java - 使用 GSON 将 JSON 数据解析为数组时出错

Question

在您根据标题认为这个问题是重复的之前，我必须说，我找不到针对我的具体问题的任何解决方案。但是，如果您能建议一些链接，我将不胜感激!也就是说，我的问题是我不断收到以下 GSON 异常:

07-24 10:12:44.713 2540-2603/com.davenotdavid.dndheadlines W/System.err: com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was BEGIN_OBJECT at line 1 column 2 path $

我知道我以某种方式传递 JSON 对象而不是数组，但我不明白的是它如何基于以下实用程序类不起作用，该实用程序类基本上具有解析和提取 JSON 数据的辅助方法使用 OkHttpClient 和 GSON 库从 JSON 数组中提取数据，然后将提取的数据列表返回给调用类:

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;

public class QueryUtils {
    public static List<Article> fetchArticleData(String requestUrl) {
        String jsonResponse = "";
        try {
            OkHttpClient okHttpClient = new OkHttpClient();
            Request request = new Request.Builder()
                    .url(requestUrl)
                    .build();
            Response response = okHttpClient.newCall(request).execute();
            jsonResponse = response.body().string();
        } catch (Exception e) {
            e.printStackTrace();
        }

        return extractDataFromJson(jsonResponse);
    }

    private static List<Article> extractDataFromJson(String jsonResponse) {
        if (jsonResponse == null || jsonResponse.isEmpty()) {
            return null;
        }

        List<Article> articlesList = new ArrayList<>();

        ArticleResponse[] articleResult = new ArticleResponse[0];
        try {
            Gson gson = new Gson();
            Type collectionType = new TypeToken<Collection<ArticleResponse>>(){}.getType();

            // *** Exception is thrown here ***
            Collection<ArticleResponse> enums = gson.fromJson(jsonResponse, collectionType);

            articleResult = enums.toArray(new ArticleResponse[enums.size()]);
        } catch (Exception e) {
            e.printStackTrace();
        }

        if (articleResult.length != 0) {
            for (int i = 0; i < articleResult.length; i++) {
                ArticleResponse article = articleResult[i];
                articlesList.add(new Article(
                        article.getTitle(),
                        article.getUrl(),
                        article.getUrlToImage(),
                        article.getPublishedAt()));
            }
        }

        return articlesList;
    }
}

您会注意到以下代码行引发了异常:

Collection<ArticleResponse> enums = gson.fromJson(jsonResponse, collectionType);

这是我使用 GsonFormat 生成的 ArticleResponse 类:

public class ArticleResponse {

    /**
     * author : Annalee Newitz
     * title : First glimpse of Steven Spielberg’s new movie, Ready Player One
     * description : This trailer introduces us to a VR dystopia, and has the greatest soundtrack ever.
     * url : https://arstechnica.com/the-multiverse/2017/07/first-glimpse-of-steven-spielbergs-new-movie-ready-player-one/
     * urlToImage : https://cdn.arstechnica.net/wp-content/uploads/2017/07/RPO-1000x437-nbv413pszkz7s29g3blop7i6ymcv84f9mtwmvt1xxk-760x380.png
     * publishedAt : 2017-07-23T17:13:56Z
     */

    private String title;
    private String url;
    private String urlToImage;
    private String publishedAt;

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {this.title = title;}

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public String getUrlToImage() {
        return urlToImage;
    }

    public void setUrlToImage(String urlToImage) {
        this.urlToImage = urlToImage;
    }

    public String getPublishedAt() {
        return publishedAt;
    }

    public void setPublishedAt(String publishedAt) {
        this.publishedAt = publishedAt;
    }
}

实用程序类中网络调用的 JSON 响应示例如下:

{
    "status": "ok",
    "source": "ars-technica",
    "sortBy": "top",
    "articles": [{
        "author": "Eric Berger",
        "title": "Elon Musk’s Mars rocket may be about to lose half of its engines",
        "description": "Downscaling the Mars booster suggests that Musk may be bending toward reality.",
        "url": "https://arstechnica.com/science/2017/07/elon-musk-drops-an-important-hint-about-his-revised-mars-rocket/",
        "urlToImage": "https://cdn.arstechnica.net/wp-content/uploads/2017/07/29937260386_45ba70fb85_h-1440x614-760x380.jpg",
        "publishedAt": "2017-07-24T13:12:01Z"
    }, {
        "author": null,
        "title": "Hour of Devastation review: The evil elder dragon god-pharaoh has arrived. RIP.",
        "description": "Plus, a look at the major changes coming to future Magic: the Gathering sets.",
        "url": "https://arstechnica.com/gaming/2017/07/magic-hour-of-devastation-review/",
        "urlToImage": "https://cdn.arstechnica.net/wp-content/uploads/2017/07/401538_CN-copy-760x380.jpg",
        "publishedAt": "2017-07-24T13:00:52Z"
    }, {
        "author": "Annalee Newitz",
        "title": "Season 2 of Stranger Things looks even creepier and more intense",
        "description": "The Upside Down is back, and it looks like it's about to eat the world.",
        "url": "https://arstechnica.com/the-multiverse/2017/07/season-2-of-stranger-things-looks-even-creepier-and-more-intense/",
        "urlToImage": "https://cdn.arstechnica.net/wp-content/uploads/2017/07/landscape-1486986380-stranger-things-mike-wheeler-2-760x380.jpg",
        "publishedAt": "2017-07-23T23:20:39Z"
    }, {
        "author": "Annalee Newitz",
        "title": "First glimpse of Steven Spielberg’s new movie, Ready Player One",
        "description": "This trailer introduces us to a VR dystopia, and has the greatest soundtrack ever.",
        "url": "https://arstechnica.com/the-multiverse/2017/07/first-glimpse-of-steven-spielbergs-new-movie-ready-player-one/",
        "urlToImage": "https://cdn.arstechnica.net/wp-content/uploads/2017/07/RPO-1000x437-nbv413pszkz7s29g3blop7i6ymcv84f9mtwmvt1xxk-760x380.png",
        "publishedAt": "2017-07-23T17:13:56Z"
    }, {
        "author": null,
        "title": "New book explores how protesters—and governments—use Internet tactics",
        "description": "The protest frontiers are changing. An entrenched researcher explains why they work.",
        "url": "https://arstechnica.com/tech-policy/2017/07/twitter-and-tear-gas-book-explores-new-world-of-digital-protest/",
        "urlToImage": "https://cdn.arstechnica.net/wp-content/uploads/2017/07/Screen-Shot-2017-07-22-at-1.17.15-PM-760x380.png",
        "publishedAt": "2017-07-23T15:00:02Z"
    }, {
        "author": "Nathan Mattise",
        "title": "Maybe The Americans is quietly a technophile love letter to the 1980s",
        "description": "Joel Fields and Joe Weisberg talk handheld football, spy tech, mail robot, and more.",
        "url": "https://arstechnica.com/the-multiverse/2017/07/maybe-the-americans-is-quietly-a-technophile-love-letter-to-the-1980s/",
        "urlToImage": "https://cdn.arstechnica.net/wp-content/uploads/2017/07/AmericansFootball-600x380.jpg",
        "publishedAt": "2017-07-23T14:30:15Z"
    }, {
        "author": "Sam Machkovech",
        "title": "Dockless bike sharing lands in Seattle—and leads us down unsavory alleyways",
        "description": "Now in Seattle: two services, 1,000 bikes, and a shoulder shrug at helmet laws.",
        "url": "https://arstechnica.com/business/2017/07/dockless-bike-sharing-lands-in-seattle-and-leads-us-down-unsavory-alleyways/",
        "urlToImage": "https://cdn.arstechnica.net/wp-content/uploads/2017/07/IMAG3645-760x380.jpg",
        "publishedAt": "2017-07-23T14:00:32Z"
    }, {
        "author": null,
        "title": "Level up: How video games evolved to solve significant scientific problems",
        "description": "Science, your chance to use all that time spent gaming for the greater good.",
        "url": "https://arstechnica.com/gaming/2017/07/level-up-how-video-games-evolved-to-solve-significant-scientific-problems/",
        "urlToImage": "https://cdn.arstechnica.net/wp-content/uploads/2017/07/GettyImages-134429675-760x380.jpg",
        "publishedAt": "2017-07-23T13:25:25Z"
    }, {
        "author": "John Timmer",
        "title": "We’ve screwed up the coasts so badly that an invasive species is a plus",
        "description": "When native species are gone, an invasive one can provide ecosystem services.",
        "url": "https://arstechnica.com/science/2017/07/weve-screwed-up-the-coasts-so-badly-that-an-invasive-species-is-a-plus/",
        "urlToImage": "https://cdn.arstechnica.net/wp-content/uploads/2017/07/Gracilaria-vermiculophylla-760x380.jpg",
        "publishedAt": "2017-07-23T12:00:53Z"
    }, {
        "author": "Megan Geuss",
        "title": "German energy company wants to build flow batteries in old natural gas caverns",
        "description": "Research for a massive redox flow battery is underway.",
        "url": "https://arstechnica.com/business/2017/07/german-energy-company-wants-to-build-flow-batteries-in-old-natural-gas-caverns/",
        "urlToImage": "https://cdn.arstechnica.net/wp-content/uploads/2017/07/20170612-b4p-english-760x380.jpg",
        "publishedAt": "2017-07-22T15:00:22Z"
    }]
}

Answer 1

您无法将 jsonObject 转换为数组，您必须有一个 jsonArray 才能执行此操作。只需添加以下行:

JsonObject jsonObject = gson.fromJson(jsonResponse, JsonObject.class);
String articlesArrayResponse = jsonObject.getAsJsonArray("articles").getAsString();

在异常发生之前。显然，您必须为此更改该行中的参数:

Collection<ArticleResponse> enums = gson.fromJson(articlesArrayResponse, collectionType);

希望对你有帮助!