Triggering on FileIO.toPath sink completion

问题

I have an IO Source I'm multiplexing a file and handing off to another part of the system to execute like:

source.alsoTo(FileIO.toPath(path))

This is used for a cache, i.e. i'm writing a file passing through my system to a temporary cache location. Once the cache is written, I want to move it atomically to its final location.

The consumer of the source gets a Future and knows when it is done, but my side-channel writing to file to disk has no such facility that I can find. Is there some way of attaching a completion handler to a sink so that I can complete my manipulation of that file?

回答1:

Instead of alsoTo, use alsoToMat and mapMaterializedValue to access the materialized value of the file Sink:

val source: Source[ByteString, _] = ???

val cachedSource =
  source
    .alsoToMat(FileIO.toPath(path))(Keep.right)
    .mapMaterializedValue { fileResult => // fileResult is a Future[IOResult]
      // do something with fileResult
    }

来源：https://stackoverflow.com/questions/53437098/triggering-on-fileio-topath-sink-completion