ExoPlayer的缓存四缓存Cache 的应用

ExoPlayer的缓存-- 四 Cache 的使用

文章目录

缓存ID
- 默认的CacheID
- 改造后的CacheID
加密文件的处理
- 缓存下载 DefaultHttpDataSourceFactory
- CryptoWrapDataSource
文件分片大小
下载网速的计算
下载参数的设置 Builder 设计模式的使用
- 定义基类 ParametersBase
- Builder 类
- CacheDownloadParameters

缓存ID

默认的CacheID

同一文件内容服务器生成的链接有时效性，如果用URL做缓存ID，会出现同一首无法命中缓存的情况。Exoplayer 的缓存默认使用 URL

public static final CacheKeyFactory DEFAULT_CACHE_KEY_FACTORY =(dataSpec) -> dataSpec.key != null ? dataSpec.key : generateKey(dataSpec.uri);

每首歌曲有一个SongID, 如果使用SongID，每首歌曲的有伴奏原唱视频三种文件，也有冲突的可能。

因此使用URL 的path 作为SongID 是比较合适的。

改造后的CacheID

Exoplayer 在创建CacheDataSourceFactory 的时候传入CacheKeyFactory

        return new CacheDataSourceFactory(cache,new DefaultHttpDataSourceFactory("user-agent"),new FileDataSource.Factory(),new CacheDataSinkFactory(cache, CacheDataSink.DEFAULT_FRAGMENT_SIZE),CacheDataSource.FLAG_IGNORE_CACHE_ON_ERROR, null,new CacheKeyFactory() {@Overridepublic String buildCacheKey(DataSpec dataSpec) {return dataSpec.key != null ? dataSpec.key : dataSpec.uri.getLastPathSegment();}});
}

缓存的时候生成DownloadRequest 直接使用URL 的path 最为ID参数传入

DownloadRequest request = CacheDownloadManager.buildDownloadRequest(uri.getLastPathSegment(), uri);

加密文件的处理

缓存下载 DefaultHttpDataSourceFactory

K歌播放的文件时加密类型的，在缓存的时候直接使用DefaultHttpDataSourceFactory 下载流。

因此缓存的文件是加密的。

private static synchronized HttpDataSource.Factory getHttpDataSourceFactory( ) {if (sHttpDataSourceFactory == null) {CookieManager cookieManager = new CookieManager();cookieManager.setCookiePolicy(CookiePolicy.ACCEPT_ORIGINAL_SERVER);CookieHandler.setDefault(cookieManager);sHttpDataSourceFactory = new DefaultHttpDataSourceFactory("user-agent");}return sHttpDataSourceFactory;
}

在播放的时候需要先解密数据，使用 CryptoHttpDataSourceFactory，但是CryptoHttpDataSourceFactory 使用缓存后保存在缓存中的是解密后的数据，播放中导致数据无法识别。

CryptoWrapDataSource

那能不能在播放的时候送到播放器的数据解密但是下载保存的时候是原始数据呢。Exoplayer 的DataSource 设计使用了装饰模式，参考这个思路，在CacheDataSource 外面再装饰一层解密的CryptoWrapDataSource。这样Cache 缓存的时候是加密的数据，送到Exoplayer 的CryptoWrapDataSource 是解密以后的数据。

return new ProgressiveMediaSource.Factory(new CryptoWrapDataSource.Factory(buildCacheDataSourceFactory(cache)),.createMediaSource(uri);

文件分片大小

默认的分片大小为5M，CacheDataSink.DEFAULT_FRAGMENT_SIZE

在生成DownloadManager 的时候，传入自定义参数，CacheDataSinkFactory 定义分片大小。

DownloaderConstructorHelper downloaderConstructorHelper = new DownloaderConstructorHelper(getDownloadCache(context),getHttpDataSourceFactory(),null,new CacheDataSinkFactory(getDownloadCache(context),(sParameters != null && sParameters.mSegmentSize > 0) ? sParameters.mSegmentSize:CacheDataSink.DEFAULT_FRAGMENT_SIZE),null
);DefaultDownloaderFactory downloaderFactory = new DefaultDownloaderFactory(downloaderConstructorHelper);sDownloadManager = new DownloadManager(context,new DefaultDownloadIndex(getDatabaseProvider(context)),downloaderFactory);

下载网速的计算

在Exoplayer 的官方文档中对下载速度的需要通过DownloadManager 定期查询。DownloadService 支持Notification 通知，默认实现了一个 ForegroundNotificationUpdater 定期通知 Notification。

下载进度更新不会触发对DownloadManager.Listener. 要更新显示下载进度的 UI 组件，您应该DownloadManager以所需的更新速率定期查询。DownloadService 包含一个示例，它会定期更新服务前台通知。

参考这个实现实现我们的网速监听。

注册自定义的DownloadManagerListener

mDownloadManagerListener = new DownloadManagerListener(mHandlerListener);
CacheDownloadService.getDownloadManager(mContext).addListener(mDownloadManagerListener);

onDownloadChanged 中监听是否有下载开始，如果有下载开始，开始抛出消息计算网速。

private class DownloadManagerListener implements com.google.android.exoplayer2.offline.DownloadManager.Listener {private Handler mHandler;public DownloadManagerListener(Handler handler){mHandler = handler;}@Overridepublic void onInitialized(com.google.android.exoplayer2.offline.DownloadManager downloadManager) {mDownloadManager = downloadManager;initHandler();}@Overridepublic void onDownloadChanged(com.google.android.exoplayer2.offline.DownloadManager downloadManager, Download download) {if(mHandler != null){if (download.state == Download.STATE_DOWNLOADING) {Message message = Message.obtain();message.what = MSG_START;message.obj = download;if (download.contentLength > 0) {mHandler.sendMessage(message);}} else if (download.state == Download.STATE_COMPLETED) {Message message = Message.obtain();message.what = MSG_FINISH;message.obj = download;mHandler.sendMessage(message);}}}

initHandler() 中初始化一个线程用于处理消息和和计算网速

private void initHandler(){mHandlerThreadListener = new HandlerThread("DownloadManagerListener");mHandlerThreadListener.start();mHandlerListener = new Handler(mHandlerThreadListener.getLooper(), new Handler.Callback(){@Overridepublic boolean handleMessage(@NonNull Message msg) {switch (msg.what) {case MSG_START: {Download download = (Download) msg.obj;DownloadInfo downloadInfo = mHashDownloadInfo.get(download.request.id);if (downloadInfo == null) {downloadInfo = new DownloadInfo();downloadInfo.id = download.request.id;downloadInfo.updateTimeMs = download.startTimeMs;downloadInfo.bytesDownloaded = download.getBytesDownloaded();mHashDownloadInfo.put(downloadInfo.id, downloadInfo);}if (!mRunning) {mRunning = true;mHandlerListener.sendEmptyMessage(MSG_UPDATE);}}break;case MSG_UPDATE: {List<Download> downloadList = mDownloadManager.getCurrentDownloads();if (downloadList != null && downloadList.size() > 0) {long nowMs = Clock.DEFAULT.elapsedRealtime();for (Download dl : downloadList) {DownloadInfo downloadInfo = mHashDownloadInfo.get(dl.request.id);long speed = (dl.getBytesDownloaded() - downloadInfo.bytesDownloaded)/ ((nowMs - downloadInfo.updateTimeMs) / 1000);downloadInfo.updateTimeMs = nowMs;downloadInfo.bytesDownloaded = dl.getBytesDownloaded();for (NetworkSpeedListener li : sListener) {li.onProgress(dl, speed, dl.getPercentDownloaded());}}mHandlerListener.sendEmptyMessageDelayed(MSG_UPDATE, 1000);} else {mRunning = false;}}break;case MSG_FINISH:Download download = (Download) msg.obj;DownloadInfo downloadInfo = mHashDownloadInfo.get(download.request.id);long nowMs = Clock.DEFAULT.elapsedRealtime();long speed = (download.getBytesDownloaded() - downloadInfo.bytesDownloaded )/ (nowMs - downloadInfo.updateTimeMs);mHashDownloadInfo.remove(((Download) msg.obj).request.id);for (NetworkSpeedListener li : sListener) {li.onProgress((Download) msg.obj, speed, download.getPercentDownloaded());}break;}return false;}});
}

下载参数的设置 Builder 设计模式的使用

下载参数的设置使用了 Builder 设计模式

定义基类 ParametersBase

基类中定义各种属性
基类中定义 setXXX
默认构造函数ParametersBase(ParametersBase base) 这样变量的赋值操作都放在基类中操作，做到统一

class ParametersBase {protected long mMaxCacheSize = 512 * 1025 * 1025;protected long mSegmentSize = mMaxCacheSize;protected String mCachePath;protected int mMaxParallelDownloads;ParametersBase(ParametersBase base){this.mMaxCacheSize = base.mMaxCacheSize;this.mSegmentSize = base.mSegmentSize;this.mCachePath = base.mCachePath;this.mMaxParallelDownloads = base.mMaxParallelDownloads;}ParametersBase() {}......
}

Builder 类

Builder 类中增加 setXXX 函数
build 函数。 build 函数中直接使用基类构造函数生成 CacheDownloadParameters

public static class Builder extends ParametersBase{public Builder(){super();}public Builder(ParametersBase base) {super(base);}......public CacheDownloadParameters build(){CacheDownloadParameters parameters =  new CacheDownloadParameters(this);return parameters;}

CacheDownloadParameters

继承基类构造函数
buildUpon 函数使用基类构造函数生成

public class CacheDownloadParameters extends ParametersBase {private CacheDownloadParameters(ParametersBase base) {super(base);}public Builder buildUpon(){return new Builder(this);}
}