将多个文件上传到 AsyncTask 时出现问题

帮助处理错误：在 RecyclerView 中，当您单击一个元素时，会转换到带有“下载”和“读取”按钮的活动。当您单击“加载”时，将启动 AsyncTask（加载 url 列表）。下载后，按钮变为非活动状态（条件是有一个包含下载文件的文件夹）。当您单击“阅读”时，将切换到另一个活动以查看图片。有条件 - 这是第一本书，它的文件供查看。因此，当您尝试下载第二本书时，表面上一切都很好，但无法查看文件 - 它们没有加载。在调试器中，我运行了两本书的下载周期——它工作不稳定，然后一个文件将加载七个文件，然后一切都完全正常。如果我清理应用程序数据，我首先加载的书可以正常工作。

import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
import com.tonyodev.fetch.Fetch;
import com.tonyodev.fetch.request.Request;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import org.json.JSONTokener;

import java.io.BufferedReader;
import java.io.File;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.lang.reflect.Type;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutionException;

import ru.yandex.matu1.toddlersbook.models.Book;
import ru.yandex.matu1.toddlersbook.models.BookFiles;

public class BookCardActivity extends AppCompatActivity {
    static final String TAG = "myLogs";
    private int bookId;
    private String fileNamePath = "filesPath.json";

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

        BookUriFromId();

        String covers = MyJSON.getData(this, fileNamePath);
        ArrayList<String> coversPaths = getFilesPathFromFile(covers);

        ImageView imageView = (ImageView) findViewById(R.id.imageView);
        int posit = bookId-1;
        File imgFile = new File(coversPaths.get(posit));
        Bitmap myBitmap = BitmapFactory.decodeFile(imgFile.getAbsolutePath());
        imageView.setImageBitmap(myBitmap);

        Button buttonDownload = (Button) findViewById(R.id.button);
        Button buttonRead = (Button) findViewById(R.id.button2);

        String fileBookSt = "book_" + bookId + ".json";
        File fileOfBook = new File(getApplicationContext().getFilesDir().getPath() + File.separator + fileBookSt);

        if(fileOfBook.exists()){
            buttonDownload.setEnabled(false);
        }

        buttonDownload.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Type itemsListType = new TypeToken<List<String>>() {
                }.getType();
                String folderB = "bookfiles_" + bookId;
                String fileBookStorage = "book_" + bookId + ".json";

                    BookLoader bookLoader = new BookLoader();
                    bookLoader.execute();

                    ArrayList<String> pagesPath;
                    ArrayList<String> soundsPath;
                    soundsPath = new ArrayList<>();


                    File bookfolder = new File(String.valueOf(getExternalFilesDir(folderB)));

                    if (!bookfolder.exists()) {
                        bookfolder.mkdirs();
                        Log.d("my", "dir. created");
                    }

                    try {
                        String result = bookLoader.get();
                        Gson gson = new Gson();
                        Book book = gson.fromJson(result, Book.class);
                        List<String> pages = book.getPageUrl();
                        String[] urlsPages = pages.toArray(new String[0]);

                        FileLoader fileLoader = new FileLoader();
                        fileLoader.execute(urlsPages);
                        String flResult = fileLoader.get();

                        pagesPath = new Gson().fromJson(flResult, itemsListType);

                        BookFiles bookFiles = new BookFiles();
                        bookFiles.setBookID(bookId);
                        bookFiles.setPagesPath(pagesPath);
                        bookFiles.setSoundsPath(soundsPath);

                        Gson gson11 = new Gson();
                        String filesJson = gson11.toJson(bookFiles);

                        MyJSON.saveData(getApplicationContext(), filesJson, fileBookStorage);

                    } catch (InterruptedException | ExecutionException e) {
                        e.printStackTrace();
                    }
//                }
            }
        });
    buttonRead.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            NextActivity();
        }
    });

    }

    private class BookLoader extends AsyncTask<Void, Void, String> {

        HttpURLConnection urlConnection = null;
        BufferedReader reader = null;
        String resultJsonBook = "";
        private String bookIdJson = "http://*****.ru/todbook/book" + bookId + ".json";

        @Override
        protected String doInBackground(Void... voids) {
            try {
                URL url = new URL(bookIdJson);

                urlConnection = (HttpURLConnection) url.openConnection();
                urlConnection.setRequestMethod("GET");
                urlConnection.connect();

                InputStream inputStream = urlConnection.getInputStream();
                StringBuffer buffer = new StringBuffer();

                reader = new BufferedReader(new InputStreamReader(inputStream));

                String line;
                while ((line = reader.readLine()) != null) {
                    buffer.append(line);
                }

                resultJsonBook = buffer.toString();

            } catch (Exception e) {
                e.printStackTrace();
            }
            return resultJsonBook;
        }

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

    }

    private class FileLoader extends AsyncTask<String, Void, String> {
        Fetch mFetch;
        String folderB = "bookfiles_" + bookId;
        File bookfolder = new File(String.valueOf(getExternalFilesDir(folderB)));
        List<Request> requestListPages = new ArrayList<>();
        ArrayList<String> pagesPath = new ArrayList<>();
        String resultD;

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

            mFetch = Fetch.newInstance(getApplicationContext());
            mFetch.removeRequests(); //чистим базу запросов

            for (int i = 0; i < urlsFiles.length; i++) {
                String url = urlsFiles[i];
                String path = String.valueOf(bookfolder);
                String fileName = Uri.parse(url).getLastPathSegment();
                Log.d("my2", fileName);
                Request request = new Request(url, path, fileName);
                requestListPages.add(request);
                String pageFilePath = path + "/" + fileName;
                Log.d("my2", pageFilePath);
                pagesPath.add(pageFilePath);
            }

            mFetch.enqueue(requestListPages);
//            resultD = String.valueOf(pagesPath);
            String resultD = new Gson().toJson(pagesPath);
            return resultD;

        }

    }

    private void BookUriFromId() {
        //получаем номер ID книги, с обложки которой перешли в слайдер
        Intent intent = getIntent();
        bookId = intent.getIntExtra("bookId", 1);
        Log.d(TAG, "You read book №" + bookId);
    }

    private void NextActivity() {
        new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                Intent intent = new Intent(BookCardActivity.this, SliderActivity.class);
                intent.putExtra("bookId", bookId); // передаю в слайдер номер книги

                startActivity(intent);
                finish();
            }
        }, 20);
    }

    private ArrayList<String> getFilesPathFromFile(String jsResult) {
        ArrayList<String> urisImg = new ArrayList<>();
        try {
            JSONArray rootJson = new JSONArray(new JSONTokener(jsResult));
            for (int i = 0; i < rootJson.length(); i++) {
                JSONObject o = rootJson.getJSONObject(i);
                String strTo = (String) o.get("uriString");
                urisImg.add(strTo);
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return urisImg;
    }

}