Scala file FAQ: How do I open and read files in Scala?
When you're writing Scala scripts, you often want to read text files. Fortunately it's pretty easy to openand read from a file in Scala. You can just use an approach like this:
import scala.io.Source
val filename = "fileopen.scala"
for (line <- Source.fromFile(filename).getLines()) {
println(line)
}
As you can see, this approach uses the scala.io.Source class. Within the for loop I can now access each line of the file using the 'line' object, and in this case I'm printing each line using println.
A variation of this is to add the mkString function to the file-reading portion of that code, like this:
val fileContents = Source.fromFile(filename).getLines.mkString
Another nice file-reading example comes from Bruce Eckel's website:
val fileLines = io.Source.fromFile("Colors.scala").getLines.toList
fileLines.foreach(println)As you can see from that example, you can read an entire text file into a Scala List with what appears to be only one line of source code.
Handling file exceptions
Of course you can generate exceptions when trying to open a file, and if you want to handle your exceptions, you use a syntax similar to the Java try/catch syntax, like this:
import scala.io.Source
val filename = "no-such-file.scala"
try {
for (line <- Source.fromFile(filename).getLines()) {
println(line)
}
} catch {
case ex: Exception => println("Bummer, an exception happened.")
}
If I change that Exception line to print my exception object, like this:
case ex: Exception => println(ex)
and then run this script again, I can see that this code throws a java.io.FileNotFoundException exception when it fails:
java.io.FileNotFoundException: no-such-file.scala (No such file or directory)
As a result, if I want to catch all the old Java exceptions like I used to, I can write a Scala script like this to catch the Java FileNotFoundException and IOException:
import scala.io.Source
import java.io.{FileReader, FileNotFoundException, IOException}
val filename = "no-such-file.scala"
try {
for (line <- Source.fromFile(filename).getLines()) {
println(line)
}
} catch {
case ex: FileNotFoundException => println("Couldn't find that file.")
case ex: IOException => println("Had an IOException trying to read that file")
}
