Scala: How to write text files (PrintWriter, FileWriter, BufferedWriter, and File)

By Alvin Alexander. Last updated: July 30, 2024

This is an excerpt from the 1st Edition of the Scala Cookbook (partially modified for the internet). This is Recipe 12.2, “How to write text files in Scala.”

Problem

You want to write plain text to a file in Scala, such as a simple configuration file, text data file, or other plain-text document.

Solution

Scala doesn’t offer any special file-writing capability, so fall back and use the Java PrintWriter or FileWriter approaches:

// PrintWriter
import java.io._
val pw = new PrintWriter(new File("hello.txt" ))
pw.write("Hello, world")
pw.close

// FileWriter
val file = new File(canonicalFilename)
val bw = new BufferedWriter(new FileWriter(file))
bw.write(text)
bw.close()

Note that you’ll generally want to add a newline character (\n) to each line you print with these approaches; If you don’t, you’ll get one long line of output.

Note that a better solution is shown below that uses the scala.util.Using control structure.

Discussion

Although I normally use a FileWriter to write plain text to a file, a good post at coderanch.com describes some of the differences between PrintWriter and FileWriter. For instance, while both classes extend from Writer, and both can be used for writing plain text to files, FileWriter throws IOExceptions, whereas PrintWriter does not throw exceptions, and instead sets Boolean flags that can be checked. There are a few other differences between the classes; check their Javadoc for more information.

Update: See the Comments section below for a note about explicitly declaring the charset when using PrintWriter. Note that PrintWriter constructors let you specify the charset, but FileWriter does not. The Java 8 FileWriter Javadoc suggests that you use an OutputStreamWriter on a FileOutputStream to specify the file encoding.

Example Scala file-writing methods

As an example of how to use these file-writing methods, here are two writeFile methods from my little Scala file utilities project:

import java.io._ 

/**
 * write a `Seq[String]` to the `filename`.
 * note: does not handle exceptions.
 */
def writeFile(filename: String, lines: Seq[String]): Unit = {
    val file = new File(filename)
    val bw = new BufferedWriter(new FileWriter(file))
    for (line <- lines) {
        bw.write(line)
    }
    bw.close()
}

/**
 * write a `String` to the `filename`.
 * note: does not handle exceptions.
 */
def writeFile(filename: String, s: String): Unit = {
    val file = new File(filename)
    val bw = new BufferedWriter(new FileWriter(file))
    bw.write(s)
    bw.close()
}

Note that those methods don’t handle exceptions, but you can use them as the start of your own methods, if you’d like.

Update: Writing to a file with scala.util.Using

As a brief update, if you want to write to a file using Scala and scala.util.Using, I believe this function is correct:

def writeFile(filename: String, content: String): Try[Unit] =
    Using(BufferedWriter(FileWriter( File(filename), false))) { bufferedWriter =>
        bufferedWriter.write(content)
    }

In a related note, you can also read from a file using scala.util.Using like this:

def readFile(filename: String): Try[String] =
    Using(BufferedReader(FileReader(filename))) { reader =>
        val rez = Iterator.continually(reader.readLine()).takeWhile(_ != null)
        rez.mkString("\n")
    }

If you ever wanted to use scala.util.Using to write to a file or read from a file, I hope this is helpful.