android使用AsyncTask实现多线程下载实例

AsyncTask不仅方便我们在子线程中对UI进行更新操作，还可以借助其本身的线程池来实现多线程任务。下面是一个使用AsyncTask来实现的多线程下载例子。

01 效果图

02 核心类 - DownloadTask.class

public class DownloadTask extends AsyncTask<String, Integer, Integer> {
 public static final int TYPE_SUCCESS = 0;
 public static final int TYPE_FAILURE = 1;
 public static final int TYPE_PAUSE = 2;
 public static final int TYPE_CANCEL = 3;

public int positionDownload;

private boolean isPaused = false;
 private boolean isCancelled = false;

private DownloadListener downloadListener;
 private int lastProgress;

public DownloadTask(DownloadListener downloadListener){
   this.downloadListener = downloadListener;
 }

public void setDownloadListener(DownloadListener downloadListener){
   this.downloadListener = downloadListener;
 }

@Override
 protected Integer doInBackground(String... params) {
   InputStream is = null;
   RandomAccessFile savedFile = null;
   File file = null;

long downloadLength = 0;
   String downloadUrl = params[0];
   positionDownload = Integer.parseInt(params[1]);
   String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/"));
   String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();
   file = new File(directory + fileName);

if(file.exists()){
     downloadLength = file.length();
   }

long contentLength = getContentLength(downloadUrl);
   if(contentLength == 0){
     return TYPE_FAILURE;
   } else if(contentLength == downloadLength){
     return TYPE_SUCCESS;
   }

OkHttpClient client = new OkHttpClient();
   Request request = new Request.Builder()
                 .addHeader("RANGE", "bytes="+downloadLength+"-")
                 .url(downloadUrl)
                 .build();
   try {
     Response response = client.newCall(request).execute();
     if(response != null){
       is = response.body().byteStream();
       savedFile = new RandomAccessFile(file, "rw");
       savedFile.seek(downloadLength);
       byte[] buffer = new byte[1024];
       int total = 0;
       int length;

while((length = is.read(buffer)) != -1){
         if(isCancelled){
           response.body().close();
           return TYPE_CANCEL;
         } else if(isPaused) {
           response.body().close();
           return TYPE_PAUSE;
         }

total += length;
         savedFile.write(buffer, 0, length);

int progress = (int) ((total + downloadLength) * 100 / contentLength);
         int currentDownload = (int) (total + downloadLength);
         publishProgress(positionDownload, progress, currentDownload, (int) contentLength);
       }

response.body().close();
       return TYPE_SUCCESS;
     }
   } catch (IOException e) {
     e.printStackTrace();
   } finally {
     try {
       if(is != null) is.close();
       if(savedFile != null) savedFile.close();
       if(isCancelled && file != null) file.delete();
     } catch (IOException e) {
       e.printStackTrace();
     }
   }

return TYPE_FAILURE;
 }

@Override
 protected void onProgressUpdate(Integer... values) {
   int progress = values[1];
   if(progress > lastProgress){
     downloadListener.onProgress(values[0], progress, values[2], values[3]);
     lastProgress = progress;
   }
 }

@Override
 protected void onPostExecute(Integer status) {
   switch (status){
     case TYPE_SUCCESS:
       downloadListener.onSuccess(positionDownload);
       break;
     case TYPE_FAILURE:
       downloadListener.onFailure();
       break;
     case TYPE_PAUSE:
       downloadListener.onPause();
       break;
     case TYPE_CANCEL:
       downloadListener.onCancel();
       break;
   }
 }

public void pauseDownload(){
   isPaused = true;
 }

public void cancelDownload(){
   isCancelled = true;
 }

private long getContentLength(String downloadUrl) {
   OkHttpClient client = new OkHttpClient();
   Request request = new Request.Builder()
                 .url(downloadUrl)
                 .build();
   Response response = null;
   try {
     response = client.newCall(request).execute();
     if(response != null && response.isSuccessful()){
       long contentLength = response.body().contentLength();
       response.body().close();
       return contentLength;
     }
   } catch (IOException e) {
     e.printStackTrace();
   }

return 0;
 }
}

03 核心类 - DownloadService.class

public class DownloadService extends Service {
 private Map<String, DownloadTask> downloadTaskMap = new HashMap<>();

private DownloadBinder mBinder = new DownloadBinder();

@Override
 public IBinder onBind(Intent intent) {
   return mBinder;
 }

private Notification getNotification(String title, int progress) {
   Intent intent = new Intent(this, MainActivity.class);
   PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intent, 0);

NotificationCompat.Builder builder = new NotificationCompat.Builder(this);
   builder.setSmallIcon(R.mipmap.ic_launcher);
   builder.setLargeIcon(BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher));
   builder.setContentIntent(pendingIntent);
   builder.setContentTitle(title);
   if(progress > 0){
     builder.setContentText(progress + "％");
     builder.setProgress(100, progress, false);
   }

return builder.build();
 }

private NotificationManager getNotificationManager() {
   return (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
 }

class DownloadBinder extends Binder {
   public void startDownload(String url, int position, DownloadListener listener){
     if(!downloadTaskMap.containsKey(url)){
       DownloadTask downloadTask = new DownloadTask(listener);
       downloadTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, url, position+"");
       downloadTaskMap.put(url, downloadTask);
       if(downloadTaskMap.size() == 1){
         startForeground(1, getNotification("正在下载" + downloadTaskMap.size(), -1));
       } else{
         getNotificationManager().notify(1, getNotification("正在下载" + downloadTaskMap.size(), -1));
       }
     }
   }

public void updateDownload(String url, DownloadListener listener){
     if(downloadTaskMap.containsKey(url)){
       DownloadTask downloadTask = downloadTaskMap.get(url);
       if(downloadTask != null){
         downloadTask.setDownloadListener(listener);
       }
     }

}

public void pauseDownload(String url){
     if(downloadTaskMap.containsKey(url)){
       DownloadTask downloadTask = downloadTaskMap.get(url);
       if(downloadTask != null){
         downloadTask.pauseDownload();
       }

downloadTaskMap.remove(url);

if(downloadTaskMap.size() > 0){
         getNotificationManager().notify(1, getNotification("正在下载" + downloadTaskMap.size(), -1));
       } else {
         stopForeground(true);
         getNotificationManager().notify(1, getNotification("全部暂停下载", -1));
       }
     }
   }

public void downloadSuccess(String url){
     if(downloadTaskMap.containsKey(url)){
       DownloadTask downloadTask = downloadTaskMap.get(url);
       downloadTaskMap.remove(url);
       if(downloadTask != null){
         downloadTask = null;
       }

if(downloadTaskMap.size() > 0){
         getNotificationManager().notify(1, getNotification("正在下载" + downloadTaskMap.size(), -1));
       } else {
         stopForeground(true);
         getNotificationManager().notify(1, getNotification("下载成功", -1));
       }

}
   }

public boolean isDownloading(String url){
     if(downloadTaskMap.containsKey(url)){
       return true;
     }

return false;
   }

public void cancelDownload(String url){
     if(downloadTaskMap.containsKey(url)){
       DownloadTask downloadTask = downloadTaskMap.get(url);
       if(downloadTask != null){
         downloadTask.cancelDownload();
       }
       downloadTaskMap.remove(url);

if(downloadTaskMap.size() > 0){
         getNotificationManager().notify(1, getNotification("正在下载" + downloadTaskMap.size(), -1));
       } else {
         stopForeground(true);
         getNotificationManager().notify(1, getNotification("全部取消下载", -1));
       }
     }

if(url != null){
       String fileName = url.substring(url.lastIndexOf("/"));
       String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();
       File file = new File(directory + fileName);

if(file.exists()){
         file.delete();
         Toast.makeText(DownloadService.this, "Deleted", Toast.LENGTH_SHORT).show();
       }
     }
   }
 }
}

04 源码

下载地址

来源：http://www.jianshu.com/p/a3f23afc0494