Extracting data from RESTful API to parse as json and extract data from there JAVA

Question

I am dealing with a pretty old API provided from KhanAcademy.

Link to git: https://github.com/Khan/khan-api/wiki/Khan-Academy-API

I don't have any experience consuming REST services or how to parse Json from them. I have tried what I could find online but most SO posts or other things on the internet don't involve handling both REST and json at the same time. I have tried mapping the json to a map but I couldn't get that to work due to my Json queries not being processed properly.

Here are some bits of code that I have tried using:

public static Object getConnection(String url){
    URL jsonUrl;
    String message;
    try{
        jsonUrl = new URL(url);
        System.out.println("This is the URL: "+ jsonUrl);
    } catch (MalformedURLException ex) {
        message = "failed to open a new conenction. "+ ex.getMessage();
        //logger.warn(message);
        throw new RuntimeException();
    }
    URLConnection connection;
    try{
        connection = jsonUrl.openConnection();
        connection.connect();
    }catch(IOException e){
        message = "Failed to open a new connection. " + e.getMessage();
        //logger.warn(message);
        throw new RuntimeException();
    }


    Object jsonContents;
    try{
        jsonContents = connection.getContent();


        System.out.println("This is the content: "+jsonContents);
    }catch(IOException e){
        message = "failed to get contents.";
        //logger.warn(message);
        throw new RuntimeException(message);
    }
    return jsonContents;
    }

the below is using JAX RS API

    Client client = ClientBuilder.newClient();
    WebTarget target = client.target("http://www.khanacademy.org/api/v1/topictree");
    JsonArray response = target.request(MediaType.APPLICATION_JSON).get(JsonArray.class);

}

The below is some "Zombie code", it is a compilation of things I have tried mainly shown to verify that I am truly lost and that I have been looking for a solution for about 7 hours now?


    JsonReader reader = new JsonReader(response);
    JsonParser parser = new JsonParser();

    JsonElement rootElement = parser.parse(reader);
    JsonElement rootElement = parser.parse(response.getAsString());
    JsonArray jsonArray = rootElement.getAsJsonArray();
    ArrayList results = new ArrayList();
    Gson myGson = new Gson();
    for(JsonElement resElement : jsonArray){
       //String mp4 = myGson.fromJson(resElement, );
   }
    JsonArray jarray =jsonObject.getAsJsonArray();

    jsonObject= jarray.get(0).getAsJsonObject();
    String result = jsonObject.get("title").getAsString();
    System.out.println(result);
    JsonObject resultObject = jsonObject.getAsJsonObject("url");
    String result = resultObject.getAsString();
    System.out.println(result);
    JsonObject jsonObject=response.get(0).getAsJsonObject();

    return new Gson().fromJson(url, mapType);
}

Any help is appreciated.

What do you want to extract from the json result after making the API call? — Karan
– Karan, Commented Apr 3, 2019 at 0:29
@Karan Hi Karan, thanks for replying. If I may show you this: [link]api-explorer.khanacademy.org/api/v1/topic[link]. I would like to get all the youtube links/ mp4 urls for a topic/subject the user chooses.I originally pointed my browser at [link]khanacademy.org/api/v1/topic[link] /<topic name>. Issue probably lies with me in not knowing what to do with a parsed json. I also found that searching by topic often meant there was no result so instead I tried pointing at this: [link]khanacademy.org/api/v1/topictree[link] — Robert Vasistha
– Robert Vasistha, Commented Apr 3, 2019 at 5:39

earandap · Accepted Answer · 2019-04-03 03:55:44Z

2

You can use Feign to do it.

I recommend you create Java classes for representing the JSON structure, which is defined here

Here a basic demo:

public class App {
    public static void main(String[] args) {
        KhanAcademyAPI khanAcademyAPI = Feign.builder()
                .decoder(new GsonDecoder())
                .logLevel(Logger.Level.HEADERS)
                .target(KhanAcademyAPI.class, "http://www.khanacademy.org");


        Topic root = khanAcademyAPI.tree();
        root.children.forEach(topic1 -> System.out.println(topic1.slug));

        Topic science = khanAcademyAPI.topic("science");
        science.children.forEach(topic1 -> System.out.println(topic1.description));

    }

    public static class Topic {
        String description;
        boolean hide;
        String slug;
        List<Topic> children;
    }

    interface KhanAcademyAPI {
        @RequestLine("GET /api/v1/topictree")
        Topic tree();

        @RequestLine("GET /api/v1/topic/{topic_slug}")
        Topic topic(@Param("topic_slug") String slug);
    }
}

I used the following maven dependencies only:

io.github.openfeign:feign-core:10.2.0
io.github.openfeign:feign-gson:10.2.0

edited Apr 3, 2019 at 3:55

answered Apr 3, 2019 at 3:43

earandap

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1 Comment

Robert Vasistha Over a year ago

You are a thing of beauty. Thank you so much. I am surprised to not see this anywhere else on the internet without searching for Feign specifically. You can't imagine the troubles I have had with trying to work with this.

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