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
AsyncDownload.png
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();
}
}
}
}
}
