How to parse overpassAPI http response contents into variables

Question

Http query to overpassAPI is working but I have tried many different approaches to programatically convert the response (very long string) into anything useful.

Tried line by line, substrings, etc in all manner of combinations but still cant find anything that works as I need it to:

take response string, find first "item" & store type (e.g 'way' or 'node'), then make variables (possibly string arraylist) of the names and values of each item element (eg [id, lat, lon, timestamp]... and [000001, 50, 50, 12:00,]... etc) so i can use them as output values to the user. There may not always be the same amount of items in the list for each item, hence i have been failing to use various loops to achieve this so far.

I have no preference in either XML or JSON response format as all I need are the values.

Can someone suggest code to achieve this? Or at least suggest somewhere that has the answers I'm looking for?

I've wasted nearly an entire day trying to figure it out myself and googling for a solution so far

Many thanks

score 0 · Answer 1 · answered Jan 15 '20 at 16:38

I don’t know that specific API but overall you mostly never want to parse the string yourself. Search a library to parse either json or xml and you will be able to manipulate the answer to retrieve the specific data of your choice.

I mostly use json and most libraries let you access the data like a hash map once it is parsed.

As they are loads of libraries existing for that job, I don’t want to recommend one in particular as it might no longer be maintained in a year or not correspond to your preference.

score 0 · Accepted Answer · answered Jan 28 '20 at 11:16

hopefully this will save someone else the agonisizing headache this caused me: solved after about 7-8 hours of trial-and-error:


public void responseParse(String response) {
    try {
        //get json object from (whole) response string
        JSONObject responseObj = new JSONObject(response);
        //pull out jsonArray (of elements) from object
        JSONArray responseArr = responseObj.getJSONArray("elements");
        Log.d(TAG, "responseParse: Elements: " + responseArr);

        //empty previous road list
        roadArrList = new ArrayList<>();

        //for each element item in json array
        for (int i = 0; i < responseArr.length(); i++) {
            //convert element to string of contents
            String elementStr = responseArr.getString(i);
            //create individual element object from (whole) element string
            JSONObject elementObj = new JSONObject(elementStr);

            //pass element (road) for road data string extraction (and adding to list)
            getCardData(elementObj);

        }
    } catch (Exception e) {
        Log.e(TAG, "responseParse: error: json parsing;");
        //todo: handle error
        e.printStackTrace();
    }

    //set recyclerView with road cards
    buildRecyclerView();
}

element object is passed to recyclerView building method:

public void getCardData(JSONObject elementObj) {
        //pull out jsonObject (of tags) from element
        try {
            JSONObject tagObj = elementObj.getJSONObject("tags");
        } catch (JSONException e) {
            Log.e(TAG, "getCardData: error creating tag json object");
            e.printStackTrace();
        }

        //assign road name
        try {
            //for each element, get its required tags and get string of value
            roadName = elementObj.getJSONObject("tags").getString("name");
            Log.d(TAG, "responseParse: ROADNAME RETRIEVED: " + roadName);
        } catch (JSONException e) {
            Log.w(TAG, "responseParse: JSON exception occurred: no NAME for road");
            roadName = "NO ROAD NAME AVAILABLE";
        }

        //assign road ID
        try {
            roadId = elementObj.getString("id");
            Log.d(TAG, "responseParse: ID RETRIEVED: " + roadId);
        } catch (JSONException e) {
            Log.w(TAG, "responseParse: JSON exception occurred: no ID for road");
            roadId = "NO ROAD ID AVAILABLE";
        }

        //assign road limit
        try {
            roadLimit = elementObj.getJSONObject("tags").getString("maxspeed");
            Log.d(TAG, "responseParse: SPEED RETRIEVED: " + roadLimit);
        } catch (JSONException e) {
            Log.w(TAG, "responseParse: JSON exception occurred: no SPEED for road");
            roadLimit = "NO ROAD LIMIT AVAILABLE";
        }

        //add element (road) values into array (new card)
        roadArrList.add(new CardRoad(R.drawable.ic_road, roadName, roadId, roadLimit));
    }

How to parse overpassAPI http response contents into variables

2 Answers2