file merge logic: scala - scala

Question

For scala experts this might be a silly question but me as a beginner facing hard time to identify the solution. Any pointers would help.
I've set of 3 files in HDFS location by the names:
fileFirst.dat
fileSecond.dat
fileThird.dat
Not necessarily they'll be stored in any order. fileFirst.dat could be created at very last so a ls every time would show different ordering of the files.
My task is to combine all files in a single file in the order:
fileFirst contents, then fileSecond contents & finally fileThird contents; with newline as the separator, no spaces.
I tried some ideas but couldn't come up with something working. Every time the order of combination messes up.
Below is my function to merge whatever is coming in:
def writeFile(): Unit = {
val in: InputStream = fs.open(files(i).getPath)
try {
IOUtils.copyBytes(in, out, conf, false)
if (addString != null) out.write(addString.getBytes("UTF-8"))
} finally in.close()
}
Files is defined like this:
val files: Array[FileStatus] = fs.listStatus(srcPath)
This is part of a bigger function where I'm passing all the arguments used in this method. After everything is done, I'll do the out.close() to close the output stream.
Any ideas welcome, even if it goes against the file write logic I'm trying to do; just understand that I'm not that good in scala; for now :)

Answer 1

If you can enumerate your Paths directly, you don't really need to use listStatus. You could try something like this (untested):
val relativePaths = Array("fileFirst.dat", "fileSecond.dat", "fileThird.dat")
val paths = relativePaths.map(new Path(srcDirectory, _))
try {
val output = fs.create(destinationFile)
for (path <- paths) {
try {
val input = fs.open(path)
IOUtils.copyBytes(input, output, conf, false)
} catch {
case ex => throw ex // Feel free to do some error handling here
} finally {
input.close()
}
}
} catch {
case ex => throw ex // Feel free to do some error handling here
} finally {
output.close()
}