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.

Answer 1

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.

Answer 2

If you don't wanna use anything external, just do it as you would have done it in Java. The nice thing, is that you can.

Answer 3

If you don't care too much about speed, you can make your life slightly easier by reading the file using scala.io.Source (this implementation is for 2.7.7):

def copyF(from: java.io.File, to: String) {
  val out = new java.io.BufferedWriter( new java.io.FileWriter(to) );
  io.Source.fromFile(from).getLines.foreach(s => out.write(s,0,s.length));
  out.close()
}

But Source goes to all the trouble of parsing the file line by line, and then you just write it out again without actually processing the lines. Using byte read/write Java style will be considerably faster (about 2-3x last time I benchmarked it).

Answer 4

Scalax has scalax.io.FileExtras.copyTo(dest : File). But developement seems to have stopped.

Answer 5

Runtime.getRuntime.exec("cp 01.txt 02.txt", Array(): Array[String], new java.io.File(".")).waitFor

Only works on real operating systems. :D

Answer 6

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.

Answer 7

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(src) getChannel() transferFrom(
    new FileInputStream(dest) 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.