IO and parsing with idiomatic style?

28 replies

Tue, 2011-08-16, 00:54

Anthony Accioly 2

Joined: 2010-12-14,

Hi guys,

As a exercise yesterday I wrote a Simple Scala program to split srt
files (text based subtitles format) and readjust the intervals
accordingly. For that I resorted mostly to standard Java APIs and code
style (not proudly, just because these are the tools I know). In a lot
of places I couldn't find a way to get rid of the mutability.

If you guys could kindly help me rewrite the code in a more
idiomatic / functional way this would really help my studies. I'm
specially interested in learning Scala API and abstractions.
The only requirement is that I don't want to read the entire InputFile
into memory and make a big list (I could come up with something like
Source -> getLines -> mkString -> split -> map -> filter -> map), but
this wouldn't help me with real life big file parsing code.

So here it is:

case class Entry(id: Long, start: Date, end: Date, text: String) {

override def toString = {
// Anything better than StringBuilder with ok performance?
val sb = new StringBuilder;
sb.append(id)
sb.append("\n")
sb.append(timeFormat.format(start))
sb.append(" --> ")
sb.append(timeFormat.format(end))
sb.append(text)
sb.append("\n\n")

sb.toString()
}

}

object Main {

val timeFormat = new SimpleDateFormat("HH:mm:ss,SSS")
private val timePattern = Pattern.compile("\\d\\d:\\d\\d:\\d\\d,\\d\
\d\\d")
private val splitTime = Calendar.getInstance();
private var counter = 0; // How can I eliminate the mutable counter?

/**
* Parameters
*/
def main(args: Array[String]) {
val inputFile = new File(args(0))
val outputFile = new File(args(1))
splitTime.setTime(timeFormat.parse(args(2)))
val encoding = args(3);

val sc = new Scanner(inputFile, encoding)
val pw = new PrintWriter(outputFile, encoding)

sc.useDelimiter("\n\r\n");
// Any chance to get rid of the imperative style code without
// Having to read the entire file at once?
while (sc.hasNext) {
val line = sc.next()
val originalEntry = readEntry(line)
if (originalEntry.start.after(splitTime.getTime)) {
pw.print(buildEntryForSplittedFile(originalEntry))
}
}
sc.close() // Ok, I know about try and finally, this was pure
laziness
pw.close()
}

private def readEntry(string: String)= {
val sc = new Scanner(string)
sc.nextLine // Skip original id
val start = timeFormat.parse(sc.findInLine(timePattern))
val end = timeFormat.parse(sc.findInLine(timePattern))
sc.useDelimiter("\\Z")
val text = sc.next()

Entry(0, start, end, text)
}

private def buildEntryForSplittedFile (originalEntry: Entry) = {
val id = counter + 1;
counter = counter + 1;
val newStart = subtractTimes(originalEntry.start, splitTime)
val newEnd = subtractTimes(originalEntry.end, splitTime)

Entry(id, newStart, newEnd, originalEntry.text)
}

private def subtractTimes(t1 : Date, t2: Calendar) = {
// And again, can I ger rid of the mutable calls with resorting to
external libraries such as Joda-time?
val t3 = Calendar.getInstance()
t3.setTime(t1)
t3.add(Calendar.MILLISECOND, - t2.get(Calendar.MILLISECOND))
t3.add(Calendar.SECOND, - t2.get(Calendar.SECOND))
t3.add(Calendar.MINUTE, - t2.get(Calendar.MINUTE))
t3.add(Calendar.HOUR_OF_DAY, - t2.get(Calendar.HOUR_OF_DAY))

t3.getTime
}