java - 检查 jsonArray 是否为 null

Question

我正在尝试检查 json 数组以获取作者姓名，如果为 null，我需要给我未知作者这个 json 数组

{  
   "kind":"books#volumes",
   "totalItems":604,
   "items":[  
      {  
         "kind":"books#volume",
         "id":"6tLAyQLSzG0C",
         "etag":"wtUTTM0nDQA",
         "selfLink":"https://www.googleapis.com/books/v1/volumes/6tLAyQLSzG0C",
         "volumeInfo":{  
            "title":"Android for Work",
            "subtitle":"Productivity for Professionals",
            "authors":[  
               "Marziah Karch"
            ],

这是我的java代码

 // Create a JSONObject from the JSON response string
        JSONObject root = new JSONObject(bookJSON);

        // Extract the JSONArray
        // which represents list of title of book ant author name.
        JSONArray bookArray = root.getJSONArray("items");

        for (int i = 0; i < bookArray.length(); i++) {

            // Get a single booka t position i within the list of books
            JSONObject currentBook = bookArray.getJSONObject(i);
            JSONObject volumeInfo = currentBook.getJSONObject("volumeInfo");
            // Extract the value for the key called " title"
            String title="";
            if(volumeInfo.has("title"))
            { title = volumeInfo.getString("title");}
            JSONArray authors= volumeInfo.getJSONArray("authors");
            String author = "";


                for (int j = 0; j < authors.length(); j++) {
                    if(authors.length()==0){
                // Convert the authors to a string
                author = authors.getString(j);}else{author="unknown";}}

我可以获得书名，但作者姓名始终未知，我不知道为什么？

Answer 1

您的问题是在这种情况下if(authors.length()==0)

这应该是:

JSONArray authors= volumeInfo.getJSONArray("authors");
String author = null;
if(authors.length() > 0) {
    author = authors.getString(authors.length() - 1);
} else {
    author="unknown";
}