java - JSONException : No value for book_details

Question

我正在尝试从此网址中抓取书名:http://api.nytimes.com/svc/books/v2/lists/2010-10-01/trade-fiction-paperback?api-key=c775dd98c5a108e9ebc790ca2c47ac19:18:74338855

我使用以下代码从该网址中抓取信息，该代码当时有效:http://api.openweathermap.org/data/2.5/weather?q=London,uk&appid=44db6a862fba0b067b1930da0d769e98

它适用于第二个网址，因为我只抓取了一个“天气”字符串。然而，在另一个网址中有几个“book_details”字符串，我不知道如何从每个字符串中抓取标题。

这是我的代码，返回 JSONException: No value for book_details。

public class MainActivity extends AppCompatActivity {

public class DownloadTask extends AsyncTask<String, Void, String>{

    @Override
    protected String doInBackground(String... urls) {

        String result = "";
        URL url;
        HttpURLConnection urlConnection = null;

        try {

            url = new URL(urls[0]);

            urlConnection = (HttpURLConnection)url.openConnection();

            InputStream in = urlConnection.getInputStream();

            InputStreamReader reader = new InputStreamReader(in);

            int data = reader.read();

            while (data != -1){

                char current = (char) data;

                result += current;

                data = reader.read();

            }

            return result;

        } catch (MalformedURLException e) {

            e.printStackTrace();

        } catch (IOException e) {

            e.printStackTrace();

        }

        return null;

    }

    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);

        try {

            JSONObject jsonObject = new JSONObject(result);

            String bookInfo = jsonObject.getString("book_details");

            Log.i("Book Info", bookInfo);


        } catch (JSONException e) {

            e.printStackTrace();

        }


    }
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    DownloadTask task = new DownloadTask();
    task.execute("http://api.openweathermap.org/data/2.5/weather?q=London,uk&appid=44db6a862fba0b067b1930da0d769e98");

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}
}

我认为问题出在 onPostExecute 方法中。任何帮助将不胜感激。

Answer 1

您的代码的一个大问题是您没有正确循环结果。您收到的是每本书的 JSONObjects JSONArray，因此您需要正确循环每个数组。下面是一个基本示例，说明了提取名称和描述。从那里您确实可以获取任何您想要的信息。不过，我强烈建议学习如何在 Android 中解析 JSONObjects 和数组。

 try {

            JSONObject jsonObject = new JSONObject(result);
            JSONArray jsonArray = jsonObject.getJSONArray("results");

            for(int i = 0; i < jsonArray.length(); i++) {
                JSONObject currentObject = jsonArray.getJSONObject(i);
                JSONArray currentArray = currentObject.getJSONArray("book_details");
                for(int x = 0; x < currentArray.length(); x++){
                    JSONObject book = currentArray.getJSONObject(x);
                    String bookTitle = book.getString("title");
                    String bookDescription = book.getString("description");
                    Log.i("Book Title: ", bookTitle);
                    Log.i("Book Description: ", bookDescription);
                }
            }
 }catch(JSONException e){
     e.printStackTrace();
 }

输出

其他资源

http://developer.android.com/reference/org/json/JSONObject.html

http://www.tutorialspoint.com/android/android_json_parser.htm

http://www.vogella.com/tutorials/AndroidJSON/article.html