private class DownloadTask extends AsyncTask<String, Integer, String> {

        private PowerManager.WakeLock mWakeLock;
        String onlinePathBundle, onlinePathMusic, offlinePathBundle, offlinePathMusic;

        CircleProgressBar progressBar;
        RelativeLayout rl_progress;
        ImageView btn_download;
        TextView tv_progress;

        public DownloadTask(String onlinePathBundle, String onlinePathMusic, String offlinePathBundle, String offlinePathMusic, CircleProgressBar progressBar, RelativeLayout rl_progress, ImageView btn_download,
                            TextView tv_progress) {
            this.offlinePathBundle = offlinePathBundle;
            this.offlinePathMusic = offlinePathMusic;
            this.progressBar = progressBar;
            this.rl_progress = rl_progress;
            this.btn_download = btn_download;
            this.tv_progress = tv_progress;
            this.onlinePathBundle = onlinePathBundle;
            this.onlinePathMusic = onlinePathMusic;
        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            progressBar.setMax(100);
            rl_progress.setVisibility(View.VISIBLE);
            btn_download.setVisibility(View.GONE);

            PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);
            mWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, getClass().getName());
            mWakeLock.acquire();
        }

        @Override
        protected String doInBackground(String... sUrl) {
            String firstResult = downTask(onlinePathBundle, 1, offlinePathBundle);
            String seondResult = downTask(onlinePathMusic, 2, offlinePathMusic);
            if (firstResult != null) {
                Toast.makeText(SplashActivity.this, "Download error: " + firstResult, Toast.LENGTH_LONG).show();
                return firstResult;
            } else {
                return seondResult;
            }

        }

        @Override
        protected void onProgressUpdate(Integer... progress) {
            super.onProgressUpdate(progress);
            progressBar.setProgress(progress[0]);
            tv_progress.setText(progress[0] + "%");

        }

        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);
            rl_progress.setVisibility(View.GONE);
            btn_download.setVisibility(View.VISIBLE);
            if (result != null) {
                Toast.makeText(SplashActivity.this, "Download error: " + result, Toast.LENGTH_LONG).show();
            } else {
                rl_progress.setVisibility(View.GONE);
                btn_download.setVisibility(View.GONE);
            }

        }

        public String downTask(String onlineNewPath, int numberOfTask, String offlineNewPath) {
            InputStream input = null;
            OutputStream output = null;
            HttpURLConnection connection = null;
            try {
                URL url = new URL(onlineNewPath);
                connection = (HttpURLConnection) url.openConnection();
                connection.connect();

                // expect HTTP 200 OK, so we don't mistakenly save error report
                // instead of the file
                if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
                    return "Server returned HTTP " + connection.getResponseCode()
                            + " " + connection.getResponseMessage();
                }

                // this will be useful to display download percentage
                // might be -1: server did not report the length
                int fileLength = connection.getContentLength();

                // download the file
                input = connection.getInputStream();
                output = new FileOutputStream(offlineNewPath);

                byte data[] = new byte[4096];
                long total = 0;
                int count;
                while ((count = input.read(data)) != -1) {
                    // allow canceling with back button
                    if (isCancelled()) {
                        input.close();
                        return null;
                    }
                    total += count;
                    // publishing the progress....
                    if (fileLength > 0) {// only if total length is known
                        if (numberOfTask == 1) {
                            publishProgress((int) (total * 50 / fileLength));
                        } else if (numberOfTask == 2) {
                            publishProgress(((int) (total * 50 / fileLength)) + 50);
                        }

                    }
                    output.write(data, 0, count);
                }
            } catch (Exception e) {
                return e.toString();
            } finally {
                try {
                    if (output != null)
                        output.close();
                    if (input != null)
                        input.close();
                } catch (IOException ignored) {
                }

                if (connection != null)
                    connection.disconnect();
            }
            return null;
        }
    }

我们可以使用协程和工作管理器在kotlin中下载文件。

在build.gradle中添加一个依赖

    implementation "androidx.work:work-runtime-ktx:2.3.0-beta01"
    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:1.3.1"

WorkManager类

    import android.content.Context
    import android.os.Environment
    import androidx.work.CoroutineWorker
    import androidx.work.WorkerParameters
    import androidx.work.workDataOf
    import com.sa.chat.utils.Const.BASE_URL_IMAGE
    import com.sa.chat.utils.Constants
    import kotlinx.coroutines.delay
    import java.io.BufferedInputStream
    import java.io.File
    import java.io.FileOutputStream
    import java.net.URL

    class DownloadMediaWorkManager(appContext: Context, workerParams: WorkerParameters)
        : CoroutineWorker(appContext, workerParams) {

        companion object {
            const val WORK_TYPE = "WORK_TYPE"
            const val WORK_IN_PROGRESS = "WORK_IN_PROGRESS"
            const val WORK_PROGRESS_VALUE = "WORK_PROGRESS_VALUE"
        }

        override suspend fun doWork(): Result {

            val imageUrl = inputData.getString(Constants.WORK_DATA_MEDIA_URL)
            val imagePath = downloadMediaFromURL(imageUrl)

            return if (!imagePath.isNullOrEmpty()) {
                Result.success(workDataOf(Constants.WORK_DATA_MEDIA_URL to imagePath))
            } else {
                Result.failure()
            }
        }

        private suspend fun downloadMediaFromURL(imageUrl: String?): String? {

            val file = File(
                    getRootFile().path,
                    "IMG_${System.currentTimeMillis()}.jpeg"
            )

            val url = URL(BASE_URL_IMAGE + imageUrl)
            val connection = url.openConnection()
            connection.connect()

            val lengthOfFile = connection.contentLength
            // download the file
            val input = BufferedInputStream(url.openStream(), 8192)
            // Output stream
            val output = FileOutputStream(file)

            val data = ByteArray(1024)
            var total: Long = 0
            var last = 0

            while (true) {

                val count = input.read(data)
                if (count == -1) break
                total += count.toLong()

                val progress = (total * 100 / lengthOfFile).toInt()

                if (progress % 10 == 0) {
                    if (last != progress) {
                        setProgress(workDataOf(WORK_TYPE to WORK_IN_PROGRESS,
                                WORK_PROGRESS_VALUE to progress))
                    }
                    last = progress
                    delay(50)
                }
                output.write(data, 0, count)
            }

            output.flush()
            output.close()
            input.close()

            return file.path

        }

        private fun getRootFile(): File {

            val rootDir = File(Environment.getExternalStorageDirectory().absolutePath + "/AppName")

            if (!rootDir.exists()) {
                rootDir.mkdir()
            }

            val dir = File("$rootDir/${Constants.IMAGE_FOLDER}/")

            if (!dir.exists()) {
                dir.mkdir()
            }
            return File(dir.absolutePath)
        }
    }

开始下载通过工作管理器在活动类

 private fun downloadImage(imagePath: String?, id: String) {

            val data = workDataOf(WORK_DATA_MEDIA_URL to imagePath)
            val downloadImageWorkManager = OneTimeWorkRequestBuilder<DownloadMediaWorkManager>()
                    .setInputData(data)
                    .addTag(id)
                    .build()

            WorkManager.getInstance(this).enqueue(downloadImageWorkManager)

            WorkManager.getInstance(this).getWorkInfoByIdLiveData(downloadImageWorkManager.id)
                    .observe(this, Observer { workInfo ->

                        if (workInfo != null) {
                            when {
                                workInfo.state == WorkInfo.State.SUCCEEDED -> {
                                    progressBar?.visibility = View.GONE
                                    ivDownload?.visibility = View.GONE
                                }
                                workInfo.state == WorkInfo.State.FAILED || workInfo.state == WorkInfo.State.CANCELLED || workInfo.state == WorkInfo.State.BLOCKED -> {
                                    progressBar?.visibility = View.GONE
                                    ivDownload?.visibility = View.VISIBLE
                                }
                                else -> {
                                    if(workInfo.progress.getString(WORK_TYPE) == WORK_IN_PROGRESS){
                                        val progress = workInfo.progress.getInt(WORK_PROGRESS_VALUE, 0)
                                        progressBar?.visibility = View.VISIBLE
                                        progressBar?.progress = progress
                                        ivDownload?.visibility = View.GONE

                                    }
                                }
                            }
                        }
                    })

        }

重要的

AsyncTask在Android 11中已弃用。

欲了解更多信息，请查看以下帖子

Android AsyncTask API在Android 11中已弃用。有什么替代方案? https://developer.android.com/reference/android/os/AsyncTask

可能应该移动到谷歌建议的并发框架

使用Android查询库，确实很酷。你可以改变它使用ProgressDialog，就像你在其他例子中看到的那样，这个将从你的布局中显示进度视图，并在完成后隐藏它。

File target = new File(new File(Environment.getExternalStorageDirectory(), "ApplicationName"), "tmp.pdf");
new AQuery(this).progress(R.id.progress_view).download(_competition.qualificationScoreCardsPdf(), target, new AjaxCallback<File>() {
    public void callback(String url, File file, AjaxStatus status) {
        if (file != null) {
            // do something with file  
        } 
    }
});

我正在为我现在使用的其他解决方案添加另一个答案，因为Android查询太大了，无法保持健康。所以我搬到了这个https://github.com/amitshekhariitbhu/Fast-Android-Networking。

    AndroidNetworking.download(url,dirPath,fileName).build()
      .setDownloadProgressListener(new DownloadProgressListener() {
        public void onProgress(long bytesDownloaded, long totalBytes) {
            bar.setMax((int) totalBytes);
            bar.setProgress((int) bytesDownloaded);
        }
    }).startDownload(new DownloadListener() {
        public void onDownloadComplete() {
            ...
        }

        public void onError(ANError error) {
            ...
        }
    });

我推荐你使用我的Project Netroid，它是基于Volley的。我添加了一些功能，如多事件回调，文件下载管理。这可能会有帮助。