How to write to a file in Scala

Question

For reading  there is the useful abstraction Source  How can I write lines to a text file

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If you are anyways having Akka Streams in your project, it provides a one-liner:

def writeToFile(p: Path, s: String)(implicit mat: Materializer): Unit = {
  Source.single(ByteString(s)).runWith(FileIO.toPath(p))
}

Akka docs > Streaming File IO

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Here is a concise one-liner using the Scala compiler library   scala tools nsc io File  filename   writeAll  hello world     Alternatively  if you want to use the Java libraries you can do this hack   Some new PrintWriter  filename    foreach p   gt  p write  hello world    p close

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This is one of the features missing from standard Scala that I have found so useful that I add it to my personal library    You probably should have a personal library  too    The code goes like so   def printToFile f  java io File  op  java io PrintWriter   gt  Unit      val p   new java io PrintWriter f    try   op p    finally   p close         and it s used like this   import java io   val data   Array  Five   strings   in   a   file    printToFile new File  example txt      p   gt    data foreach p println

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This line helps to write a file from an Array or String    new PrintWriter outputPath    write ArrayName mkString       close

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A micro library I wrote  https   github com pathikrit better-files  file appendLine  Hello    World     or  file  lt  lt   Hello   lt  lt    n   lt  lt   World

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UPDATE on 2019 Sep 01    Starting with Scala 2 13  prefer using scala util Using Fixed bug where finally would swallow original Exception thrown by try if finally code threw an Exception     After reviewing all of these answers on how to easily write a file in Scala  and some of them are quite nice  I had three issues    In the Jus12 s answer  the use of currying for the using helper method is non-obvious for Scala FP beginners Needs to encapsulate lower level errors with scala util Try Needs to show Java developers new to Scala FP how to properly nest dependent resources so the close method is performed on each dependent resource in reverse order - Note  closing dependent resources in reverse order ESPECIALLY IN THE EVENT OF A FAILURE is a rarely understood requirement of the java lang AutoCloseable specification which tends to lead to very pernicious and difficult to find bugs and run time failures   Before starting  my goal isn t conciseness  It s to facilitate easier understanding for Scala FP beginners  typically those coming from Java  At the very end  I will pull all the bits together  and then increase the conciseness   First  the using method needs to be updated to use Try  again  conciseness is not the goal here   It will be renamed to tryUsingAutoCloseable   def tryUsingAutoCloseable A  lt   AutoCloseable  R     instantiateAutoCloseable       gt  A    parameter list 1    transfer  A   gt  scala util Try R      parameter list 2   scala util Try R      Try instantiateAutoCloseable         flatMap        autoCloseable   gt            var optionExceptionTry  Option Exception    None         try           transfer autoCloseable          catch             case exceptionTry  Exception   gt              optionExceptionTry   Some exceptionTry              throw exceptionTry                   finally           try             autoCloseable close             catch               case exceptionFinally  Exception   gt                optionExceptionTry match                   case Some exceptionTry    gt                    exceptionTry addSuppressed exceptionFinally                  case None   gt                    throw exceptionFinally                                             The beginning of the above tryUsingAutoCloseable method might be confusing because it appears to have two parameter lists instead of the customary single parameter list  This is called currying  And I won t go into detail how currying works or where it is occasionally useful  It turns out that for this particular problem space  it s the right tool for the job   Next  we need to create method  tryPrintToFile  which will create a  or overwrite an existing  File and write a List String   It uses a FileWriter which is encapsulated by a BufferedWriter which is in turn encapsulated by a PrintWriter  And to elevate performance  a default buffer size much larger than the default for BufferedWriter is defined  defaultBufferSize  and assigned the value 65536   Here s the code  and again  conciseness is not the goal here    val defaultBufferSize  Int   65536  def tryPrintToFile    lines  List String     location  java io File    bufferSize  Int   defaultBufferSize    scala util Try Unit        tryUsingAutoCloseable      gt  new java io FileWriter location       this open brace is the start of the second curried parameter to the tryUsingAutoCloseable method     fileWriter   gt        tryUsingAutoCloseable      gt  new java io BufferedWriter fileWriter  bufferSize       this open brace is the start of the second curried parameter to the tryUsingAutoCloseable method         bufferedWriter   gt            tryUsingAutoCloseable      gt  new java io PrintWriter bufferedWriter       this open brace is the start of the second curried parameter to the tryUsingAutoCloseable method             printWriter   gt                scala util Try                  lines foreach line   gt  printWriter println line                                               The above tryPrintToFile method is useful in that it takes a List String  as input and sends it to a File  Let s now create a tryWriteToFile method which takes a String and writes it to a File   Here s the code  and I ll let you guess conciseness s priority here    def tryWriteToFile    content  String    location  java io File    bufferSize  Int   defaultBufferSize    scala util Try Unit        tryUsingAutoCloseable      gt  new java io FileWriter location       this open brace is the start of the second curried parameter to the tryUsingAutoCloseable method     fileWriter   gt        tryUsingAutoCloseable      gt  new java io BufferedWriter fileWriter  bufferSize       this open brace is the start of the second curried parameter to the tryUsingAutoCloseable method         bufferedWriter   gt            Try bufferedWriter write content                   Finally  it is useful to be able to fetch the contents of a File as a String  While scala io Source provides a convenient method for easily obtaining the contents of a File  the close method must be used on the Source to release the underlying JVM and file system handles  If this isn t done  then the resource isn t released until the JVM GC  Garbage Collector  gets around to releasing the Source instance itself  And even then  there is only a weak JVM guarantee the finalize method will be called by the GC to close the resource  This means that it is the client s responsibility to explicitly call the close method  just the same as it is the responsibility of a client to tall close on an instance of java lang AutoCloseable  For this  we need a second definition of the using method which handles scala io Source   Here s the code for this  still not being concise    def tryUsingSource S  lt   scala io Source  R     instantiateSource       gt  S     transfer  S   gt  scala util Try R     scala util Try R      Try instantiateSource         flatMap        source   gt            var optionExceptionTry  Option Exception    None         try           transfer source          catch             case exceptionTry  Exception   gt              optionExceptionTry   Some exceptionTry              throw exceptionTry                   finally           try             source close             catch               case exceptionFinally  Exception   gt                optionExceptionTry match                   case Some exceptionTry    gt                    exceptionTry addSuppressed exceptionFinally                  case None   gt                    throw exceptionFinally                                             And here is an example usage of it in a super simple line streaming file reader  currently using to read tab-delimited files from database output    def tryProcessSource      file  java io File     parseLine   String  Int    gt  List String     line  index    gt  List line      filterLine   List String   Int    gt  Boolean    values  index    gt  true     retainValues   List String   Int    gt  List String     values  index    gt  values     isFirstLineNotHeader  Boolean   false    scala util Try List List String        tryUsingSource scala io Source fromFile file         source   gt        scala util Try            for                line  index   lt -               source getLines   buffered zipWithIndex             values                 parseLine line  index              if  index    0  amp  amp   isFirstLineNotHeader     filterLine values  index              retainedValues                 retainValues values  index              yield retainedValues           toList   must explicitly use toList due to the source close which will                    occur immediately following execution of this anonymous function               An updated version of the above function has been provided as an answer to a different but related StackOverflow question     Now  bringing that all together with the imports extracted  making it much easier to paste into Scala Worksheet present in both Eclipse ScalaIDE and IntelliJ Scala plugin to make it easy to dump output to the desktop to be more easily examined with a text editor   this is what the code looks like  with increased conciseness    import scala io Source import scala util Try import java io  BufferedWriter  FileWriter  File  PrintWriter   val defaultBufferSize  Int   65536  def tryUsingAutoCloseable A  lt   AutoCloseable  R     instantiateAutoCloseable       gt  A    parameter list 1    transfer  A   gt  scala util Try R      parameter list 2   scala util Try R      Try instantiateAutoCloseable         flatMap        autoCloseable   gt            var optionExceptionTry  Option Exception    None         try           transfer autoCloseable          catch             case exceptionTry  Exception   gt              optionExceptionTry   Some exceptionTry              throw exceptionTry                   finally           try             autoCloseable close             catch               case exceptionFinally  Exception   gt                optionExceptionTry match                   case Some exceptionTry    gt                    exceptionTry addSuppressed exceptionFinally                  case None   gt                    throw exceptionFinally                                            def tryUsingSource S  lt   scala io Source  R     instantiateSource       gt  S     transfer  S   gt  scala util Try R     scala util Try R      Try instantiateSource         flatMap        source   gt            var optionExceptionTry  Option Exception    None         try           transfer source          catch             case exceptionTry  Exception   gt              optionExceptionTry   Some exceptionTry              throw exceptionTry                   finally           try             source close             catch               case exceptionFinally  Exception   gt                optionExceptionTry match                   case Some exceptionTry    gt                    exceptionTry addSuppressed exceptionFinally                  case None   gt                    throw exceptionFinally                                            def tryPrintToFile    lines  List String     location  File    bufferSize  Int   defaultBufferSize    Try Unit      tryUsingAutoCloseable      gt  new FileWriter location     fileWriter   gt      tryUsingAutoCloseable      gt  new BufferedWriter fileWriter  bufferSize     bufferedWriter   gt        tryUsingAutoCloseable      gt  new PrintWriter bufferedWriter     printWriter   gt            Try lines foreach line   gt  printWriter println line                       def tryWriteToFile    content  String    location  File    bufferSize  Int   defaultBufferSize    Try Unit      tryUsingAutoCloseable      gt  new FileWriter location     fileWriter   gt      tryUsingAutoCloseable      gt  new BufferedWriter fileWriter  bufferSize     bufferedWriter   gt        Try bufferedWriter write content              def tryProcessSource      file  File    parseLine   String  Int    gt  List String     line  index    gt  List line     filterLine   List String   Int    gt  Boolean    values  index    gt  true    retainValues   List String   Int    gt  List String     values  index    gt  values    isFirstLineNotHeader  Boolean   false    Try List List String        tryUsingSource      gt  Source fromFile file     source   gt      Try          for              line  index   lt - source getLines   buffered zipWithIndex           values   parseLine line  index            if  index    0  amp  amp   isFirstLineNotHeader     filterLine values  index            retainedValues   retainValues values  index            yield retainedValues         toList             As a Scala FP newbie  I ve burned many hours  in mostly head-scratching frustration  earning the above knowledge and solutions  I hope this helps other Scala FP newbies get over this particular learning hump faster

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Unfortunately for the top answer  Scala-IO is dead  If you don t mind using a third-party dependency  consider using my OS-Lib library  This makes working with files  paths and the filesystem very easy      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      gt   hello      Perform filesystem operations os copy wd  file txt   wd  copied txt   os list wd     gt  Seq wd  copied txt   wd  file txt     It has one-liners for writing to files  appending to files  overwriting files  and many other useful common operations

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Giving another answer  because my edits of other answers where rejected     This is the most concise and simple answer  similar to Garret Hall s   File  filename   writeAll  hello world     This is similar to Jus12  but without the verbosity and with correct code style  def using A  lt    def close    Unit   B  resource  A  f  A   gt  B   B     try f resource  finally resource close    def writeToFile path  String  data  String   Unit      using new FileWriter path     write data    def appendToFile path  String  data  String   Unit     using new PrintWriter new FileWriter path  true      println data     Note you do NOT need the curly braces for try finally  nor lambdas  and note usage of placeholder syntax  Also note better naming

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No dependencies  with error handling   Uses methods from the standard library exclusively Creates directories for the file  if necessary Uses Either for error handling   Code  def write destinationFile  Path  fileContent  String   Either Exception  Path      write destinationFile  fileContent getBytes StandardCharsets UTF 8    def write destinationFile  Path  fileContent  Array Byte    Either Exception  Path      try       Files createDirectories destinationFile getParent         Return the path to the destinationFile if the write is successful     Right Files write destinationFile  fileContent       catch       case exception  Exception   gt  Left exception        Usage  val filePath   Paths get    testDir file txt    write filePath    A test   match     case Right pathToWrittenFile    gt  println s Successfully wrote to  pathToWrittenFile     case Left exception    gt  println s Could not write to  filePath  Exception   exception

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Edit 2019  8 years later   Scala-IO being not very active  if any  Li Haoyi suggests his own library lihaoyi os-lib  that he presents below   June 2019  Xavier Guihot mentions in his answer the library Using  a utility for performing automatic resource management     Edit  September 2011   since Eduardo Costa asks about Scala2 9  and since Rick-777 comments that scalax IO commit history is pretty much non-existent since mid-2009     Scala-IO has changed place  see its GitHub repo  from Jesse Eichar  also on SO       The Scala IO umbrella project consists of a few sub projects for different aspects and extensions of IO    There are two main components of Scala IO          Core - Core primarily deals with Reading and writing data to and from arbitrary sources and sinks  The corner stone traits are Input  Output and Seekable which provide the core API    Other classes of importance are Resource  ReadChars and WriteChars    File - File is a File  called Path  API that is based on a combination of Java 7 NIO filesystem and SBT PathFinder APIs    Path and FileSystem are the main entry points into the Scala IO File API       import scalax io    val output Output   Resource fromFile  someFile       Note  each write will open a new connection to file and           each write is executed at the begining of the file           so in this case the last write will be the contents of the file     See Seekable for append and patching files    Also See openOutput for performing several writes with a single connection  output writeIntsAsBytes 1 2 3  output write  hello   Codec UTF8  output writeStrings List  hello   world        Codec UTF8      Original answer  January 2011   with the old place for scala-io   If you don t want to wait for Scala2 9  you can use the scala-incubator   scala-io library   as mentioned in  Why doesn t Scala Source close the underlying InputStream     See the samples       several examples of writing data     import scalax io         FileOps  Path  Codec  OpenOption         the codec must be defined either as a parameter of ops methods or as an implicit     implicit val codec   scalax io Codec UTF8       val file  FileOps   Path   file           write bytes        By default the file write will replace        an existing file with the new data     file write  Array  1 2 3  map     toByte           another option for write is openOptions which allows the caller        to specify in detail how the write should take place        the openOptions parameter takes a collections of OpenOptions objects        which are filesystem specific in general but the standard options        are defined in the OpenOption object        in addition to the definition common collections are also defined        WriteAppend for example is a List Create  Append  Write      file write  List  1 2 3  map    toByte           write a string to the file     file write  Hello my dear file           with all options  these are the default options explicitely declared      file write  Hello my dear file   codec   Codec UTF8          Convert several strings to the file        same options apply as for write     file writeStrings   It costs      one      dollar     Nil          Now all options     file writeStrings  It costs      one      dollar     Nil                      separator     n     codec   Codec UTF8

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A simple answer   import java io File import java io PrintWriter  def writeToFile p  String  s  String   Unit         val pw   new PrintWriter new File p       try pw write s  finally pw close

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Starting Scala 2 13  the standard library provides a dedicated resource management utility  Using   It can be used in this case with resources such as PrintWriter or BufferedWriter which extends AutoCloseable in order to write to a file and  no matter what  close the resource afterwards    For instance  with java io api   import scala util Using  java io  PrintWriter  File      val lines   List  hello    world   Using new PrintWriter new File  file txt         writer   gt  lines foreach writer println     Or with java nio api   import scala util Using  java nio file  Files  Paths   java nio charset Charset     val lines   List  hello    world   Using Files newBufferedWriter Paths get  file txt    Charset forName  UTF-8         writer   gt  lines foreach line   gt  writer write line     n

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One liners for saving reading to from String  using java nio   import java nio file  Paths  Files  StandardOpenOption  import java nio charset  StandardCharsets  import scala collection JavaConverters    def write filePath String  contents String        Files write Paths get filePath   contents getBytes StandardCharsets UTF 8   StandardOpenOption CREATE     def read filePath String  String       Files readAllLines Paths get filePath   StandardCharsets UTF 8  asScala mkString     This isn t suitable for large files  but will do the job   Some links   java nio file Files write java lang String getBytes scala collection JavaConverters scala collection immutable List mkString

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Similar to the answer by Rex Kerr  but more generic  First I use a helper function          Used for reading writing to database  files  etc     Code From the book  Beginning Scala     http   www amazon com Beginning-Scala-David-Pollak dp 1430219890     def using A  lt    def close    Unit   B  param  A  f  A   gt  B   B   try   f param    finally   param close       Then I use this as   def writeToFile fileName String  data String       using  new FileWriter fileName         fileWriter   gt  fileWriter write data        and    def appendToFile fileName String  textData String      using  new FileWriter fileName  true         fileWriter   gt  using  new PrintWriter fileWriter           printWriter   gt  printWriter println textData              etc

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2019 Update    Summary - Java NIO  or NIO 2 for async  is still the most comprehensive file processing solution supported in Scala  The following code creates and writes some text to a new file   import java io  BufferedOutputStream  OutputStream  import java nio file  Files  Paths   val testFile1   Paths get  yourNewFile txt   val s1    text to insert in file  getBytes    val out1  OutputStream   new BufferedOutputStream    Files newOutputStream testFile1    try     out1 write s1  0  s1 length    catch     case     gt  println  Exception thrown during file writing     finally     out1 close        Import Java libraries  IO and NIO Create a Path object with your chosen file name  Convert your text that you want to insert into a file into a byte array Get your file as a stream  OutputStream  Pass your byte array into your output stream s write function Close the stream

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Similar to this answer  here is an example with fs2  version 1 0 4    import cats effect    import fs2   import fs2 io  import java nio file    import scala concurrent ExecutionContext import scala language higherKinds import cats syntax functor    object ScalaApp extends IOApp      def write T     p  Path  s  String                    implicit F  ConcurrentEffect T   cs  ContextShift T    T Unit          Stream s         covary T         through text utf8Encode         through          io file writeAll            p            scala concurrent ExecutionContext global            Seq StandardOpenOption CREATE                           compile        drain         def run args  List String    IO ExitCode           implicit val executionContext  ExecutionContext         scala concurrent ExecutionContext Implicits global      implicit val contextShift  ContextShift IO          IO contextShift executionContext       val outputFile  Path   Paths get  output txt        write IO  outputFile   Hello world n   as ExitCode Success

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To surpass samthebest and the contributors before him  I have improved the naming and conciseness     def using A  lt    def close     Unit   B  resource  A  f  A   gt  B   B       try f resource  finally resource close      def writeStringToFile file  File  data  String  appending  Boolean   false        using new FileWriter file  appending     write data

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Here s an example of writing some lines to a file using scalaz-stream   import scalaz   import scalaz stream    def writeLinesToFile lines  Seq String   file  String   Task Unit      Process lines                      Process that enumerates the lines      flatMap Process      n          Add a newline after each line      pipe text utf8Encode            Encode as UTF-8      to io fileChunkW fileName       Buffered write to the file      runLog Task  Unit               Get this computation as a Task      map     gt                         Discard the result  writeLinesToFile Seq  one    two     file txt   run

[scala] How to write to a file in Scala?

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