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 reflect.io.file, this works with Scala 2.12:
reflect.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:
A micro library I wrote: https://github.com/pathikrit/better-files
file.write("Hi!")
or
file << "Hi!"
回答7:
You can easily use Apache File Utils. Look at function writeStringToFile. We use this library in our projects.
回答8:
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9:
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:
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12:
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()
来源：https://stackoverflow.com/questions/6879427/scala-write-string-to-file-in-one-statement