how to Convert from json to java object?

Question

I have a get request with the response of json like bellow:

{"version": 0.6, "generator": "Overpass API", "osm3s": { "timestamp_osm_base": "", "copyright": "The data included in this document is from www.openstreetmap.org. The data is made available under ODbL." }, "elements": [ { "type": "node", "id": 25941318, "lat": 35.7006285, "lon": 51.3909900 }, { "type": "node", "id": 26839944, "lat": 35.7006369, "lon": 51.3913739 }, { "type": "node", "id": 1333387625, "lat": 35.7012370, "lon": 51.3913564 } ] }

I need to convert this Json to java object, this is my model class:

package com.findItntersection.model; public class Intersection { String type; private long id; private double lon; private double lat; public String getType() { return type; } public void setType(String type) { this.type = type; } public long getId() { return id; } public void setId(long id) { this.id = id; } public double getLon() { return lon; } public void setLon(double lon) { this.lon = lon; } public double getLat() { return lat; } public void setLat(double lat) { this.lat = lat; } @Override public String toString() { return "elements [ type=" + type + ",id=" + id + ",lon=" + lon + ".lat" + lat + "]"; }}

and my service method which sends get request correctly:

public void sendGet(String city, String street1, String street2) throws ClientProtocolException, IOException, URISyntaxException { Gson gson = new Gson(); URIBuilder builder = new URIBuilder(); builder.setScheme("http") .setHost("192.168.0.67") .setPath("/api/interpreter") .setParameter( "data", "[out:json];area[name~\"" + city + "\"]->.b;way(area.b)[highway][name~\"" + street1 + "\"];node(w)->.n1;way(area.b)[highway][name~\"" + street2 + "\"];node(w)->.n2;node.n1.n2;out;"); URI uri = builder.build(); CloseableHttpClient httpclient = HttpClients.createDefault(); HttpGet httpGet = new HttpGet(uri); CloseableHttpResponse response1 = httpclient.execute(httpGet); try { System.out.println(response1); HttpEntity entity1 = response1.getEntity(); String json = EntityUtils.toString(entity1,"UTF-8"); Intersection fromJson = gson.fromJson(json, Intersection.class); System.out.println(fromJson); EntityUtils.consume(entity1); } finally { response1.close(); } }

but the fromJson is like this: [ type=null,id=0,lon=0.0.lat0.0]

the result from get request json:

{ "version": 0.6, "generator": "Overpass API", "osm3s": { "timestamp_osm_base": "", "copyright": "The data included in this document is from www.openstreetmap.org. The data is made available under ODbL." }, "elements": [ { "type": "node", "id": 29004231, "lat": 35.7212341, "lon": 51.3888708 } ] }

Can anybody help me please?

do you get the right result from ur get request? (i.e. do you get ur desired jsonObject) — nafas
– nafas, Commented Mar 11, 2015 at 11:22

Cem Özer · Accepted Answer · 2015-03-11 11:44:44Z

Gson cannot parse because your response is not a representation of Intersection class.

It represents something like that:

public class OsmResult implements Serializable{ private double version; private String generator; private HashMap<String, String> osm3s; private ArrayList<Intersection> elements; ...getters & setters }

From here, you can go two ways;

Extract elements and parse it to a Intersection list.

I think there is no extraction method in Gson but you can try other Json libraries for that. Or, you can do simple String operations to extract elements.

Parse it to a class like above and just use getElements() method.

If you stick with Gson, I recommend that as it is more cleaner way to do it.

sarveshseri · Accepted Answer · 2015-03-11 11:39:21Z

That's because your response is not an Intersection. It is an object which contains an array of Intersections.

So, you first need to convert the JSON to a JsObject, then get this array and convert it to List of Intersections.

String json = EntityUtils.toString(entity1,"UTF-8"); JsonParser jp = new JsonParser(); JsonObect jo = ( JsonObject ) jp.parse( json ); // JsonArray of intersection JsonElement's JsonArray ija = ( JsonArray ) jo.get( "elements" ); // Iterator of intersection JsonElements Iterator<JsonElement> iji = ija.iterator(); List< Intersection> il = new ArrayList< Intersection >(); while( iji.hasNext() ) { JsonElement je = iji.next(); // convert to Intersection Intersection i = gson.fromJson( je, Intersection.class ); // add to List il.add( i ); } // do whatever you want with your list of intersections.

Sarah · Accepted Answer · 2015-03-11 11:31:25Z

This is because your model class is not correct. Class Intersection just maps the elements in json. You should have a model class which maps all the json elements , with "Elements" as another class defining its own elements.

http://www.journaldev.com/2324/jackson-json-processing-api-in-java-example-tutorial

This example should help.

I have also tried this in my model: @Override public String toString() { return " {\n \"version\": 06,\n \"generator\": \"Overpass API\",\n \"osm3s\" : {\n \"timestamp_osm_base\": \"\" ,\n \"copyright\": \"The data included in this document is from www.openstreetmap.org. The data is made available under ODbL.\"\n}," + "\n \"elements\" : [\n\n{\n \"type\" : " + type + ",\n \"id\" : " + id + ",\n \"lat\" : " + lat + ",\n \"lon\" : " + lon + "}]}";} but didn't work

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