ExoPlayer的缓存三 SimpleCache的使用_exoplayer simplecache-优快云博客

本文链接：https://blog.youkuaiyun.com/chituhuan/article/details/125296214

ExoPlayer的缓存 – 三 Cache的使用

文章目录

CacheDataSource 读取数据

创建 CacheDataSource

和 exoplayer 的其他 DataSource 一样，CacheDataSource 的生成也是通过 Factory 模式生成，

  private CacheDataSource createDataSourceInternal(
      @Nullable DataSource upstreamDataSource, @Flags int flags, int upstreamPriority) {
   
    Cache cache = checkNotNull(this.cache);
    @Nullable DataSink cacheWriteDataSink;
    if (cacheIsReadOnly || upstreamDataSource == null) {
   
      cacheWriteDataSink = null;
    } else if (cacheWriteDataSinkFactory != null) {
   
      cacheWriteDataSink = cacheWriteDataSinkFactory.createDataSink();
    } else {
   
      cacheWriteDataSink = new CacheDataSink.Factory().setCache(cache).createDataSink();
    }
    return new CacheDataSource(
        cache,
        upstreamDataSource,
        cacheReadDataSourceFactory.createDataSource(),
        cacheWriteDataSink,
        cacheKeyFactory,
        flags,
        upstreamPriorityTaskManager,
        upstreamPriority,
        eventListener);
  }
}

CacheDataSource 构造函数的参数和读写有关的有

Cache cache 使用的缓存
@Nullable DataSource upstreamDataSource 根据url 生成的 DataSource, 可为null, 只能从Cache 中读取数据
cacheReadDataSource 从cache 中读取数据用的 DataSource
@Nullable DataSink cacheWriteDataSink 写缓存用的DataSink，可为null, 不可向Cache 中写数据
@Nullable CacheKeyFactory cacheKeyFactory 用来生成 Cache ID，用来匹配Cache

private CacheDataSource(
    Cache cache,
    @Nullable DataSource upstreamDataSource,
    DataSource cacheReadDataSource,
    @Nullable DataSink cacheWriteDataSink,
    @Nullable CacheKeyFactory cacheKeyFactory,
    ......
) {
   
  ......
      this.upstreamDataSource = upstreamDataSource;
      this.cacheWriteDataSource =
          cacheWriteDataSink != null
              ? new TeeDataSource(upstreamDataSource, cacheWriteDataSink)
              : null;
}

在 CacheDataSource 的构造函数中通过 upstreamDataSource 和cacheWriteDataSink 生成cacheWriteDataSource 类型为TeeDataSource。缓存的保存正是通过TeeDataSource 完成。

TeeDataSource 写入缓存数据

在TeeDataSource 的read 函数中，先从upstream 中读取数据，然后写入到dataSink 中。

public int read(byte[] buffer, int offset, int length) throws IOException {
   
  if (bytesRemaining == 0) {
   
    return C.RESULT_END_OF_INPUT;
  }
  int bytesRead = upstream.read(buffer