Read entire file in Scala?

user_86684 0
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What's a simple and canonical way to read an entire file into memory in Scala? (Ideally, with control over character encoding.)

The best I can come up with is:

scala.io.Source.fromPath("file.txt").getLines.reduceLeft(_+_)

or am I supposed to use one of Java's god-awful idioms, the best of which (without using an external library) seems to be:

import java.util.Scanner
import java.io.File
new Scanner(new File("file.txt")).useDelimiter("\\Z").next()

From reading mailing list discussions, it's not clear to me that scala.io.Source is even supposed to be the canonical I/O library. I don't understand what its intended purpose is, exactly.

... I'd like something dead-simple and easy to remember. For example, in these languages it's very hard to forget the idiom ...

Ruby    open("file.txt").read
Ruby    File.read("file.txt")
Python  open("file.txt").read()
scala
19 Answers

Using getLines() on scala.io.Source discards what characters were used for line terminators (\n, \r, \r\n, etc.)

The following should preserve it character-for-character, and doesn't do excessive string concatenation (performance problems):

def fileToString(file: File, encoding: String) = {
  val inStream = new FileInputStream(file)
  val outStream = new ByteArrayOutputStream
  try {
    var reading = true
    while ( reading ) {
      inStream.read() match {
        case -1 => reading = false
        case c => outStream.write(c)
      }
    }
    outStream.flush()
  }
  finally {
    inStream.close()
  }
  new String(outStream.toByteArray(), encoding)
}
user_5518010

If you don't mind a third-party dependency, you should consider using my OS-Lib library. This makes reading/writing files and working with the filesystem very convenient:

// Make sure working directory exists and is empty
val wd = os.pwd/"out"/"splash"
os.remove.all(wd)
os.makeDir.all(wd)

// Read/write files
os.write(wd/"file.txt", "hello")
os.read(wd/"file.txt") ==> "hello"

// Perform filesystem operations
os.copy(wd/"file.txt", wd/"copied.txt")
os.list(wd) ==> Seq(wd/"copied.txt", wd/"file.txt")

with one-line helpers for reading bytes, reading chunks, reading lines, and many other useful/common operations

user_8712020

as a few people mentioned scala.io.Source is best to be avoided due to connection leaks.

Probably scalax and pure java libs like commons-io are the best options until the new incubator project (ie scala-io) gets merged.

user_2337810

You can use

Source.fromFile(fileName).getLines().mkString

however it should be noticed that getLines() removes all new line characters. If you want save formatting you should use

Source.fromFile(fileName).iter.mkString
user_94428980
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