Question

我创建了一个使用Google Books API的Android应用程序。当我从服务器获得JSON响应时，我解析响应并检索标题，作者，类别，发布者，页数，缩略图以及有关该书的更多信息。问题是JSON响应中的某些书籍没有缩略图键或类别键。当我尝试获取这些JSON键值时，程序会抛出错误，因此在发生错误后会跳过添加其他书籍的代码。

我用嵌套尝试了catch块解决了这个问题。例如，如果响应中没有发布者密钥，那么我将返回null。

String publisher;
  try {
    publisher = volumeInfo.getString("publisher");
  } catch (JSONException e) {
    publisher = null;
  }

以下是解析JSON响应的整个方法如下所示：

private List<BookData> parseJsonResponse(String jsonResponse) {
    List<BookData> bookData = new ArrayList<>();

    try {
        JSONObject rootObject = new JSONObject(jsonResponse);
        JSONArray itemsArray = rootObject.getJSONArray("items");
        for (int i = 0; i < itemsArray.length(); i++) {
            JSONObject itemObject = itemsArray.getJSONObject(i);
            JSONObject volumeInfo = 
              itemObject.getJSONObject("volumeInfo");

            String title;
            try {
                title = volumeInfo.getString("title");
            } catch (JSONException e) {
                title = null;
            }

            ArrayList<String> authors;
            try {
                JSONArray authorsArray = 
                  volumeInfo.getJSONArray("authors");
                authors = new ArrayList<>();
                for (int j = 0; j < authorsArray.length(); j++) {
                    authors.add(authorsArray.getString(j));
                }
            } catch (JSONException e) {
                authors = null;
            }

            ArrayList<String> categories;
            try {
                JSONArray categoriesArray = 
                  volumeInfo.getJSONArray("categories");
                categories = new ArrayList<>();
                for (int k = 0; k < categoriesArray.length(); k++) {
                    categories.add(categoriesArray.getString(k));
                }
            } catch (JSONException e) {
                categories = null;
            }

            String publisher;
            try {
                publisher = volumeInfo.getString("publisher");
            } catch (JSONException e) {
                publisher = null;
            }

            String publishedDate;
            try {
                publishedDate = 
                  volumeInfo.getString("publishedDate");
            } catch (JSONException e) {
                publishedDate = null;
            }

            int pageCount;
            try {
                pageCount = volumeInfo.getInt("pageCount");
            } catch (JSONException e) {
                pageCount = 0;
            }

            String language;
            try {
                language = volumeInfo.getString("language");
            } catch (JSONException e) {
                language = null;
            }

            String description;
            try {
                description = volumeInfo.getString("description");
            } catch (JSONException e) {
                description = null;
            }

            String bookWebsite;
            try {
                bookWebsite = volumeInfo.getString("infoLink");
            } catch (JSONException e) {
                bookWebsite = null;
            }

            Bitmap thumbnail;
            try {
                JSONObject imageLink = 
                  volumeInfo.getJSONObject("imageLinks");
                String thumbnailUrl = 
                  imageLink.getString("thumbnail");
                thumbnail = getThumbnailBitmap(thumbnailUrl);
            } catch (JSONException e) {
                thumbnail = null;
            }

            // Add a new BookData object to the list
            bookData.add(new BookData(title, thumbnail, authors, 
                       categories, publisher, publishedDate, 
                       pageCount, language, description,
                       bookWebsite));
        }
    } catch (JSONException e) {
        Log.e(LOG_TAG, null, e);
    }
    return bookData;
}

完成解析后，我必须更新我的观点。我正在使用列表视图，因此适配器需要处理视图通胀。我必须添加一个if语句来检查变量是否为null，然后例如设置文本视图的文本。另外，我将文本设置为＆＃34;发布者不可用＆＃34;。

TextView publisher = listView.findViewById(R.id.book_publisher);
  if (bookData.getPublisher() != null) {
    publisher.setText(bookData.getPublisher());
    } else {
    publisher.setText("Publisher not available");
    }

以下是整个适配器的外观：

public class BookDataAdapter extends ArrayAdapter<BookData> {

public BookDataAdapter(@NonNull Context context, @NonNull 
                        List<BookData> bookDatas) {
    super(context, 0, bookDatas);
}

@NonNull
@Override
public View getView(int position, @Nullable View convertView, 
                     @NonNull ViewGroup parent) {
    View listView = convertView;
    if (listView == null) {
        listView = LayoutInflater.from(getContext())
                .inflate(R.layout.book_list_item, parent, false);
    }
    // Get current BookData object
    BookData bookData = getItem(position);

    ImageView thumbnail = listView.findViewById(R.id.book_thumbnail);
    if (bookData.getThumbnail() != null) {
        thumbnail.setImageBitmap(bookData.getThumbnail());
    } else {
        // Set default thumbnail
        thumbnail.setImageResource(R.drawable.default_thumbnail);
    }

    TextView title = listView.findViewById(R.id.book_title);
    if (bookData.getTitle() != null) {
        title.setText(bookData.getTitle());
    } else {
        title.setText("Title not available");
    }

    TextView author = listView.findViewById(R.id.book_author);
    if (bookData.getAuthors() != null) {
        author.setText(listToString(bookData.getAuthors()));
    } else {
        author.setText("Authors not available");
    }

    TextView category = listView.findViewById(R.id.book_category);
    if (bookData.getCategories() != null) {
        category.setText("Category: " + 
      listToString(bookData.getCategories()));
    } else {
        category.setText("Category not available ");
    }

    TextView publisher = listView.findViewById(R.id.book_publisher);
    if (bookData.getPublisher() != null) {
        publisher.setText(bookData.getPublisher() + ", ");
    } else {
        publisher.setText("Publisher not available, ");
    }

    TextView publishedDate = 
      listView.findViewById(R.id.book_published_date);
    if (bookData.getPublishedDate() != null) {
        publishedDate.setText(bookData.getPublishedDate());
    } else {
        publishedDate.setText("Published date not available");
    }

    TextView pageCount = listView.findViewById(R.id.book_page_count);
    if (bookData.getPageCount() != 0) {
        pageCount.setText("Pages: " + bookData.getPageCount());
    } else {
        pageCount.setText("Page count not available");
    }

    TextView language = listView.findViewById(R.id.book_language);
    if (bookData.getLanguage() != null) {
        language.setText(bookData.getLanguage());
    } else {
        language.setText("Language not available");
    }

    TextView description = 
      listView.findViewById(R.id.book_description);
    if (bookData.getDescription() != null) {
        description.setText(bookData.getDescription());
    } else {
        description.setText("Description not available");
    }
    return listView;
}

private String listToString(List<String> list) {
    if (list == null || list.size() == 0) {
        return null;
    }
    StringBuilder builder = new StringBuilder();
    for (int i = 0; i < list.size(); i++) {
        builder.append(list.get(i));
        if (i == (list.size() - 1)) {
            break;
        }
        builder.append(", ");
    }
    return builder.toString();
}

}

最后我想问一个问题。是否有更好的方法或更有效的方法使用不同的密钥解析JSON响应，因为有些人说嵌套的try catch语句不是一个好的做法？

非常感谢!!

Answer 1

您有两种选择：

使用.has()：

String publisher = null;
if(volumeInfo.has("publisher")){
    publisher = volumeInfo.getString("publisher");
}

使用opt代替get（更好，IMO）：

String publisher = volumeInfo.optString("publisher");

opt###方法对于对象默认为null，对于基元默认为0 / false，因此您不必编写try/catch块或if条件。您还可以将第二个参数指定为默认值：

String publisher = volumeInfo.optString("publisher", "no publisher");
// if publisher is not a valid key, "no publisher" will be returned

Answer 2

使用.has()

的JSONObject属性

if(volumeInfo.has("publisher")){
   volumeInfo.getString("publisher");
}

Answer 3

您不需要在单独的try / catch块中包装json操作。

json库中有一个方法可以解决这个问题：

jsonObject.isNull(key);

当您尝试按键获取值时，请按以下方式写入：

if (!volumeInfo.isNull("categories")) {
    JSONArray categoryArray = volumeInfo.getJSONArray("categories");
}

使用不同的密钥解析JSON对象

3 个答案: