't return duplicate values. Is there a way to check that?

Duplicate values for what? Points on the map? Why wouldn't you allow duplicates? Is it not possible to arrive at the same point on the map twice?

Note that flattening the routes and legs to a single list of points will make it look like the ending point of one leg is also the starting point of the next leg. I'm not sure this is what you want.

[Marin Capranov]

Thank you for your hints. They helped me to find solutions and now I can move to the next phase, which is the genetic algorithm =)