无法将 Json 文件转换为 Vector 或 HashTable 或 HashMap.... org.json

Question

我已经为此花费了几天时间。我查看了来自其他有类似问题的人的一百万个不同的帖子，并尝试了很多不同的东西，但我无法将我的 json 文件读入我的程序。

这是一个学校作业。该演示适用于一个媒体库，它读取示例 music.json 文件并在 JTree 中显示曲目。我们的第一个任务是将通用媒体库转换为特定音乐库，添加 Track 和 Album 类，并在通过应用搜索​​专辑和艺术家时从 last.fm 获取搜索结果，并将结果显示在 JTree 中。

我设法创建了专辑和曲目类，读取 last.fm json 并将其转换为专辑对象。然后我将该 Album 对象重写为一个新的 album.json 文件。从那以后，我开始着手将该 json 文件读回 MusicLibrary 类，以便它可以在 JTree 中显示结果。那就是我遇到麻烦的地方。我必须进行一些转换，因为给定的 music.json 是为了按曲目进行组织（在没有专辑类之前），现在我需要它来处理新的专辑类（其中包含曲目对象的向量）。

我不能使用任何需要 maven 或下载的 jar 才能工作的工具（所以没有 GSON 等）。我只能使用 org.json 方法。讲师的原始代码将 music.json 读入 HashTable。我已经尝试将它读入其中，读入 Vector 和 HashMap。没有任何效果。我不断收到错误：

Exception reading music library album.json: JSONObject["channel"] is not a JSONObject. 或者 Exception reading music library album.json: JSONObject["album"] is not a JSONObject.

或者没有错误，但是当我尝试打印表格/地图/矢量时，它总是空的。第一个错误是当我不使用 JSONTokener 并使用它下面的注释行时。我不知道它在哪里提出了“频道”。这在我的代码中没有。无论如何，我在下面发布我的相关代码。如果您看到大量注释掉的行，那么这些都是我尝试过的不同的东西和/或一些讲师的原始代码（例如 HashTable 库）。

album.json（我将其放入格式化程序和验证程序以便更好地显示）

{
  "album": "Believe",
  "albumTracks": [
    {
      "trackInfo": "Track Name: Believe\nArtist: Cher\nRank: 1\nDuration: 241\n\n",
      "trackArtist": "Cher",
      "trackRank": "1",
      "trackDuration": "241",
      "trackTitle": "Believe"
    },
    {
      "trackInfo": "Track Name: The Power\nArtist: Cher\nRank: 2\nDuration: 236\n\n",
      "trackArtist": "Cher",
      "trackRank": "2",
      "trackDuration": "236",
      "trackTitle": "The Power"
    },
    {
      "trackInfo": "Track Name: Runaway\nArtist: Cher\nRank: 3\nDuration: 286\n\n",
      "trackArtist": "Cher",
      "trackRank": "3",
      "trackDuration": "286",
      "trackTitle": "Runaway"
    },
    {
      "trackInfo": "Track Name: All or Nothing\nArtist: Cher\nRank: 4\nDuration: 237\n\n",
      "trackArtist": "Cher",
      "trackRank": "4",
      "trackDuration": "237",
      "trackTitle": "All or Nothing"
    },
    {
      "trackInfo": "Track Name: Strong Enough\nArtist: Cher\nRank: 5\nDuration: 223\n\n",
      "trackArtist": "Cher",
      "trackRank": "5",
      "trackDuration": "223",
      "trackTitle": "Strong Enough"
    },
    {
      "trackInfo": "Track Name: Dov'e L'amore\nArtist: Cher\nRank: 6\nDuration: 258\n\n",
      "trackArtist": "Cher",
      "trackRank": "6",
      "trackDuration": "258",
      "trackTitle": "Dov'e L'amore"
    },
    {
      "trackInfo": "Track Name: Takin' Back My Heart\nArtist: Cher\nRank: 7\nDuration: 272\n\n",
      "trackArtist": "Cher",
      "trackRank": "7",
      "trackDuration": "272",
      "trackTitle": "Takin' Back My Heart"
    },
    {
      "trackInfo": "Track Name: Taxi Taxi\nArtist: Cher\nRank: 8\nDuration: 304\n\n",
      "trackArtist": "Cher",
      "trackRank": "8",
      "trackDuration": "304",
      "trackTitle": "Taxi Taxi"
    },
    {
      "trackInfo": "Track Name: Love Is the Groove\nArtist: Cher\nRank: 9\nDuration: 271\n\n",
      "trackArtist": "Cher",
      "trackRank": "9",
      "trackDuration": "271",
      "trackTitle": "Love Is the Groove"
    },
    {
      "trackInfo": "Track Name: We All Sleep Alone\nArtist: Cher\nRank: 10\nDuration: 233\n\n",
      "trackArtist": "Cher",
      "trackRank": "10",
      "trackDuration": "233",
      "trackTitle": "We All Sleep Alone"
    }
  ],
  "albumArtist": "Cher",
  "albumSummary": "Believe is the twenty-third studio album by American  singer-actress Cher, released on November 10, 1998 by Warner Bros. Records. The RIAA certified it Quadruple Platinum on December 23, 1999, recognizing four million shipments in the United States; Worldwide, the album has sold more than 20 million copies, making it the biggest-selling album of her career. In 1999 the album received three Grammy Awards nominations including \"Record of the Year\", \"Best Pop Album\" and winning \"Best Dance Recording\" for the single \"Believe\". <a href=\"http://www.last.fm/music/Cher/Believe\">Read more on Last.fm</a>.",
  "albumImage": "https://lastfm.freetls.fastly.net/i/u/174s/b0c2311a9af7f0edbc8b99450944ca1b.png"
}

我的 Album.java 类，因此您可以看到我如何将 Album 对象写入 Json，以防出现问题。

    /**
     * Converts the Album object along with its associated Track objects to a JSONObject toString
     * 
     * @return Returns the Album/Track objects as a JSONObject toString
     */
    public String toJString() {
        String jString = "{}";
        try {
            jString = this.albumToJObject().toString(0);
        } catch (Exception ex) {
            System.out.println("Exception in Album toJString: " + ex.getMessage());
        }
        return jString;
    }

    /**
     * Converts the Track object to a JSONObject.
     * 
     * @return Returns the Track object as a JSONObject.
     */
    public JSONObject albumToJObject() {
        JSONObject jObject = new JSONObject();
        try {
            jObject.put("album", albumName);
            jObject.put("albumArtist", albumArtist);
            jObject.put("albumImage", albumImage);
            jObject.put("albumSummary", albumSummary);
            jObject.put("albumTracks", (Object)albumTracks);

            // System.out.println("Full Album JSONObject: " + jObject.toString());

        } catch (Exception ex) {
            System.out.println("Exception in Album toJObject: " + ex.getMessage());
        }
        return jObject;
    }

    public void writeAlbumToJson() {
        try {
            Writer output = null;
            File file = new File("album.json");
            output = new BufferedWriter(new FileWriter(file));
            output.write(this.albumToJObject().toString());
            output.close();
        } catch (Exception ex) {
            ex.printStackTrace();
            System.out.println("Exception in writeAlbumToJson: " + ex.getMessage());
        }
    }

这是 MusicLibrary 类声明和构造函数，为了清楚我当前的代码是什么而进行了清理：

public class MusicLibrary extends Object implements Serializable {

    private Map<String, Album> musicLib;
    private static final String mFileName = "album.json";

    public MusicLibrary() {
        this.musicLib = new HashMap<String, Album>();
        try {
            InputStream inputStream = this.getClass().getClassLoader().getResourceAsStream(this.mFileName);
            if (inputStream == null) {
                inputStream = new FileInputStream(new File(this.mFileName));
            }
            JSONObject music = new JSONObject(new JSONTokener(inputStream));
            Iterator<String> iter = music.keys();

            while(iter.hasNext()) {
                String key = iter.next();
                JSONObject jAlbumObj = music.optJSONObject(key);
                if (music.get(key) instanceof JSONObject) {
                    Album album = new Album(jAlbumObj);
                    musicLib.put(key, album);      
                }
            }

            System.out.println("DEBUG: musicLib HashMap contents: " + musicLib.toString());
        } catch (Exception ex) {
            ex.printStackTrace();
            System.out.println("Exception reading music library " + mFileName + ": " + ex.getMessage());
        }
    }

Answer 1

根据您的解释，我了解到MusicLibrary 应该读取album.json 文件并将其转换为地图Map<String, Album> musicLib;，其中关键是专辑名称。

您没有提供整个 Album 和 Track 类，但我会假设它们具有接受 JSONObject 参数的构造函数。

您的错误是您尝试遍历JSONObject。 iter.next() 将始终只返回 Object，而不是您想要的 JSONObject。另外，考虑到您提供的album.json 只有一张专辑，根本没有必要进行迭代（除非album.json 应该有多个专辑）。

另外，我认为 json 结构（键名）是已知的，因此您可以使用这些名称来提取数据。请看下面的代码：

public class MusicLibrary{

    private Map<String, Album> musicLib;
    private static final String mFileName = "album.json";

    public MusicLibrary() {
        this.musicLib = new HashMap<>();
        try {
            InputStream inputStream = getClass().getClassLoader().getResourceAsStream(this.mFileName);
            if (inputStream == null) {
                inputStream = new FileInputStream(new File(this.mFileName));
            }

            JSONObject jAlbum = new JSONObject(new JSONTokener(inputStream));
            Album album = new Album(jAlbum);
            musicLib.put(album.getAlbumName(), album);

            System.out.println("DEBUG: musicLib HashMap contents: " + musicLib.toString());
        } catch (Exception ex) {
            ex.printStackTrace();
            System.out.println("Exception reading music library " + mFileName + ": " + ex.getMessage());
        }
    }


}

public class Album {

    private String albumName;
    private String albumArtist;
    private String albumImage;
    private String albumSummary;
    private List<Track> albumTracks = new LinkedList<>();

    public Album(JSONObject obj) {
        albumName = obj.getString("album");
        albumArtist = obj.getString("albumArtist");
        albumImage = obj.getString("albumImage");
        albumSummary = obj.getString("albumSummary");
        JSONArray tracks = obj.getJSONArray("albumTracks");

        for (int i = 0; i < tracks.length(); i++) {
            albumTracks.add(new Track(tracks.getJSONObject(i)));
        }
    }

    public String getAlbumName() {
        return albumName;
    }


    @Override
    public String toString() {
        return "Album{" +
                "albumName='" + albumName + '\'' +
                ", albumArtist='" + albumArtist + '\'' +
                ", albumImage='" + albumImage + '\'' +
                ", albumSummary='" + albumSummary + '\'' +
                ", albumTracks=" + albumTracks +
                '}';
    }
}

public class Track {
    private String trackInfo;
    private String trackArtist;
    private String trackRank;
    private String trackDuration;
    private String trackTitle;

    public Track(JSONObject obj) {
        trackInfo = obj.getString("trackInfo");
        trackArtist = obj.getString("trackArtist");
        trackRank = obj.getString("trackRank");
        trackDuration = obj.getString("trackDuration");
        trackTitle = obj.getString("trackTitle");
    }
    @Override
    public String toString() {
        return "Track{" +
                "trackInfo='" + trackInfo + '\'' +
                ", trackArtist='" + trackArtist + '\'' +
                ", trackRank='" + trackRank + '\'' +
                ", trackDuration='" + trackDuration + '\'' +
                ", trackTitle='" + trackTitle + '\'' +
                '}';
    }
}

最后，考虑从MusicLibrary 构造函数中删除逻辑和文件读取，不要显式扩展Object，也不要实现Serializable，除非你真的知道自己在做什么。