Scala: write string to file in one statement

问题:

For reading files in Scala, there is

Source.fromFile("file.txt").mkString 

Is there an equivalent and concise way to write a string to file?

Most languages support something like that. My favorite is Groovy:

def f = new File("file.txt") // Read def s = f.text // Write f.text = "file contents" 

I'd like to use the code for programs ranging from a single line to a short page of code. Having to use your own library doesn't make sense here. I expect a modern language to let me write something to a file conveniently.

There are posts similar to this, but they don't answer my exact question or are focused on older Scala versions.

For example:

• Read entire file in Scala?
• How to write to a file in Scala?

回答1:

A concise one line:

import java.io.PrintWriter new PrintWriter("filename") { write("file contents"); close } 

回答2:

It is strange that no one had suggested NIO.2 operations (available since Java 7):

import java.nio.file.{Paths, Files} import java.nio.charset.StandardCharsets  Files.write(Paths.get("file.txt"), "file contents".getBytes(StandardCharsets.UTF_8)) 

I think this is by far the simplest and easiest and most idiomatic way, and it does not need any dependencies sans Java itself.

回答3:

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 => p.write("hello world"); p.close} 

回答4:

If you like Groovy syntax, you can use the Pimp-My-Library design pattern to bring it to Scala:

import java.io._ import scala.io._  class RichFile( file: File ) {    def text = Source.fromFile( file )(Codec.UTF8).mkString    def text_=( s: String ) {     val out = new PrintWriter( file , "UTF-8")     try{ out.print( s ) }     finally{ out.close }   } }  object RichFile {    implicit def enrichFile( file: File ) = new RichFile( file )  } 

It will work as expected:

scala> import RichFile.enrichFile import RichFile.enrichFile  scala> val f = new File("/tmp/example.txt") f: java.io.File = /tmp/example.txt  scala> f.text = "hello world"  scala> f.text res1: String =  "hello world 

回答5:

import sys.process._ "echo hello world" #> new java.io.File("/tmp/example.txt") ! 

回答6:

You can easily use Apache File Utils. Look at function writeStringToFile. We use this library in our projects.

回答7:

A micro library I wrote: https://github.com/pathikrit/better-files

file.write("Hi!") 

or

file << "Hi!" 

回答8:

One also has this format, which is both concise and the underlying library is beautifully written (see the source code):

import scalax.io.Codec import scalax.io.JavaConverters._  implicit val codec = Codec.UTF8  new java.io.File("hi-file.txt").asOutput.write("I'm a hi file! ... Really!") 

回答9:

This is concise enough, I guess:

scala> import java.io._ import java.io._  scala> val w = new BufferedWriter(new FileWriter("output.txt")) w: java.io.BufferedWriter = java.io.BufferedWriter@44ba4f  scala> w.write("Alice\r\nBob\r\nCharlie\r\n")  scala> w.close() 

回答10:

You can do this with a mix of Java and Scala libraries. You will have full control over the character encoding. But unfortunately, the file handles will not be closed properly.

scala> import java.io.ByteArrayInputStream import java.io.ByteArrayInputStream  scala> import java.io.FileOutputStream import java.io.FileOutputStream  scala> BasicIO.transferFully(new ByteArrayInputStream("test".getBytes("UTF-8")), new FileOutputStream("test.txt")) 

回答11:

UPDATE: I have since created a more effective solution upon which I have elaborated here: https://stackoverflow.com/a/34277491/501113

I find myself working more and more in the Scala Worksheet within the Scala IDE for Eclipse (and I believe there is something equivalent in IntelliJ IDEA). Anyway, I need to be able to do a one-liner to output some of the contents as I get the "Output exceeds cutoff limit." message if I am doing anything significant, especially with the Scala collections.

I came up with a one-liner I insert into the top of each new Scala Worksheet to simplify this (and so I don't have to do the whole external library import exercise for a very simple need). If you are a stickler and notice that it is technically two lines, it's only to make it more readable in this forum. It is a single line in my Scala Worksheet.

def printToFile(content: String, location: String = "C:/Users/jtdoe/Desktop/WorkSheet.txt") =   Some(new java.io.PrintWriter(location)).foreach{f => try{f.write(content)}finally{f.close}} 

And the usage is simply:

printToFile("A fancy test string\ncontaining newlines\nOMG!\n") 

This allows me to optionally provide the file name should I want to have additional files beyond the default (which completely overwrites the file each time the method is called).

So, the second usage is simply:

printToFile("A fancy test string\ncontaining newlines\nOMG!\n", "C:/Users/jtdoe/Desktop/WorkSheet.txt") 

Enjoy!

回答12:

I know it's not one line, but it solves the safety issues as far as I can tell;

// This possibly creates a FileWriter, but maybe not val writer = Try(new FileWriter(new File("filename"))) // If it did, we use it to write the data and return it again // If it didn't we skip the map and print the exception and return the original, just in-case it was actually .write() that failed // Then we close the file writer.map(w => {w.write("data"); w}).recoverWith{case e => {e.printStackTrace(); writer}}.map(_.close) 

If you didn't care about the exception handling then you can write

writer.map(w => {w.writer("data"); w}).recoverWith{case _ => writer}.map(_.close) 

回答13:

Through the magic of the semicolon, you can make anything you like a one-liner.

import java.io.PrintWriter import java.nio.file.Files import java.nio.file.Paths import java.nio.charset.StandardCharsets import java.nio.file.StandardOpenOption val outfile = java.io.File.createTempFile("", "").getPath val outstream = new PrintWriter(Files.newBufferedWriter(Paths.get(outfile)   , StandardCharsets.UTF_8   , StandardOpenOption.WRITE)); outstream.println("content"); outstream.flush(); outstream.close() 

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