java JSON异常在Android中没有值

Question

我在日志中收到这个错误消息，我被困在这里了。我正在使用Gson解析JSON数据。这是我的主要活动和模型课

我研究了针对同一JSON异常发布的其他问题，但找不到解决方案，所以我为我的项目发布了这个问题

另外，请告知我是否使用正确的方法在textview中显示数据

主要活动

public class MainActivity extends AppCompatActivity {

public static final String Logcat = "vmech";

Button searchButton;
EditText editTextSearch;
TextView textViewDisplayResult;
String newText;
String urlstring;

public static final String MyAPIKey =  "Your_Api_Key";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    searchButton = (Button) findViewById(R.id.buttonSerch);
    editTextSearch = (EditText) findViewById(R.id.editTextSearch);
    textViewDisplayResult = (TextView) findViewById(R.id.textViewDisplayResult);

    searchButton.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v) {
            newText = editTextSearch.getText().toString();
            if(newText.length()>0){
                newText = newText.replace(" ", "+");
                urlstring = "https://www.googleapis.com/books/v1/volumes?q=";
                urlstring = urlstring + newText + "&maxResults=5" + "&key=" + MyAPIKey;

            }
            else {
                Toast.makeText(MainActivity.this, "Please enter a book name to search.", Toast.LENGTH_LONG).show();

            }
            new JSONTask().execute(urlstring);

        }
    });
}

@Override
public boolean onCreateOptionsMenu(Menu menu)
{

    MenuInflater inflater=getMenuInflater();
    inflater.inflate(R.menu.menu_main, menu);
    return true;

}

@Override
public boolean onOptionsItemSelected(MenuItem item)
{
    Toast.makeText(this, "This is the Settings item", Toast.LENGTH_LONG).show();
    return true;

}

public class JSONTask extends AsyncTask<String, String, List<BookInfoModel>>{

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    @Override
    protected List<BookInfoModel> doInBackground(String... params) {
        HttpURLConnection connection = null;
        BufferedReader bufferedReader = null;

        try {
            URL url = new URL(urlstring);

            connection = (HttpURLConnection) url.openConnection();
            connection.connect();

            InputStream inputstream = connection.getInputStream();
            bufferedReader = new BufferedReader(new InputStreamReader(inputstream));

            StringBuffer stringbuffer = new StringBuffer();

            String line = "";
            while ((line = bufferedReader.readLine()) != null) {
                stringbuffer.append(line);
            }

            String finalJson = stringbuffer.toString();

            JSONObject parentObject = new JSONObject(finalJson);
            JSONArray parentArray = parentObject.getJSONArray("items");

            List<BookInfoModel> bookInfoModelList = new ArrayList<>();
            String idText = null;
            Gson gson = new Gson();
            for(int i=0; i<parentArray.length(); i++){
                JSONObject finalObject = parentArray.getJSONObject(i);

                BookInfoModel bookInfoModel = gson.fromJson(finalObject.toString(),BookInfoModel.class);

                bookInfoModelList.add(bookInfoModel);
            }


            return bookInfoModelList;

        } catch (IOException e){
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        } finally {
            if (connection != null)
            {
                connection.disconnect();
            }
            try {
                if (bufferedReader != null){
                    bufferedReader.close();
                }
            }catch (IOException e){
                e.printStackTrace();
            }
        }

        return null;

    }

    @Override
    protected void onPostExecute(List<BookInfoModel> result) {
        super.onPostExecute(result);
        textViewDisplayResult.setText((CharSequence) result);
    }
}

}

这是我的JSON数据模型类

import com.google.gson.annotations.SerializedName;

import java.util.List;

public class BookInfoModel {
private List<Items> items;

private String totalItems;

private String kind;

public List<Items> getItems() {
    return items;
}

public void setItems(List<Items> items) {
    this.items = items;
}

public String getTotalItems ()
{
    return totalItems;
}

public void setTotalItems (String totalItems)
{
    this.totalItems = totalItems;
}

public String getKind ()
{
    return kind;
}

public void setKind (String kind)
{
    this.kind = kind;
}


public class Items
{
    private SaleInfo saleInfo;

    private String id;

    private SearchInfo searchInfo;

    private String etag;

    private List<VolumeInfo> volumeInfo;

    private String selfLink;

    private AccessInfo accessInfo;

    private String kind;

    public SaleInfo getSaleInfo ()
    {
        return saleInfo;
    }

    public void setSaleInfo (SaleInfo saleInfo)
    {
        this.saleInfo = saleInfo;
    }

    public String getId ()
    {
        return id;
    }

    public void setId (String id)
    {
        this.id = id;
    }

    public SearchInfo getSearchInfo ()
    {
        return searchInfo;
    }

    public void setSearchInfo (SearchInfo searchInfo)
    {
        this.searchInfo = searchInfo;
    }

    public String getEtag ()
    {
        return etag;
    }

    public void setEtag (String etag)
    {
        this.etag = etag;
    }

    public List<VolumeInfo> getVolumeInfo() {
        return volumeInfo;
    }

    public void setVolumeInfo(List<VolumeInfo> volumeInfo) {
        this.volumeInfo = volumeInfo;
    }

    public String getSelfLink ()
    {
        return selfLink;
    }

    public void setSelfLink (String selfLink)
    {
        this.selfLink = selfLink;
    }

    public AccessInfo getAccessInfo ()
    {
        return accessInfo;
    }

    public void setAccessInfo (AccessInfo accessInfo)
    {
        this.accessInfo = accessInfo;
    }

    public String getKind ()
    {
        return kind;
    }

    public void setKind (String kind)
    {
        this.kind = kind;
    }

    public class SearchInfo
    {
        private String textSnippet;

        public String getTextSnippet ()
        {
            return textSnippet;
        }

        public void setTextSnippet (String textSnippet)
        {
            this.textSnippet = textSnippet;
        }
    }

    public class AccessInfo
    {
        private String webReaderLink;

        private String textToSpeechPermission;

        private String publicDomain;

        private String viewability;

        private String accessViewStatus;

        private Pdf pdf;

        private Epub epub;

        private String embeddable;

        private String quoteSharingAllowed;

        private String country;

        public String getWebReaderLink ()
        {
            return webReaderLink;
        }

        public void setWebReaderLink (String webReaderLink)
        {
            this.webReaderLink = webReaderLink;
        }

        public String getTextToSpeechPermission ()
        {
            return textToSpeechPermission;
        }

        public void setTextToSpeechPermission (String textToSpeechPermission)
        {
            this.textToSpeechPermission = textToSpeechPermission;
        }

        public String getPublicDomain ()
        {
            return publicDomain;
        }

        public void setPublicDomain (String publicDomain)
        {
            this.publicDomain = publicDomain;
        }

        public String getViewability ()
        {
            return viewability;
        }

        public void setViewability (String viewability)
        {
            this.viewability = viewability;
        }

        public String getAccessViewStatus ()
        {
            return accessViewStatus;
        }

        public void setAccessViewStatus (String accessViewStatus)
        {
            this.accessViewStatus = accessViewStatus;
        }

        public Pdf getPdf ()
        {
            return pdf;
        }

        public void setPdf (Pdf pdf)
        {
            this.pdf = pdf;
        }

        public Epub getEpub ()
        {
            return epub;
        }

        public void setEpub (Epub epub)
        {
            this.epub = epub;
        }

        public String getEmbeddable ()
        {
            return embeddable;
        }

        public void setEmbeddable (String embeddable)
        {
            this.embeddable = embeddable;
        }

        public String getQuoteSharingAllowed ()
        {
            return quoteSharingAllowed;
        }

        public void setQuoteSharingAllowed (String quoteSharingAllowed)
        {
            this.quoteSharingAllowed = quoteSharingAllowed;
        }

        public String getCountry ()
        {
            return country;
        }

        public void setCountry (String country)
        {
            this.country = country;
        }

        public class Pdf
        {
            private String acsTokenLink;

            private String isAvailable;

            public String getAcsTokenLink ()
            {
                return acsTokenLink;
            }

            public void setAcsTokenLink (String acsTokenLink)
            {
                this.acsTokenLink = acsTokenLink;
            }

            public String getIsAvailable ()
            {
                return isAvailable;
            }

            public void setIsAvailable (String isAvailable)
            {
                this.isAvailable = isAvailable;
            }
        }

        public class Epub
        {
            private String acsTokenLink;

            private String isAvailable;

            public String getAcsTokenLink ()
            {
                return acsTokenLink;
            }

            public void setAcsTokenLink (String acsTokenLink)
            {
                this.acsTokenLink = acsTokenLink;
            }

            public String getIsAvailable ()
            {
                return isAvailable;
            }

            public void setIsAvailable (String isAvailable)
            {
                this.isAvailable = isAvailable;
            }
        }
    }

    public class SaleInfo
    {
        private RetailPrice retailPrice;

        private String saleability;

        private ListPrice listPrice;

        private Offers[] offers;

        private String buyLink;

        private String isEbook;

        private String country;

        public RetailPrice getRetailPrice ()
        {
            return retailPrice;
        }

        public void setRetailPrice (RetailPrice retailPrice)
        {
            this.retailPrice = retailPrice;
        }

        public String getSaleability ()
        {
            return saleability;
        }

        public void setSaleability (String saleability)
        {
            this.saleability = saleability;
        }

        public ListPrice getListPrice ()
        {
            return listPrice;
        }

        public void setListPrice (ListPrice listPrice)
        {
            this.listPrice = listPrice;
        }

        public Offers[] getOffers ()
        {
            return offers;
        }

        public void setOffers (Offers[] offers)
        {
            this.offers = offers;
        }

        public String getBuyLink ()
        {
            return buyLink;
        }

        public void setBuyLink (String buyLink)
        {
            this.buyLink = buyLink;
        }

        public String getIsEbook ()
        {
            return isEbook;
        }

        public void setIsEbook (String isEbook)
        {
            this.isEbook = isEbook;
        }

        public String getCountry ()
        {
            return country;
        }

        public void setCountry (String country)
        {
            this.country = country;
        }

        public class Offers
        {
            private RetailPrice retailPrice;

            private ListPrice listPrice;

            private String finskyOfferType;

            public RetailPrice getRetailPrice ()
            {
                return retailPrice;
            }

            public void setRetailPrice (RetailPrice retailPrice)
            {
                this.retailPrice = retailPrice;
            }

            public ListPrice getListPrice ()
            {
                return listPrice;
            }

            public void setListPrice (ListPrice listPrice)
            {
                this.listPrice = listPrice;
            }

            public String getFinskyOfferType ()
            {
                return finskyOfferType;
            }

            public void setFinskyOfferType (String finskyOfferType)
            {
                this.finskyOfferType = finskyOfferType;
            }
        }

        public class RetailPrice
        {
            private String amount;

            private String currencyCode;

            public String getAmount ()
            {
                return amount;
            }

            public void setAmount (String amount)
            {
                this.amount = amount;
            }

            public String getCurrencyCode ()
            {
                return currencyCode;
            }

            public void setCurrencyCode (String currencyCode)
            {
                this.currencyCode = currencyCode;
            }
        }

        public class ListPrice
        {
            private String amount;

            private String currencyCode;

            public String getAmount ()
            {
                return amount;
            }

            public void setAmount (String amount)
            {
                this.amount = amount;
            }

            public String getCurrencyCode ()
            {
                return currencyCode;
            }

            public void setCurrencyCode (String currencyCode)
            {
                this.currencyCode = currencyCode;
            }
        }
    }

    public class VolumeInfo
    {
        private String pageCount;

        private String averageRating;

        private ReadingModes readingModes;

        private String infoLink;

        private String printType;

        private String allowAnonLogging;

        private String publisher;

        private String[] authors;

        private String canonicalVolumeLink;

        @SerializedName("title")
        private String title;

        private String previewLink;

        private String description;

        private String ratingsCount;

        private ImageLinks imageLinks;

        private String contentVersion;

        private String[] categories;

        private String language;

        private String publishedDate;

        private IndustryIdentifiers[] industryIdentifiers;

        private String maturityRating;

        public String getPageCount ()
        {
            return pageCount;
        }

        public void setPageCount (String pageCount)
        {
            this.pageCount = pageCount;
        }

        public String getAverageRating ()
        {
            return averageRating;
        }

        public void setAverageRating (String averageRating)
        {
            this.averageRating = averageRating;
        }

        public ReadingModes getReadingModes ()
        {
            return readingModes;
        }

        public void setReadingModes (ReadingModes readingModes)
        {
            this.readingModes = readingModes;
        }

        public String getInfoLink ()
        {
            return infoLink;
        }

        public void setInfoLink (String infoLink)
        {
            this.infoLink = infoLink;
        }

        public String getPrintType ()
        {
            return printType;
        }

        public void setPrintType (String printType)
        {
            this.printType = printType;
        }

        public String getAllowAnonLogging ()
        {
            return allowAnonLogging;
        }

        public void setAllowAnonLogging (String allowAnonLogging)
        {
            this.allowAnonLogging = allowAnonLogging;
        }

        public String getPublisher ()
        {
            return publisher;
        }

        public void setPublisher (String publisher)
        {
            this.publisher = publisher;
        }

        public String[] getAuthors ()
        {
            return authors;
        }

        public void setAuthors (String[] authors)
        {
            this.authors = authors;
        }

        public String getCanonicalVolumeLink ()
        {
            return canonicalVolumeLink;
        }

        public void setCanonicalVolumeLink (String canonicalVolumeLink)
        {
            this.canonicalVolumeLink = canonicalVolumeLink;
        }

        public String getTitle ()
        {
            return title;
        }

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

        public String getPreviewLink ()
        {
            return previewLink;
        }

        public void setPreviewLink (String previewLink)
        {
            this.previewLink = previewLink;
        }

        public String getDescription ()
        {
            return description;
        }

        public void setDescription (String description)
        {
            this.description = description;
        }

        public String getRatingsCount ()
        {
            return ratingsCount;
        }

        public void setRatingsCount (String ratingsCount)
        {
            this.ratingsCount = ratingsCount;
        }

        public ImageLinks getImageLinks ()
        {
            return imageLinks;
        }

        public void setImageLinks (ImageLinks imageLinks)
        {
            this.imageLinks = imageLinks;
        }

        public String getContentVersion ()
        {
            return contentVersion;
        }

        public void setContentVersion (String contentVersion)
        {
            this.contentVersion = contentVersion;
        }

        public String[] getCategories ()
        {
            return categories;
        }

        public void setCategories (String[] categories)
        {
            this.categories = categories;
        }

        public String getLanguage ()
        {
            return language;
        }

        public void setLanguage (String language)
        {
            this.language = language;
        }

        public String getPublishedDate ()
        {
            return publishedDate;
        }

        public void setPublishedDate (String publishedDate)
        {
            this.publishedDate = publishedDate;
        }

        public IndustryIdentifiers[] getIndustryIdentifiers ()
        {
            return industryIdentifiers;
        }

        public void setIndustryIdentifiers (IndustryIdentifiers[] industryIdentifiers)
        {
            this.industryIdentifiers = industryIdentifiers;
        }

        public String getMaturityRating ()
        {
            return maturityRating;
        }

        public void setMaturityRating (String maturityRating)
        {
            this.maturityRating = maturityRating;
        }

        public class ImageLinks
        {
            private String thumbnail;

            private String smallThumbnail;

            public String getThumbnail ()
            {
                return thumbnail;
            }

            public void setThumbnail (String thumbnail)
            {
                this.thumbnail = thumbnail;
            }

            public String getSmallThumbnail ()
            {
                return smallThumbnail;
            }

            public void setSmallThumbnail (String smallThumbnail)
            {
                this.smallThumbnail = smallThumbnail;
            }
        }

        public class ReadingModes
        {
            private String text;

            private String image;

            public String getText ()
            {
                return text;
            }

            public void setText (String text)
            {
                this.text = text;
            }

            public String getImage ()
            {
                return image;
            }

            public void setImage (String image)
            {
                this.image = image;
            }
        }

        public class IndustryIdentifiers
        {
            private String type;

            private String identifier;

            public String getType ()
            {
                return type;
            }

            public void setType (String type)
            {
                this.type = type;
            }

            public String getIdentifier ()
            {
                return identifier;
            }

            public void setIdentifier (String identifier)
            {
                this.identifier = identifier;
            }
        }
    }
}

}

下面是我试图解析的JSON数据

{

"kind": "books#volumes",
"totalItems": 1557,
"items": [
    {
        "kind": "books#volume",
        "id": "An4_e3Cr3zAC",
        "etag": "DWmqBRkB8dw",
        "selfLink": "https://www.googleapis.com/books/v1/volumes/An4_e3Cr3zAC",
        "volumeInfo": {
            "title": "The Rules of the Game",
            "authors": [
                "Neil Strauss"
            ],
            "publisher": "Canongate Books",
            "publishedDate": "2011-09-29",
            "description": "If you want to play The Game you need to know The Rules This book is not a story.",
            "industryIdentifiers": [
                {
                    "type": "ISBN_13",
                    "identifier": "9781847673558"
                },
                {
                    "type": "ISBN_10",
                    "identifier": "1847673554"
                }
            ],
            "readingModes": {
                "text": true,
                "image": true
            },
            "pageCount": 352,
            "printType": "BOOK",
            "categories": [
                "Biography & Autobiography"
            ],
            "averageRating": 3.5,
            "ratingsCount": 82,
            "maturityRating": "NOT_MATURE",
            "allowAnonLogging": true,
            "contentVersion": "1.7.6.0.preview.3",
            "imageLinks": {
                "smallThumbnail": "http://books.google.co.in/books/content?id=An4_e3Cr3zAC&printsec=frontcover&img=1&zoom=5&edge=curl&source=gbs_api",
                "thumbnail": "http://books.google.co.in/books/content?id=An4_e3Cr3zAC&printsec=frontcover&img=1&zoom=1&edge=curl&source=gbs_api"
            },
            "language": "en",
            "previewLink": "http://books.google.co.in/books?id=An4_e3Cr3zAC&printsec=frontcover&dq=game&hl=&cd=1&source=gbs_api",
            "infoLink": "http://books.google.co.in/books?id=An4_e3Cr3zAC&dq=game&hl=&source=gbs_api",
            "canonicalVolumeLink": "http://books.google.co.in/books/about/The_Rules_of_the_Game.html?hl=&id=An4_e3Cr3zAC"
        },
        "saleInfo": {
            "country": "IN",
            "saleability": "FOR_SALE",
            "isEbook": true,
            "listPrice": {
                "amount": 399.0,
                "currencyCode": "INR"
            },
            "retailPrice": {
                "amount": 279.3,
                "currencyCode": "INR"
            },
            "buyLink": "http://books.google.co.in/books?id=An4_e3Cr3zAC&dq=game&hl=&buy=&source=gbs_api",
            "offers": [
                {
                    "finskyOfferType": 1,
                    "listPrice": {
                        "amountInMicros": 3.99E8,
                        "currencyCode": "INR"
                    },
                    "retailPrice": {
                        "amountInMicros": 2.793E8,
                        "currencyCode": "INR"
                    }
                }
            ]
        },
        "accessInfo": {
            "country": "IN",
            "viewability": "PARTIAL",
            "embeddable": true,
            "publicDomain": false,
            "textToSpeechPermission": "ALLOWED",
            "epub": {
                "isAvailable": true,
                "acsTokenLink": "http://books.goo"
            },
            "pdf": {
                "isAvailable": true,
                "acsTokenLink": "http://books.google.co.in/books/download/The_Rules_of_the_Game-sample-pdf.acsm?id=An4_e3Cr3zAC&format=pdf&output=acs4_fulfillment_token&dl_type=sample&source=gbs_api"
            },
            "webReaderLink": "http://books.google.co.in/books/reader?id=An4_e3Cr3zAC&hl=&printsec=frontcover&output=reader&source=gbs_api",
            "accessViewStatus": "SAMPLE",
            "quoteSharingAllowed": false
        },
        "searchInfo": {
            "textSnippet": "He's tested the specific material."
        }
    }
 ]

}

这是stacktrace表单logcathttps://codeshare.io/Ag78v

Answer 1

其中一个ListItem VolumeInfo的标题值为空。默认情况下，Gson不会解析空值。但在解析时，可以使其忽略空值。通过执行以下操作

Gson Gson=new GsonBuilder（）。序列化null（）。创建（）

试试这个

Answer 2

您没有使用serializedName注释。在模型中使用它，如下所示

     public class Items    
      {
        @SerializedName("Your-key-from JSON Response")
        private SaleInfo saleInfo;

        @SerializedName("Your-key-from JSON Response")
        private String id;

        @SerializedName("Your-key-from JSON Response")
        private SearchInfo searchInfo;

        @SerializedName("Your-key-from JSON Response")
        private String etag;

        @SerializedName("Your-key-from JSON Response")
        private VolumeInfo volumeInfo;

        @SerializedName("Your-key-from JSON Response")
        private String selfLink;

        @SerializedName("Your-key-from JSON Response")
        private AccessInfo accessInfo;

        @SerializedName("Your-key-from JSON Response")
        private String kind;

        public SaleInfo getSaleInfo ()
        {
            return saleInfo;
        }

        public void setSaleInfo (SaleInfo saleInfo)
        {
            this.saleInfo = saleInfo;
        }

        public String getId ()
        {
            return id;
        }

        public void setId (String id)
        {
            this.id = id;
        }
   }

Answer 3

将您的Items类替换为以下内容：

public class Items
{
private SaleInfo saleInfo;

private String id;

private SearchInfo searchInfo;

private String etag;

private VolumeInfo volumeInfo;

private String selfLink;

private AccessInfo accessInfo;

private String kind;

public SaleInfo getSaleInfo ()
{
    return saleInfo;
}

public void setSaleInfo (SaleInfo saleInfo)
{
    this.saleInfo = saleInfo;
}

public String getId ()
{
    return id;
}

public void setId (String id)
{
    this.id = id;
}

public SearchInfo getSearchInfo ()
{
    return searchInfo;
}

public void setSearchInfo (SearchInfo searchInfo)
{
    this.searchInfo = searchInfo;
}

public String getEtag ()
{
    return etag;
}

public void setEtag (String etag)
{
    this.etag = etag;
}

public VolumeInfo getVolumeInfo() {
    return volumeInfo;
}

public void setVolumeInfo(VolumeInfo volumeInfo) {
    this.volumeInfo = volumeInfo;
}

public String getSelfLink ()
{
    return selfLink;
}

public void setSelfLink (String selfLink)
{
    this.selfLink = selfLink;
}

public AccessInfo getAccessInfo ()
{
    return accessInfo;
}

public void setAccessInfo (AccessInfo accessInfo)
{
    this.accessInfo = accessInfo;
}

public String getKind ()
{
    return kind;
}

public void setKind (String kind)
{
    this.kind = kind;
}
}