How to convert a json file that contains multiple objects to a list of java objects using json

Question

I'm working on a Java project that fetches the URL of the most popular clips of the day on Twitch. To do this I'm sending a request to the twitch API with this code:

    private List<TwitchClip> getVideoList() {
    try {
        LocalTime midnight = LocalTime.MIDNIGHT;
        LocalDate today = LocalDate.now(ZoneId.of("Europe/Berlin"));
        LocalDateTime todayMidnight = LocalDateTime.of(today, midnight);

        String formattedStartTime;
        String formattedEndTime;
        if(String.valueOf(todayMidnight.getMonthValue()).length() != 2) {
            formattedStartTime = todayMidnight.getYear() + "-" + 0 + todayMidnight.getMonthValue() + "-" + (todayMidnight.getDayOfMonth() - 1) + "T00:00:00Z";
            formattedEndTime = todayMidnight.getYear() + "-" + 0 + todayMidnight.getMonthValue() + "-" + todayMidnight.getDayOfMonth() + "T00:00:00Z";
        }else {
            formattedStartTime = todayMidnight.getYear() + "-" + todayMidnight.getMonthValue() + "-" + (todayMidnight.getDayOfMonth() - 1) + "T00:00:00Z";
            formattedEndTime = todayMidnight.getYear() + "-" + todayMidnight.getMonthValue() + "-" + todayMidnight.getDayOfMonth() + "T00:00:00Z";
        }

        URL url = new URL("https://api.twitch.tv/helix/clips?game_id=" + Game.FORTNITE.getId() + "&first=25&started_at=" + formattedStartTime + "&ended_at=" + formattedEndTime);
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        connection.setRequestMethod("GET");
        connection.addRequestProperty("Client-ID", "");

        File out = File.createTempFile(UUID.randomUUID().toString(), ".json");
        System.out.println("Downloaded clips data at " + out.getPath());
        writeFile(out, connection.getInputStream());

        Gson gson = new Gson();
        return gson.fromJson(new FileReader(out), new TypeToken<List<TwitchClip>>() {
        }.getType());
    } catch (IOException e) {
        e.printStackTrace();
        return null;
    }
}

which returns a json file that looks like this:

{"data":[{"id":"HeadstrongObservantEagleANELE","url":"https://clips.twitch.tv/HeadstrongObservantEagleANELE","embed_url":"https://clips.twitch.tv/embed?clip=HeadstrongObservantEagleANELE","broadcaster_id":"81687332","broadcaster_name":"cloakzy","creator_id":"158774890","creator_name":"xvibes","video_id":"442904759","game_id":"33214","language":"en","title":"creatorcode: cloakzy !mouse","view_count":11755,"created_at":"2019-06-23T01:05:51Z","thumbnail_url":"https://clips-media-assets2.twitch.tv/34634505760-offset-684-preview-480x272.jpg"},{"id":"LongSpineyYakinikuPogChamp","url":"https://clips.twitch.tv/LongSpineyYakinikuPogChamp","embed_url":"https://clips.twitch.tv/embed?clip=LongSpineyYakinikuPogChamp","broadcaster_id":"81687332","broadcaster_name":"cloakzy","creator_id":"57403631","creator_name":"4rchr","video_id":"442904759","game_id":"33214","language":"en","title":"x","view_count":10204,"created_at":"2019-06-23T01:08:48Z","thumbnail_url":"https://clips-media-assets2.twitch.tv/34634505760-offset-860-preview-480x272.jpg"},{"id":"SuspiciousMistyTortoiseImGlitch","url":"https://clips.twitch.tv/SuspiciousMistyTortoiseImGlitch","embed_url":"https://clips.twitch.tv/embed?clip=SuspiciousMistyTortoiseImGlitch","broadcaster_id":"81687332","broadcaster_name":"cloakzy","creator_id":"139090954","creator_name":"Malgre","video_id":"442904759","game_id":"33214","language":"en","title":"cloak","view_count":8104,"created_at":"2019-06-23T01:12:36Z","thumbnail_url":"https://clips-media-assets2.twitch.tv/AT-cm%7C481623363-preview-480x272.jpg"}],"pagination":{"cursor":"eyJiIjpudWxsLCJhIjp7IkN1cnNvciI6Ik13PT0ifX0"}}

Although, I'm getting this error:

Exception in thread "Timer-0" com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was BEGIN_OBJECT at line 1 column 2 path $
    at com.google.gson.Gson.fromJson(Gson.java:939)
    at com.google.gson.Gson.fromJson(Gson.java:892)
    at video.TwitchVideo.getVideoList(TwitchVideo.java:104)
    at video.TwitchVideo.<init>(TwitchVideo.java:19)
    at main.TwitchApplication$1.run(TwitchApplication.java:56)
    at java.util.TimerThread.mainLoop(Unknown Source)
    at java.util.TimerThread.run(Unknown Source)
Caused by: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was BEGIN_OBJECT at line 1 column 2 path $
    at com.google.gson.stream.JsonReader.beginArray(JsonReader.java:350)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:80)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61)
    at com.google.gson.Gson.fromJson(Gson.java:927)
    ... 6 more

score 0 · Accepted Answer · answered Jun 23 '19 at 17:12

0

As you can see from your json with the { data: [{...}, {...}, {...}], pagination: {...} }, you get a object. You tried to read a array, but not the object that is given. This object has an array data and an object pagination.

Assuming that your object TwitchData only contains the attributes from the data array, you could work with the following solution.

class Result {
    TwitchData[] data;
    Pagination pagination;
}

class Pagination{
    String cursor;
}

After you created the two classes, you can now read the json.

Result r = gson.fromJson(new FileReader(out), Result.class);
return r.data;

This will return you the data array which can also be transfomed into a List if you wish so.

answered Jun 23 '19 at 17:12

alea

980
1
13
18

I followed your instruction, but when I try to get the array I get null – Auties01 Jun 23 '19 at 17:31
I just noticed that the cursor value is correct while the clips are null – Auties01 Jun 23 '19 at 17:38
Never Mind I missed spelled data(how?), now it all works! – Auties01 Jun 23 '19 at 17:46

How to convert a json file that contains multiple objects to a list of java objects using json

1 Answers1