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

1

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.

answered Mar 11, 2015 at 11:44

Cem Özer

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Comments

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

0

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.

answered Mar 11, 2015 at 11:31

Sarah

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1 Comment

Nazila Over a year ago

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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