Deserialize JSON with Gson in an object

Question

I have a JSON string such as below. That comes from a Website (the URL outputs below to a page) which I'm using in an android application.

{"posts": [{"id":"0000001","longitude":"50.722","latitude":"-1.87817","position":"Someplace 1","altitude":"36","description":"Some place 1 "},{"id":"0000002","longitude":"50.722","latitude":"-1.87817","position":"Some PLace 2","altitude":"36","description":"Some place 2 description"}]}

I would like to deserialize this into a List where I can iterate through them later on the application. How do I do this? I have created a class with properties and methods and a List class as below and then using fromJson to deserialize it, but it returns NULL. Hope the question is clear and many thanks in advance.

ListClass

package dataaccess;

import java.util.List;

public class LocationList {
    public static List<Location> listLocations;

    public void setLocationList(List <Location> listLocations) {
        LocationList.listLocations = listLocations;
    }

    public List<Location> getLocationList() {
        return listLocations;
    }
}

GSON

public LocationList[] getJsonFromGson(String jsonURL) throws IOException{
    URL url = new URL(jsonURL);
    String content = IOUtils.toString(new InputStreamReader(url.openStream()));
    LocationList[] locations =  new Gson().fromJson(content, LocationList[].class);

    return locations;
}

Yogu · Accepted Answer · 2011-11-06T16:55:59.310

2

You try to deserialize into an array of LocationList objects - that surely wasn't your intent, was it? The json snippet doesn't contain a list of lists.

I would drop the class LocationList (except it ought to be extened in future?), and use a pure List. Then, you have to create a type token like this:

java.lang.reflect.Type type = new com.google.gson.reflect.TypeToken<ArrayList<Location>>() {}.getType();
List<Location> locations = new Gson().fromJson(content, type);

edited Nov 06 '11 at 16:55

answered Nov 06 '11 at 16:22

Yogu

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Thanks for the answer. What's the namespace for Type and TypeToken? – Dev Nov 06 '11 at 16:28
eclipse flags java.lang.Type as invalid. However, import java.lang.reflect.Type; is fine. Is that what you've meant? – Dev Nov 06 '11 at 16:39
Tried doing this, However, now get a new "Source not found" on Gson Library. I can assure you that the library is added to the build path. – Dev Nov 06 '11 at 17:25
Is it a compile-time error or an exception? Does it still occur, when you change back code to the version you posted? How about restarting Eclipse? – Yogu Nov 06 '11 at 17:44
let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/4765/discussion-between-chin-and-yogu) – Dev Nov 06 '11 at 17:54
@Yogu- yes it did work.. many thanks...sorry for the late reply – Dev Nov 10 '11 at 20:48

score 2 · Answer 2 · answered Nov 06 '11 at 19:30

What if this JSON response can be parsed using native classes, here is a solution for the same:

String strJsonResponse="Store response here";
JsonObject obj = new JsonObject(strJsonResponse);
JsonArray array = obj.getJsonArray("posts");

for(int i=0; i<array.length; i++)
{
   JsonObject subObj = array.getJsonObject(i);
   String id = subObj.getString("id");
   String longitude = subObj.getString("longitude");
   String latitude = subObj.getString("latitude");
   String position = subObj.getString("position");
   String altitude = subObj.getString("altitude");
   String description = subObj.getString("description");

   // do whatever procedure you want to do here
}

Deserialize JSON with Gson in an object

2 Answers2