使用ExoPlayer库实现视频缓存和加载。首先需要添加ExoPlayer库依赖。然后创建带有缓存的ExoPlayer实例，指定缓存大小和位置。只有在应用程序处于焦点状态时才重新加载视频。可以使用LifecycleObserver或FragmentLifecycleCallbacks来实现此目的。

以下是缓存和重新加载视频的示例代码：

1. 添加ExoPlayer库依赖：

implementation 'com.google.android.exoplayer:exoplayer:2.14.1'

2. 创建带有缓存的ExoPlayer实例：

SimpleCache simpleCache = new SimpleCache(context.getCacheDir(), new LeastRecentlyUsedCacheEvictor(1024 * 1024 * 100)); CacheDataSourceFactory cacheDataSourceFactory = new CacheDataSourceFactory(simpleCache, new DefaultHttpDataSourceFactory(userAgent), CacheDataSource.FLAG_IGNORE_CACHE_ON_ERROR); MediaSource mediaSource = new ProgressiveMediaSource.Factory(cacheDataSourceFactory).createMediaSource(videoUri); SimpleExoPlayer exoPlayer = new SimpleExoPlayer.Builder(context).setMediaSource(mediaSource).build();

3. 实现LifecycleObserver或FragmentLifecycleCallbacks以仅在应用程序处于焦点状态时重新加载视频：

@OnLifecycleEvent(Lifecycle.Event.ON_RESUME) public void onResume() { exoPlayer.setPlayWhenReady(true); }

@OnLifecycleEvent(Lifecycle.Event.ON_PAUSE) public void onPause() { exoPlayer.setPlayWhenReady(false); }