权限

  <uses-permission android:name="android.permission.INTERNET" />
  <uses-permission 
   android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

使用HttpURLConnection

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;

import android.app.Activity;
import android.app.Dialog;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.view.Window;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

public class DownloadFileUseHttpURLConnection extends Activity {

ProgressBar pb;
Dialog dialog;
int downloadedSize = 0;
int totalSize = 0;
TextView cur_val;
String dwnload_file_path =  
"http://coderzheaven.com/sample_folder/sample_file.png";
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    Button b = (Button) findViewById(R.id.b1);
    b.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {
             showProgress(dwnload_file_path);

                new Thread(new Runnable() {
                    public void run() {
                         downloadFile();
                    }
                  }).start();
        }
    });
}

void downloadFile(){

    try {
        URL url = new URL(dwnload_file_path);
        HttpURLConnection urlConnection = (HttpURLConnection)   
 url.openConnection();

        urlConnection.setRequestMethod("GET");
        urlConnection.setDoOutput(true);

        //connect
        urlConnection.connect();

        //set the path where we want to save the file           
        File SDCardRoot = Environment.getExternalStorageDirectory(); 
        //create a new file, to save the downloaded file 
        File file = new File(SDCardRoot,"downloaded_file.png");

        FileOutputStream fileOutput = new FileOutputStream(file);

        //Stream used for reading the data from the internet
        InputStream inputStream = urlConnection.getInputStream();

        //this is the total size of the file which we are downloading
        totalSize = urlConnection.getContentLength();

        runOnUiThread(new Runnable() {
            public void run() {
                pb.setMax(totalSize);
            }               
        });

        //create a buffer...
        byte[] buffer = new byte[1024];
        int bufferLength = 0;

        while ( (bufferLength = inputStream.read(buffer)) > 0 ) {
            fileOutput.write(buffer, 0, bufferLength);
            downloadedSize += bufferLength;
            // update the progressbar //
            runOnUiThread(new Runnable() {
                public void run() {
                    pb.setProgress(downloadedSize);
                    float per = ((float)downloadedSize/totalSize) *     
                    100;
                    cur_val.setText("Downloaded " + downloadedSize +  

                    "KB / " + totalSize + "KB (" + (int)per + "%)" );
                }
            });
        }
        //close the output stream when complete //
        fileOutput.close();
        runOnUiThread(new Runnable() {
            public void run() {
                // pb.dismiss(); // if you want close it..
            }
        });         

    } catch (final MalformedURLException e) {
        showError("Error : MalformedURLException " + e);        
        e.printStackTrace();
    } catch (final IOException e) {
        showError("Error : IOException " + e);          
        e.printStackTrace();
    }
    catch (final Exception e) {
        showError("Error : Please check your internet connection " +  
e);
    }       
}

void showError(final String err){
    runOnUiThread(new Runnable() {
        public void run() {
            Toast.makeText(DownloadFileDemo1.this, err,  
      Toast.LENGTH_LONG).show();
        }
    });
}

void showProgress(String file_path){
    dialog = new Dialog(DownloadFileDemo1.this);
    dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
    dialog.setContentView(R.layout.myprogressdialog);
    dialog.setTitle("Download Progress");

    TextView text = (TextView) dialog.findViewById(R.id.tv1);
    text.setText("Downloading file from ... " + file_path);
    cur_val = (TextView) dialog.findViewById(R.id.cur_pg_tv);
    cur_val.setText("Starting download...");
    dialog.show();

     pb = (ProgressBar)dialog.findViewById(R.id.progress_bar);
     pb.setProgress(0);
            pb.setProgressDrawable(
      getResources().getDrawable(R.drawable.green_progress));  
  }
}

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  
        } 
    }
});

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

不要忘记用新文件("/mnt/sdcard/…")替换"/sdcard…"，否则你会得到一个FileNotFoundException

我遇到了一个简单文件下载库 获取，重要的是，它有存储访问框架，内容提供程序和URI支持。如果有人还在寻找，可能会有帮助。

//AndroidX .tonyodev.fetch2:xfetch2:3.1.6

实现"com.tonyodev.fetch2:fetch2:3.0.12" //支持lib

需要的权限，如果你不是使用应用程序特定的目录。

< uses-permission android: name = " android.permission.WRITE_EXTERNAL_STORAGE " / >

< uses-permission android: name = " android.permission.READ_EXTERNAL_STORAGE " / >

网络权限

< uses-permission android: name = " android.permission.INTERNET " / >

private Fetch fetch;
FetchConfiguration fetchConfiguration = new FetchConfiguration.Builder(this)
                .setDownloadConcurrentLimit(3)//Concurrent Download limit
                .build();

        fetch = Fetch.Impl.getInstance(fetchConfiguration);

        String url = "http:www.example.com/test.txt";//URL of file
        String file = "/downloads/test.txt";//Path of file
        
        final Request request = new Request(url, file);
        request.setPriority(Priority.HIGH);
        request.setNetworkType(NetworkType.ALL);//Preferred network type
        request.addHeader("clientKey", "SD78DF93_3947&MVNGHE1WONG");//Auth header if any
        
        fetch.enqueue(request, updatedRequest -> {
            //Request was successfully enqueued for download.
        }, error -> {
            //An error occurred enqueuing the request.
        });

    }

倾听更新和进展

FetchListener fetchListener = new FetchListener() {
    @Override
    public void onQueued(@NotNull Download download, boolean waitingOnNetwork) {
        if (request.getId() == download.getId()) {
            showDownloadInList(download);
        }
    }

    @Override
    public void onCompleted(@NotNull Download download) {

    }

    @Override
    public void onError(@NotNull Download download) {
        Error error = download.getError();
    }

    @Override
    public void onProgress(@NotNull Download download, long etaInMilliSeconds, long downloadedBytesPerSecond) {
        if (request.getId() == download.getId()) {
            updateDownload(download, etaInMilliSeconds);
        }
        int progress = download.getProgress();
    }

    @Override
    public void onPaused(@NotNull Download download) {

    }

    @Override
    public void onResumed(@NotNull Download download) {

    }

    @Override
    public void onCancelled(@NotNull Download download) {

    }

    @Override
    public void onRemoved(@NotNull Download download) {

    }

    @Override
    public void onDeleted(@NotNull Download download) {

    }
};

fetch.addListener(fetchListener);

//Remove listener when done.
fetch.removeListener(fetchListener);

此示例代码取自所有者页面，所有功劳都归于Tonyo Francis

我个人的建议是使用进度对话框并在执行前进行构建，或者在OnPreExecute()上初始化，如果你使用进度对话框的水平风格的进度条，则经常发布进度。剩下的部分是优化doInBackground的算法。