android使用AsyncTask实现多线程下载实例

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;  }}

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();        }      }    }  }}