使用ExoPlayer库和OkHttp库，将视频缓存在本地进行播放，并在用户回到应用程序并重新聚焦时重新加载视频。具体的代码示例请参见以下代码：

1.在 build.gradle 中添加依赖：

implementation 'com.google.android.exoplayer:exoplayer:2.14.1'
implementation 'com.squareup.okhttp3:okhttp:4.9.1'

2.在您的活动或片段中实例化ExoPlayer：

private SimpleExoPlayer exoPlayer;
private Cache cache;

private void initializePlayer() {
    if (exoPlayer == null) {
        DefaultRenderersFactory renderersFactory = new DefaultRenderersFactory(this);
        DefaultTrackSelector trackSelector = new DefaultTrackSelector();
        DefaultLoadControl loadControl = new DefaultLoadControl.Builder()
                .setAllocator(new DefaultAllocator(true, C.DEFAULT_BUFFER_SEGMENT_SIZE))
                .setBufferDurationsMs(VideoRenderer.DEFAULT_MIN_BUFFER_MS, 60000, VideoRenderer.DEFAULT_BUFFER_FOR_PLAYBACK_MS, VideoRenderer.DEFAULT_BUFFER_FOR_PLAYBACK_AFTER_REBUFFER_MS)
                .setTargetBufferBytes(C.LENGTH_UNSET)
                .setPrioritizeTimeOverSizeThresholds(true)
                .createDefaultLoadControl();
        exoPlayer = new SimpleExoPlayer.Builder(this, renderersFactory)
                .setTrackSelector(trackSelector)
                .setLoadControl(loadControl)
                .build();

        String userAgent = Util.getUserAgent(this, "AppName");
        CacheKeyFactory cacheKeyFactory = new DefaultCacheKeyFactory();
        File cacheDirectory = new File(getCacheDir(), "exo-cache");
        cache = new SimpleCache(cacheDirectory, new NoOpCacheEvictor(), new ExoDatabaseProvider(this));
        CacheDataSource.Factory cacheDataSourceFactory = new CacheDataSource.Factory()
                .setCache(cache)
                .setUpstreamDataSourceFactory(new DefaultDataSourceFactory(this, userAgent))
                .setFlags(CacheDataSource.FLAG_IGNORE_CACHE_ON_ERROR)
                .setCacheKeyFactory(cacheKeyFactory);

        // Set cache data source for video URL
        MediaSource videoSource = new ProgressiveMediaSource.Factory(cacheDataSourceFactory).createMediaSource(mediaUrl);

        exoPlayer.setMediaSource(videoSource);
        exoPlayer.prepare();
        exoPlayer.setPlayWhenReady(true);
    }
}

3.实现 onPause() 方法并停止 ExoPlayer：

@Override
protected void onPause() {
    super.onPause();
    if (exoPlayer != null) {
        exoPlayer.setPlayWhenReady(false);
    }
}

4.实现 onResume() 方法并在 ExoPlayer 中恢复播放：

@Override
protected void onResume() {
    super.onResume();
    if (exoPlayer != null) {
        exoPlayer.setPlayWhenReady(true);
    }
}