How to delete the last line of the file in scala? - scala

Question

I am trying to append to a file such that I first want to delete the last line and then start appending. But, I can't figure how to delete the last line of the file.
I am appending the file as follows:
val fw = new FileWriter("src/file.txt", true) ;
fw.write("new item");
Can anybody please help me?
EDIT:
val lines_list = Source.fromFile("src/file.txt").getLines().toList
val new_lines = lines_list.dropRight(1)
val pw = new PrintWriter(new File("src/file.txt" ))
(t).foreach(pw.write) pw.write("\n")
pw.close()
After following your method, I am trying to write back to the file, but when I do this, all the contents, with the last line deleted come in a single line, however I want them to come in separate lines.

Answer 1

For very large files a simple solution relies in OS related tools, for instance sed (stream editor), and so consider a call like this,
import sys.process._
Seq("sed","-i","$ d","src/file1.txt")!
which will remove the last line of the text file. This approach is not so Scalish yet it solves the problem without leaving Scala.

Answer 2

Return random access file in position without last line.
import java.io.{RandomAccessFile, File}
def randomAccess(file: File) = {
val random = new RandomAccessFile(file, "rw")
val result = findLastLine(random, 0, 0)
random.seek(result)
random
}
def findLastLine(random: RandomAccessFile, position: Long, previous: Long): Long = {
val pointer = random.getFilePointer
if (random.readLine == null) {
previous
} else {
findLastLine(random, previous, pointer)
}
}
val file = new File("build.sbt")
val random = randomAccess(file)
And test:
val line = random.readLine()
logger.debug(s"$line")

Answer 3

My scala is way off, so people can probably give you a nicer solution:
import scala.io.Source
import java.io._
object Test00 {
def main(args: Array[String]) = {
val lines = Source.fromFile("src/file.txt").getLines().toList.dropRight(1)
val pw = new PrintWriter(new File("src/out.txt" ))
(lines :+ "another line").foreach(pw.println)
pw.close()
}
}
Sorry for the hardcoded appending, i used it just to test that everything worked fine.