Parsing JSON in JAVA usng Gson

Question

So I am trying to parse a JSON object in Java using Gson. I am trying to consume an API from a website. This is the ticker: https://api.coinmarketcap.com/v1/ticker/bitcoin/

The JSON looks like this:

[
    {
        "id": "bitcoin", 
        "name": "Bitcoin", 
        "symbol": "BTC", 
        "rank": "1", 
        "price_usd": "3591.95", 
        "price_btc": "1.0", 
        "24h_volume_usd": "3263990000.0", 
        "market_cap_usd": "59516499433.0", 
        "available_supply": "16569412.0", 
        "total_supply": "16569412.0", 
        "percent_change_1h": "1.02", 
        "percent_change_24h": "15.59", 
        "percent_change_7d": "-15.18", 
        "last_updated": "1505563475"
    }
]

I am using Jersey for consuming the API and I want to transform this JSON into an object.

This is the object that should be built by parsing the JSON:

public class CryptoCurrency {

    String id;
    String name;
    String symbol;
    String rank;
    String price_usd;
    String price_btc;
    String market_cap_usd;
    String available_supply;
    String total_supply;
    String percent_change_1h;
    String percent_change_24h;
    String percent_change_7d;
    String last_updated;

}

This is my code:

public class CoinMarketCap {

    public static void main(String[] args) {
        Client client = ClientBuilder.newClient();
        WebTarget target = client.target("https://api.coinmarketcap.com/v1/ticker/bitcoin/");
        String bitoinDeteils = target.request(MediaType.TEXT_XML).get(String.class);
        Gson gson = new GsonBuilder().create(); 
        CryptoCurrency bitcoin = gson.fromJson(bitoinDeteils, CryptoCurrency.class);
        System.out.println(bitcoin);

    }
}

I Get an error

Exception in thread "main" com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was BEGIN_ARRAY at line 1 column 2 path $ at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:224) at com.google.gson.Gson.fromJson(Gson.java:887) at com.google.gson.Gson.fromJson(Gson.java:852) at com.google.gson.Gson.fromJson(Gson.java:801) at com.google.gson.Gson.fromJson(Gson.java:773) at com.randomizer.CoinMarketCap.main(CoinMarketCap.java:21) Caused by: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was BEGIN_ARRAY at line 1 column 2 path $ at com.google.gson.stream.JsonReader.beginObject(JsonReader.java:385) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:213) ... 5 more

Do you see anything wrong in my code? thanks.

Please show an example JSON too. It seems at some point the JSON contains an array but you try to store it in an object. — juzraai, Sep 16 '17 at 10:51
Possible duplicate of [How to deserialize a JSON array using Gson](https://stackoverflow.com/questions/10292514/how-to-deserialize-a-json-array-using-gson). Your JSON is an array containing just one object, so you need to deserialize the array. — Aleksei Budiak, Sep 16 '17 at 11:04
1) Why are you requesting XML and trying to parse JSON? 2) Print `bitcoinDetails`. What is it? — Paul Samsotha, Sep 16 '17 at 11:49
this is the JSON as string. I want to deserialize it into an object. — NotSure, Sep 16 '17 at 12:12

score 1 · Accepted Answer · answered Sep 16 '17 at 12:23

1

The error message says that the JSON string contains an array ("was BEGIN_ARRAY"), but you try it parse it as an object ("Expected BEGIN_OBJECT").

As we can see in the JSON string you provided, it's indeed an array, the object you're interested in is wrapped in square brackets ([ ... ]).

Try to parse it for example as a List<CryptoCurrency> then:

Type listType = new TypeToken<ArrayList<CryptoCurrency>>(){}.getType();
List<CryptoCurrency> list = new Gson().fromJson(jsonString, listType);

(Type is java.lang.reflect.Type.)

answered Sep 16 '17 at 12:23

juzraai

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Yes you are right. I was new to JSON to I didn't even see that the only object is inside an array. I've ended up just taking my code and making my Wrapper (named CryptoCurrency) an array. what I changed was : CryptoCurrency[] arr = gson.fromJson(bitoinDeteils, CryptoCurrency[].class); and then just accesing CryptoCurrency[0] – NotSure Sep 16 '17 at 12:46

Parsing JSON in JAVA usng Gson

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