如何在android中同时下载多个文件？

import android.app.ProgressDialog;
import android.content.Context;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "MainActivity";
    private static final String FILE_URL1 = "https://example.com/file1.txt";
    private static final String FILE_URL2 = "https://example.com/file2.txt";
    private static final String FILE_URL3 = "https://example.com/file3.txt";

    private Button downloadButton;
    private ProgressDialog progressDialog;

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

        downloadButton = findViewById(R.id.download_button);
        downloadButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                downloadFiles();
            }
        });
    }

    private void downloadFiles() {
        List<String> fileUrls = new ArrayList<>();
        fileUrls.add(FILE_URL1);
        fileUrls.add(FILE_URL2);
        fileUrls.add(FILE_URL3);

        DownloadTask downloadTask = new DownloadTask(this);
        downloadTask.execute(fileUrls);
    }

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

        private Context context;

        public DownloadTask(Context context) {
            this.context = context;
        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            progressDialog = new ProgressDialog(context);
            progressDialog.setMessage("Downloading files...");
            progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
            progressDialog.setCancelable(false);
            progressDialog.show();
        }

        @Override
        protected Boolean doInBackground(List<String>... params) {
            List<String> fileUrls = params[0];
            int count = fileUrls.size();
            int progress = 0;

            try {
                for (String fileUrl : fileUrls) {
                    URL url = new URL(fileUrl);
                    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                    connection.connect();

                    int fileLength = connection.getContentLength();

                    File directory = new File(Environment.getExternalStorageDirectory().getPath() + "/Download");
                    if (!directory.exists()) {
                        directory.mkdirs();
                    }

                    File outputFile = new File(directory, fileUrl.substring(fileUrl.lastIndexOf("/") + 1));
                    FileOutputStream outputStream = new FileOutputStream(outputFile);

                    InputStream inputStream = new BufferedInputStream(url.openStream());

                    byte[] data = new byte[1024];
                    int total = 0;
                    int count;
                    while ((count = inputStream.read(data)) != -1) {
                        total += count;
                        outputStream.write(data, 0, count);
                        int progressPercentage = (int) ((total * 100) / fileLength);
                        publishProgress(progressPercentage);
                    }

                    outputStream.flush();
                    outputStream.close();
                    inputStream.close();

                    progress++;
                }
            } catch (Exception e) {
                Log.e(TAG, "Error downloading files: " + e.getMessage());
                return false;
            }

            return true;
        }

        @Override
        protected void onProgressUpdate(Integer... values) {
            super.onProgressUpdate(values);
            progressDialog.setProgress(values[0]);
        }

        @Override
        protected void onPostExecute(Boolean result) {
            super.onPostExecute(result);
            progressDialog.dismiss();

            if (result) {
                // All files downloaded successfully
                // TODO: Add your code here
            } else {
                // Error occurred while downloading files
                // TODO: Add your code here
            }
        }
    }
}