Scala-IO Getting Started

For the next several posts you will need to have Scala-IO installed and probably should have a sbt project as well.

There are currently 2 Scala-IO 0.4 releases.

• Scala-io 0.4-seq - A version of Scala 0.4 without the Akka dependency and therefore no ASync support
• Scala-io 0.4 - The full version that contains an Akka  dependency

The Scala 2.10 versions will have no Akka dependency but can optionally use Akka.

So getting started:

Download the example project on the docs website (http://jesseeichar.github.com/scala-io-doc/latest):

• Go to Getting Started and follow instructions for downloading and running the example project.  The following goes through the steps for the 0.4.1 instructions.

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sbt console   scala> import scalax.io._ import scalax.io._   scala> import java.net.URL import java.net.URL   scala> Resource.fromURL(new URL("http://www.scala-lang.com")).      | lines().async.size.onComplete(println) res3: akka.dispatch.Future[Int] = akka.dispatch.DefaultPromise@363adfb4   scala> Right(770)

The last line (Right(770)) is not a command to enter; it is the result of the asynchonous call.

Introducing Scala-IO

This is the start of a series of posts on Scala-IO.  Scala-IO is as the name implies a library for performing input and output operations with Scala.  There are 4 main facets to the library

• Basic IO - Reading and writing to some underlying resource.  The current implementation is Java based and thus allows reading and writing to resources like java.io.Readers, Writers, Channels, Streams, etc...
• File API - A library loosely designed after java 7 nio.file API with an additional simple unix like DSL for traversing and searching the filesystem.  It is a pluggable architecture which allows plugins for systems like WebDav or Zip filesystems to be addressed in a similar manner as the local filesystem.  The included implementation is for the local file system and is implemented on the java.io APIs
• Asynchronous Access - Throughout the APIs are both synchronous and asynchronous options allowing both models of programming to be easily used.  
• In the 2.10.x + versions the future implementations are pluggable but require no additional libraries if so that is the desire
• In 2.9.x versions there are two different dependencies one with asynchronous APIs implemented on Akka and one without any asynchronous APIs
• Processor API - An API for defining complex IO processes declaratively.

This series will look at normally a small and simple IO operation each day (or so) rather than only a few in-depth articles.  This is required because of my limited available time.

With the introduction done lets look at two small examples:

Read File with Core API (not File API):

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import scalax.io._   // Create a resource from a file.  This is a convenience method and the string can be // a relative path or a absolute path.  While this is convenient it is not portable // so it is recommened to use the File API to create a Path object and read from that val input:Input = Resource.fromFile("someFile")   // read all bytes into an in memory array input.byteArray   // skip first 5 bytes and take the next 5 // force the operation to take place. // The bytes is a ResourceView which is a LongTraversableView, // meaning it will evaluate lazily until the data is forced // or requested input.bytes.drop(5).take(5).force   // read all bytes into a string // note: codec can be passed implicitely as well input.string(Codec.UTF8)

Same thing but with File API:

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import scalax.file.Path   val path = Path("file")   // read all bytes into an in memory array path.byteArray   // skip first 5 bytes and take the next 5 // force the operation to take place. // The bytes is a ResourceView which is a LongTraversableView, // meaning it will evaluate lazily until the data is forced // or requested path.bytes.drop(5).take(5).force   // read all bytes into a string // note: codec can be passed implicitly as well path.string(Codec.UTF8)