Scala script to copy files

Question

I want to copy file a.txt to newDir/ from within a scala script. In java this would be done by creating 2 file streams for the 2 files, reading into buffer from a.txt and writing it to the FileOutputStream of the new file. Is there a better way to achieve this in scala? May be something in scala.tools.nsc.io._. I searched around but could not find much.

Solution 1

For performance reasons it is better to use java.nio.Channel to do the copying.

Listing of copy.scala:

import java.io.{File,FileInputStream,FileOutputStream}
val src = new File(args(0))
val dest = new File(args(1))
new FileOutputStream(dest) getChannel() transferFrom(
    new FileInputStream(src) getChannel, 0, Long.MaxValue )

To try this out create a file called test.txt with the following content:

Hello World

After creating test.txt, run the following from the command line:

scala copy.scala test.txt test-copy.txt

Verify that test-copy.txt has Hello World as its content.

Solution 2

Why not use Apache Commons IO and FileUtils.copyFile() in particular ? Note that FileUtils has a large number of methods to copy files/directories etc.

Solution 3

Java 7 is now out and you have another option: java.nio.file.Files.copy. The probably easiest solution (And with Scalas superior import even easier). Provided that from and to are strings as in your question:

import java.nio.file.StandardCopyOption.REPLACE_EXISTING
import java.nio.file.Files.copy
import java.nio.file.Paths.get

implicit def toPath (filename: String) = get(filename)

copy (from, to, REPLACE_EXISTING)

Of course you should start using java.nio.file.Paths instead of strings.

Solution 4

If you really want to do it yourself instead of using a library like commons-io, you can do the following in version 2.8. Create a helper method "use". It will give you a form of automatic resource management.

def use[T <: { def close(): Unit }](closable: T)(block: T => Unit) {
  try {
    block(closable)
  }
  finally {
    closable.close()
  }
}

Then you can define a copy method like this:

import java.io._

@throws(classOf[IOException])
def copy(from: String, to: String) {
  use(new FileInputStream(from)) { in =>
    use(new FileOutputStream(to)) { out =>
      val buffer = new Array[Byte](1024)
      Iterator.continually(in.read(buffer))
          .takeWhile(_ != -1)
          .foreach { out.write(buffer, 0 , _) }
    }
  }
}

Note that the buffer size (here: 1024) might need some tuning.

Solution 5

Hire sbt.IO. It's pure scala, it can copy only changed files, has usefull routines like copyDirectory, delete, listFiles etc . You can use it as follow:

import sbt._
IO.copyFile(file1, file2)

Note you should add proper dependency:

libraryDependencies += "org.scala-sbt" % "io" % "0.13.0"

EDIT: Actually this is not a good approach since dependency "org.scala-sbt" % "io" % "version" was compiled using particular scala version and for now you cannot use it with 2.10.X scala version. But maybe in future you will can add double %% in you dependency like "org.scala-sbt" %% "io" % "version" and it will work...

View more solutions