Как остановить выполнение кода?

Ситуация следующая - есть программа для просмотра PDF по ссылке и она работает

но есть один нюанс когда я выхожу из activity (Выхожу из activity через onBackPressed() ) в момент загрузки , то получается что программа все равно грузит документ. Хотя уже не надо .

public class MainActivity2 extends AppCompatActivity implements DownloadFile.Listener {
    
        LinearLayout root;
        RemotePDFViewPager remotePDFViewPager;
        Button btnDownload;
        PDFPagerAdapter adapter;
        ProgressBar progressBar;
    
        private Vibrator Vibro;
    
        public String loadUrl ="Тут будет ссылка";

        @Override
        public void onBackPressed() {
            finish();
        }
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main_activity2);
    
            Toast.makeText(getApplicationContext(), R.string.page_loading, Toast.LENGTH_SHORT ).show();
            progressBar = (ProgressBar) findViewById(R.id.progressBar);
            progressBar.setVisibility(View.VISIBLE);
            root = (LinearLayout) findViewById(R.id.remote_pdf_root);
                btnDownload = (Button) findViewById(R.id.btn_download);
            onClick(null);
        }
    
        @Override
        protected void onDestroy() {
            super.onDestroy();
    
            if (adapter != null) {
                adapter.close();
            }
        }

        public void showDownloadButton() {
            btnDownload.setVisibility(View.VISIBLE);
        }
    
        public void updateLayout() {
            root.removeAllViewsInLayout();
            root.addView(progressBar,
                    LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT);
            progressBar.setVisibility(View.GONE);
            root.addView(btnDownload,
                    LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT);
            root.addView(remotePDFViewPager,
                    LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT);
    
            Vibro = (Vibrator)this.getSystemService(VIBRATOR_SERVICE);
            Vibro.vibrate(50);
    
            Toast.makeText(getApplicationContext(), "мы тут ", Toast.LENGTH_SHORT ).show();
        }
    
        @Override
        public void onSuccess(String url, String destinationPath) {
            adapter = new PDFPagerAdapter(this, FileUtil.extractFileNameFromURL(url));
            remotePDFViewPager.setAdapter(adapter);
            updateLayout();
            showDownloadButton();
        }
    
        @Override
        public void onFailure(Exception e) {
            e.printStackTrace();
            showDownloadButton();
        }
    
        @Override
        public void onProgressUpdate(int progress, int total) {}
    
        public void onClick(View view) {
            final Context ctx = this;
            final DownloadFile.Listener listener = this;
            remotePDFViewPager = new RemotePDFViewPager(ctx, loadUrl, listener);
            remotePDFViewPager.setId(R.id.pdfViewPager);
        }
    }

/////

исходники RemotePDFViewPager

/*
 * Copyright (C) 2016 Olmo Gallegos Hernández.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package es.voghdev.pdfviewpager.library;

import android.content.Context;
import android.content.res.TypedArray;
import android.os.Handler;
import android.util.AttributeSet;
import android.view.MotionEvent;

import androidx.viewpager.widget.ViewPager;

import java.io.File;

import es.voghdev.pdfviewpager.library.remote.DownloadFile;
import es.voghdev.pdfviewpager.library.remote.DownloadFileUrlConnectionImpl;
import es.voghdev.pdfviewpager.library.util.FileUtil;

public class RemotePDFViewPager extends ViewPager implements DownloadFile.Listener {
    protected Context context;
    protected DownloadFile downloadFile;
    protected DownloadFile.Listener listener;

    public RemotePDFViewPager(Context context, String pdfUrl, DownloadFile.Listener listener) {
        super(context);
        this.context = context;
        this.listener = listener;

        init(new DownloadFileUrlConnectionImpl(context, new Handler(), this), pdfUrl);
    }

    public RemotePDFViewPager(Context context,
                              DownloadFile downloadFile,
                              String pdfUrl,
                              DownloadFile.Listener listener) {
        super(context);
        this.context = context;
        this.listener = listener;

        init(downloadFile, pdfUrl);
    }

    public RemotePDFViewPager(Context context, AttributeSet attrs) {
        super(context, attrs);
        this.context = context;

        init(attrs);
    }

    private void init(DownloadFile downloadFile, String pdfUrl) {
        setDownloader(downloadFile);
        downloadFile.download(pdfUrl,
                new File(context.getCacheDir(), FileUtil.extractFileNameFromURL(pdfUrl)).getAbsolutePath());
    }

    private void init(AttributeSet attrs) {
        if (attrs != null) {
            TypedArray a;

            a = context.obtainStyledAttributes(attrs, R.styleable.PDFViewPager);
            String pdfUrl = a.getString(R.styleable.PDFViewPager_pdfUrl);

            if (pdfUrl != null && pdfUrl.length() > 0) {
                init(new DownloadFileUrlConnectionImpl(context, new Handler(), this), pdfUrl);
            }

            a.recycle();
        }
    }

    public void setDownloader(DownloadFile downloadFile) {
        this.downloadFile = downloadFile;
    }

    @Override
    public void onSuccess(String url, String destinationPath) {
        listener.onSuccess(url, destinationPath);
    }

    @Override
    public void onFailure(Exception e) {
        listener.onFailure(e);
    }

    @Override
    public void onProgressUpdate(int progress, int total) {
        listener.onProgressUpdate(progress, total);
    }

    /**
     * PDFViewPager uses PhotoView, so this bugfix should be added
     * Issue explained in https://github.com/chrisbanes/PhotoView
     */
    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        try {
            return super.onInterceptTouchEvent(ev);
        } catch (IllegalArgumentException e) {
            e.printStackTrace();
            return false;
        }
    }

    public class NullListener implements DownloadFile.Listener {
        public void onSuccess(String url, String destinationPath) {
            /* Empty */
        }

        public void onFailure(Exception e) {
            /* Empty */
        }

        public void onProgressUpdate(int progress, int total) {
            /* Empty */
        }
    }
}

////

DownloadFileUrlConnectionImpl

/*
 * Copyright (C) 2016 Olmo Gallegos Hernández.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package es.voghdev.pdfviewpager.library.remote;

import android.content.Context;
import android.os.Handler;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

public class DownloadFileUrlConnectionImpl implements DownloadFile {
    private static final int KILOBYTE = 1024;

    private static final int BUFFER_LEN = 1 * KILOBYTE;
    private static final int NOTIFY_PERIOD = 150 * KILOBYTE;

    Context context;
    Handler uiThread;
    Listener listener = new NullListener();

    public DownloadFileUrlConnectionImpl(Context context, Handler uiThread, Listener listener) {
        this.context = context;
        this.uiThread = uiThread;
        this.listener = listener;
    }

    @Override
    public void download(final String url, final String destinationPath) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    File file = new File(destinationPath);
                    FileOutputStream fileOutput = new FileOutputStream(file);
                    HttpURLConnection urlConnection = null;
                    URL urlObj = new URL(url);
                    urlConnection = (HttpURLConnection) urlObj.openConnection();
                    int totalSize = urlConnection.getContentLength();
                    int downloadedSize = 0;
                    int counter = 0;
                    byte[] buffer = new byte[BUFFER_LEN];
                    int bufferLength = 0;
                    InputStream in = new BufferedInputStream(urlConnection.getInputStream());

                    while ((bufferLength = in.read(buffer)) > 0) {
                        fileOutput.write(buffer, 0, bufferLength);
                        downloadedSize += bufferLength;
                        counter += bufferLength;
                        if (listener != null && counter > NOTIFY_PERIOD) {
                            notifyProgressOnUiThread(downloadedSize, totalSize);
                            counter = 0;
                        }
                    }

                    urlConnection.disconnect();
                    fileOutput.close();

                    notifySuccessOnUiThread(url, destinationPath);
                } catch (MalformedURLException e) {
                    notifyFailureOnUiThread(e);
                } catch (IOException e) {
                    notifyFailureOnUiThread(e);
                }
            }
        }).start();
    }

    protected void notifySuccessOnUiThread(final String url, final String destinationPath) {
        if (uiThread == null) {
            return;
        }

        uiThread.post(new Runnable() {
            @Override
            public void run() {
                listener.onSuccess(url, destinationPath);
            }
        });
    }

    protected void notifyFailureOnUiThread(final Exception e) {
        if (uiThread == null) {
            return;
        }

        uiThread.post(new Runnable() {
            @Override
            public void run() {
                listener.onFailure(e);
            }
        });
    }

    private void notifyProgressOnUiThread(final int downloadedSize, final int totalSize) {
        if (uiThread == null) {
            return;
        }

        uiThread.post(new Runnable() {
            @Override
            public void run() {
                listener.onProgressUpdate(downloadedSize, totalSize);
            }
        });
    }

    protected class NullListener implements Listener {
        public void onSuccess(String url, String destinationPath) {
            /* Empty */
        }

        public void onFailure(Exception e) {
            /* Empty */
        }

        public void onProgressUpdate(int progress, int total) {
            /* Empty */
        }
    }
}

////

DownloadFile

/*
 * Copyright (C) 2016 Olmo Gallegos Hernández.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package es.voghdev.pdfviewpager.library.remote;

public interface DownloadFile {
    void download(String url, String destinationPath);

    interface Listener {
        void onSuccess(String url, String destinationPath);

        void onFailure(Exception e);

        void onProgressUpdate(int progress, int total);
    }
}

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