运行Android中的多个并行下载 [英] Running multiple parallel downloads in Android
问题描述
首先，我延长 IntentService 来建立我的 DonwloadService 类。这是确定的，但一个下载队列已经建立和2下载不得不等待1到成品等。
First, I extended IntentService to build my DonwloadService class. It was OK, but a download queue had been created and 2nd download had to wait for the 1st to finished etc.
所以我决定延长服务类（遵循的文档）。我刚刚添加下载功能和功能发布的结果（在活动接收器收听）：
So I decided to extend Service class (following the docs). I've just added download function and function for publishing results (listened by receiver in activity):
public class DownloadService extends Service
{
private static final String TAG = DownloadService.class.getSimpleName();
public static final String EXTRA_DOWNLOAD = "EXTRA_DOWNLOAD";
public static final String EXTRA_POSITION = "EXTRA_POSITION";
public static final String INTENT_NOTIFICATION = "INTENT_NOTIFICATION";
public static final String EXTRA_RESULT = "EXTRA_RESULT";
public static final String EXTRA_PROGRESS = "EXTRA_PROGRESS";
public static final String EXTRA_PATH = "EXTRA_PATH";
public static final String EXTRA_INDETERMINABLE = "EXTRA_INDETERMINABLE";
public static final int RESULT_PROGRESS = 123;
private int mResult = Activity.RESULT_CANCELED;
private Looper mServiceLooper;
private ServiceHandler mServiceHandler;
private final class ServiceHandler extends Handler
{
public ServiceHandler(Looper looper)
{
super(looper);
}
@Override
public void handleMessage(Message message)
{
// Download file
download(message.getData());
// Stop the service using the startId, so that we don't stop
// the service in the middle of handling another job
stopSelf(message.arg1);
}
}
@Override
public void onCreate()
{
// Start up the thread running the service. Note that we create a
// separate thread because the service normally runs in the process's
// main thread, which we don't want to block. We also make it
// background priority so CPU-intensive work will not disrupt our UI.
HandlerThread handlerThread = new HandlerThread("DownloadServiceStartArguments",
Process.THREAD_PRIORITY_BACKGROUND);
handlerThread.start();
// Get the HandlerThread's Looper and use it for our Handler
mServiceLooper = handlerThread.getLooper();
mServiceHandler = new ServiceHandler(mServiceLooper);
}
@Override
public int onStartCommand(Intent intent, int flags, int startId)
{
// For each start request, send a message to start a job and deliver the
// start ID so we know which request we're stopping when we finish the job
Message message = mServiceHandler.obtainMessage();
message.setData(intent.getExtras());
message.arg1 = startId;
mServiceHandler.sendMessage(message);
return START_REDELIVER_INTENT;
}
@Nullable
@Override
public IBinder onBind(Intent intent)
{
// No binding provided
return null;
}
@Override
public void onDestroy()
{
Log.d(TAG, "Service done");
}
/**
* Handles file download
*
* @param bundle
*/
private void download(Bundle bundle)
{
if (bundle != null) {
return;
}
Download download = bundle.getParcelable(EXTRA_DOWNLOAD);
int position = bundle.getInt(EXTRA_POSITION, -1);
File downloadedFile = new File(Environment.getExternalStorageDirectory(), position + ".jpg");
if (downloadedFile.exists()) {
downloadedFile.delete();
}
FileOutputStream fileOutputStream = null;
int filesize = -1;
try {
fileOutputStream = new FileOutputStream(downloadedFile.getPath());
URL url = new URL(download.getUrl());
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.connect();
filesize = connection.getContentLength();
InputStream reader = new BufferedInputStream(connection.getInputStream());
byte data[] = new byte[1024];
int next = -1;
int total = 0;
while ((next = reader.read(data)) != -1) {
mResult = RESULT_PROGRESS;
total += next;
publishResult(downloadedFile.getAbsolutePath(),
(filesize > 0) ? Math.round(total * 100 / filesize) : Math.round(total / 1024),
position, filesize <= 0);
fileOutputStream.write(data, 0, next);
}
mResult = Activity.RESULT_OK;
} catch (Exception e) {
e.printStackTrace();
} finally {
if (fileOutputStream != null) {
try {
fileOutputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
publishResult(downloadedFile.getAbsolutePath(), 100, position, filesize <= 0);
}
private void publishResult(String downloadPath, int progress, int positionInList,
boolean indeterminable)
{
Intent intent = new Intent(INTENT_NOTIFICATION);
intent.putExtra(EXTRA_PATH, downloadPath);
intent.putExtra(EXTRA_PROGRESS, progress);
intent.putExtra(EXTRA_POSITION, positionInList);
intent.putExtra(EXTRA_INDETERMINABLE, indeterminable);
intent.putExtra(EXTRA_RESULT, mResult);
sendBroadcast(intent);
}
}
但仍然有一个下载队列，没有并行下载。
But still there is a download queue, no parallel downloads.
推荐答案
如果你想在不同的数据集多次运行任务，但你只需要一个执行同时运行，一个 IntentService 适合您的需要。要自动运行的任务，只要有资源，或允许多个任务在同一时间（或两者）上运行，你需要提供的线程管理的集合。要做到这一点，使用的ThreadPoolExecutor 的一个实例，当其在池中的线程空闲运行从队列的任务。要运行一个任务，你所要做的就是把它添加到队列中。
If you want to run a task repeatedly on different sets of data, but you only need one execution running at a time, an IntentService suits your needs. To automatically run tasks as resources become available, or to allow multiple tasks to run at the same time (or both), you need to provide a managed collection of threads. To do this, use an instance of ThreadPoolExecutor, which runs a task from a queue when a thread in its pool becomes free. To run a task, all you have to do is add it to the queue.
参考：
用于创建多个线程管理器
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