如何使用Retrofit 2（+ Nested对象）解析动态JSON

Question

我正在尝试解析看起来像这样的JSON响应。

{
    "Cryptsy": {
        "AMC": [
            "BTC"
        ],
        "CIRC": [
            "BTC"
        ],
        "SYNC": [
            "BTC"
        ]
    },
    "Bitstamp": {
        "EUR": [
            "USD"
        ],
        "ETH": [
            "USD",
            "EUR"
        ],
        "XRP": [
            "USD",
            "EUR",
            "BTC"
        ]
    },
    // ...
    // More objects...
    // ...
}

如您所见，该对象具有动态键，每个值也是具有动态键的对象。 我尝试使用Retrofit2和GsonConverter解析它，但它导致异常

W/System.err: java.lang.IllegalStateException: Expected a string but was BEGIN_OBJECT at line 1 column 2 path $

我认为这是因为JSON是嵌套的，并且所有对象都没有任何固定键。

这是我的代码。

PairListResponse.java

// This is the GSON model class

class PairListResponse {

    private Map<String, Map<String, String[]>> exchangePairs;

    PairListResponse() {
    }

    Map<String, Map<String, String[]>> getExchangePairs() {
        return exchangePairs;
    }

    void setExchangePairs(Map<String, Map<String, String[]>> exchangePairs) {
        this.exchangePairs = exchangePairs;
    }

    Map<String, String[]> getTradingPairs(String fromSymbol) {
        return exchangePairs.get(fromSymbol);
    }
}

PairListDeserializer.java

public class PairListDeserializer implements JsonDeserializer<PairListResponse> {

    private static final String TAG = PairListDeserializer.class.getSimpleName();

    @Override
    public PairListResponse deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        final JsonObject jsonObject = json.getAsJsonObject();
        final Map<String, Map<String, String[]>> exchangePairs = readPairMap(jsonObject);
        PairListResponse result = new PairListResponse();
        result.setExchangePairs(exchangePairs);
        return result;
    }

    @Nullable
    private Map<String, Map<String, String[]>> readPairMap(@NonNull final JsonObject jsonObject) {
        // Initializing Hashmap for the outer object
        final Map<String, Map<String, String[]>> result = new HashMap<>();

        for (Map.Entry<String, JsonElement> entry : jsonObject.entrySet()) {
            String exchange = entry.getKey();
            String fromSymbol;
            String[] toSymbols;
            JsonObject fsymbolObj = entry.getValue().getAsJsonObject();

        // Initializing Hashmap for inner objects
            final Map<String, String[]> pairsPerCoin = new HashMap<>();

            for (Map.Entry<String, JsonElement> inner_entry : fsymbolObj.entrySet()) {
                fromSymbol = inner_entry.getKey();
                toSymbols = toStringArray(inner_entry.getValue().getAsJsonArray());
                pairsPerCoin.put(fromSymbol, toSymbols);
            }
            result.put(exchange, pairsPerCoin);
        }
        return result;
    }

    private static String[] toStringArray(JsonArray array) {
        if (array == null) return null;
        String[] arr = new String[array.size()];
        for (int i = 0; i < arr.length; i++) {
            arr[i] = array.get(i).toString();
        }
        return arr;
    }
}

提前致谢！

Answer 1

抱歉，我犯了一个最愚蠢的错误！ 在我的改造API调用中，我忘记设置正确的模型类名称。

public interface TradingPairAPICall {
    @GET("exchanges")
    Call<String> getAllPairList();
}

实际上，它需要

Call<PairListResponse> getAllPairList();

我更改了它，然后成功地工作了。