How to read a file as a byte array in Scala

Java 7:

import java.nio.file.{Files, Paths}

val byteArray = Files.readAllBytes(Paths.get("/path/to/file"))

I believe this is the simplest way possible. Just leveraging existing tools here. NIO.2 is wonderful.

This should work (Scala 2.8):

val bis = new BufferedInputStream(new FileInputStream(fileName))
val bArray = Stream.continually(bis.read).takeWhile(-1 !=).map(_.toByte).toArray

The library scala.io.Source is problematic, DON'T USE IT in reading binary files.

The error can be reproduced as instructed here: https://github.com/liufengyun/scala-bug

In the file data.bin, it contains the hexidecimal 0xea, which is 11101010 in binary and should be converted to 234 in decimal.

The main.scala file contain two ways to read the file:

import scala.io._
import java.io._

object Main {
  def main(args: Array[String]) {
    val ss = Source.fromFile("data.bin")
    println("Scala:" + ss.next.toInt)
    ss.close

    val bis = new BufferedInputStream(new FileInputStream("data.bin"))
    println("Java:" + bis.read)
    bis.close
  }
}

When I run scala main.scala, the program outputs follows:

Scala:205
Java:234

The Java library generates correct output, while the Scala library not.

val is = new FileInputStream(fileName)
val cnt = is.available
val bytes = Array.ofDim[Byte](cnt)
is.read(bytes)
is.close()

You might also consider using scalax.io:

scalax.io.Resource.fromFile(fileName).byteArray

You can use the Apache Commons Compress IOUtils

import org.apache.commons.compress.utils.IOUtils

val file = new File("data.bin")
IOUtils.toByteArray(new FileInputStream(file))

Asynchronous File reading using Scala Future and Java NIO2

  def readFile(path: Path)(implicit ec: ExecutionContext): Future[Array[Byte]] = {
    val p = Promise[Array[Byte]]()
    try {
      val channel = AsynchronousFileChannel.open(path, StandardOpenOption.READ)
      val buffer = ByteBuffer.allocate(channel.size().toInt);
      channel.read(buffer, 0L, buffer, onComplete(channel, p))
    }
    catch {
      case t: Exception => p.failure(t)
    }
    p.future
  }

  private def onComplete(channel: AsynchronousFileChannel, p: Promise[Array[Byte]]) = {
    new CompletionHandler[Integer, ByteBuffer]() {
      def completed(res: Integer, buffer: ByteBuffer): Unit = {
        p.complete(Try {
          buffer.array()
        })
      }

      def failed(t: Throwable, buffer: ByteBuffer): Unit = {
        p.failure(t)
      }
    }
  }

I have used below code to read a CSV file.

import scala.io.StdIn.readLine
import scala.io.Source.fromFile

readFile("C:/users/xxxx/Downloads/", "39025968_ccccc_1009.csv")

def readFile(loc :String,filenm :String): Unit ={

  var flnm = fromFile(s"$loc$filenm") // Imported fromFile package

  println("Files testing")
  /*for (line <- flnm.getLines()) {
    printf("%4d %s\n", line.length, line)
  }*/
  flnm.getLines().foreach(println) // getLines() is imported from readLines.
  flnm.close() 
}