How to convert list of JSON objects to JsonArray and then iterate on it?

Question

I'm trying to convert a string (every JSON object is separated by commas, but first JSON object is the description of this collection) with JSON objects to JsonArray and then I'm trying to iterate on some subelement of each JsonElement, but every single attempt ends up with an error.

String example:

{"type":"FeatureCollection","metadata":{"generated":1554314439000,"url":"https://earthquake.usgs.gov/fdsnws/event/1/query?format=geojson&eventtype=earthquake","title":"USGS Earthquakes","status":200,"api":"1.7.0","count":8970},"features":[{"type":"Feature","properties":{"mag":2.2,"place":"84km SSE of Old Iliamna, Alaska","time":1554313967537,"updated":1554314345998,"tz":-540,"url":"https://earthquake.usgs.gov/earthquakes/eventpage/ak0194a3ew0w","detail":"https://earthquake.usgs.gov/fdsnws/event/1/query?eventid=ak0194a3ew0w&format=geojson","felt":null,"cdi":null,"mmi":null,"alert":null,"status":"automatic","tsunami":0,"sig":74,"net":"ak","code":"0194a3ew0w","ids":",ak0194a3ew0w,","sources":",ak,","types":",geoserve,origin,","nst":null,"dmin":null,"rms":0.74,"gap":null,"magType":"ml","type":"earthquake","title":"M 2.2 - 84km SSE of Old Iliamna, Alaska"},"geometry":{"type":"Point","coordinates":[-154.542,59.0119,127.6]},"id":"ak0194a3ew0w"},

{"type":"Feature","properties":{"mag":1.1,"place":"107km W of Cantwell, Alaska","time":1554313769466,"updated":1554313953376,"tz":-540,"url":"https://earthquake.usgs.gov/earthquakes/eventpage/ak0194a3e7ki","detail":"https://earthquake.usgs.gov/fdsnws/event/1/query?eventid=ak0194a3e7ki&format=geojson","felt":null,"cdi":null,"mmi":null,"alert":null,"status":"automatic","tsunami":0,"sig":19,"net":"ak","code":"0194a3e7ki","ids":",ak0194a3e7ki,","sources":",ak,","types":",geoserve,origin,","nst":null,"dmin":null,"rms":0.63,"gap":null,"magType":"ml","type":"earthquake","title":"M 1.1 - 107km W of Cantwell, Alaska"},"geometry":{"type":"Point","coordinates":[-151.0662,63.2378,7.8]},"id":"ak0194a3e7ki"},

I've tried:

JsonArray jsonObject = new JsonParser()
                    .parse(result)
                    .getAsJsonArray();
List<String> names = new ArrayList<>();
for (JsonElement jsonElement : jsonObject) {
    names.add(jsonElement.getAsJsonObject().get("properties").getAsString());

Answer 1

In case you are in a JavaEE project you are good to go, but if you are in a JavaSE project you need to add these dependencies.

For example, using maven:

<dependencies>
        <dependency>
            <groupId>org.glassfish</groupId>
            <artifactId>javax.json</artifactId>
            <version>1.1</version>
        </dependency>
        <dependency>
            <groupId>org.glassfish.jersey.core</groupId>
            <artifactId>jersey-client</artifactId>
            <version>2.25.1</version>
        </dependency>
</dependencies>

And here it is the code:

• First line, calling your url.
• Second line, processing response as json.

public void loadData() {
        Response response = ClientBuilder.newClient().target("https://earthquake.usgs.gov")
                .path("/fdsnws/event/1/query")
                .queryParam("format", "geojson")
                .queryParam("eventtype", "earthquake")
                .request()
                .get();

        Json.createReader((InputStream) response.getEntity())
                .readObject().getJsonArray("features")
                .stream()
                .map(JsonValue::asJsonObject)
                .map(jsonObject -> jsonObject.getJsonObject("properties"))
                .forEach(System.out::println);
}

As you can see this code prints on screen every single JsonObject called "properties" inside an array called "features".

Important: Be aware that string example you gave in your question is not a valid JSON. Use the one returned by url.

Answer 2

earthquake.usgs.gov API returns payload in GeoJSON format. There is geogson library which implements all needed adapters. You need to only add dependency:

<dependency>
   <groupId>com.github.filosganga</groupId>
   <artifactId>geogson-core</artifactId>
   <version>1.2.21</version>
</dependency>

and below you can find simple example how to use it:

import com.github.filosganga.geogson.gson.GeometryAdapterFactory;
import com.github.filosganga.geogson.model.FeatureCollection;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;

public class GsonApp {

    public static void main(String[] args) throws Exception {
        URL url = new URL("https://earthquake.usgs.gov/fdsnws/event/1/query?format=geojson&eventtype=earthquake");
        URLConnection yc = url.openConnection();
        BufferedReader in = new BufferedReader(new InputStreamReader(yc.getInputStream()));

        Gson gson = new GsonBuilder()
                .registerTypeAdapterFactory(new GeometryAdapterFactory())
                .create();

        FeatureCollection collection = gson.fromJson(in, FeatureCollection.class);
        collection.features().forEach(f -> {
            System.out.println(f.properties());
        });
    }
}

Above app prints:

null, cdi=null, url="https://earthquake.usgs.gov/earthquakes/eventpage/us1000jimv", ids=",us1000jimv,", time=1552230050190, detail="https://earthquake.usgs.gov/fdsnws/event/1/query?eventid=us1000jimv&format=geojson", updated=1553025676040, status="reviewed"}
{dmin=0.01354, code="73150236", sources=",nc,", tz=-480, mmi=null, type="earthquake", title="M 0.3 - 8km WNW of Cobb, CA", magType="md", nst=10, sig=2, tsunami=0, mag=0.32, alert=null, gap=159, rms=0.02, place="8km WNW of Cobb, CA", net="nc", types=",geoserve,nearby-cities,origin,phase-data,scitech-link,", felt=null, cdi=null, url="https://earthquake.usgs.gov/earthquakes/eventpage/nc73150236", ids=",nc73150236,", time=1552229803430, detail="https://earthquake.usgs.gov/fdsnws/event/1/query?eventid=nc73150236&format=geojson", updated=1552436044263, status="reviewed"}
{dmin=0.0134, code="73150231", sources=",nc,", tz=-480, mmi=null, type="earthquake", title="M 0.6 - 8km WNW of Cobb, CA", magType="md", nst=9, sig=5, tsunami=0, mag=0.57, alert=null, gap=152, rms=0.01, place="8km WNW of Cobb, CA", net="nc", types=",geoserve,nearby-cities,origin,phase-data,scitech-link,", felt=null, cdi=null, url="https://earthquake.usgs.gov/earthquakes/eventpage/nc73150231", ids=",nc73150231,", time=1552229731210, detail="https://earthquake.usgs.gov/fdsnws/event/1/query?eventid=nc73150231&format=geojson", updated=1552235523281, status="automatic"}
....