Java: Use parallel stream to copy files

Question

I am studying computer science at a University, and I have been assigned to create a 'normal' program, a program using implicit concurrency (parallel streams) and a program using explicit concurrency (threadpool)

I have created a batch file copier (source to destination) using the Java.NIO lib. I am trying to figure out how it would be possible to be done using parallel streams.

I have a String array which contains the file paths/names, and then I have this loop in order to copy the files to the destination:

int i = 0;
while (i < filelist.length){
    String filepath = filelist[i];
    Path source = Paths.get(filepath);
    Path target = Paths.get(FileBrowser.destinationpath+"/"+filenames[i]);  

    try {
        //replace existing file using java nio package
        System.out.println(Files.copy(source, target, StandardCopyOption.REPLACE_EXISTING));
    } catch (IOException e) {
        e.printStackTrace();
    }
    i++;
}

Any help on how to do this by using parallel streams would be appreciated.

PS. I know that copying files in parallel would not result in the files being copied faster rather than sequential, since it is not a CPU matter and more of a disk matter. Either way this assignment is to test and report results so that's why I have chosen this approach.

it could be faster if you have more than one disk. Also note that you would probably get better results with a parallel stream on Java 9 vs 8 because the performance has been improved: bugs.openjdk.java.net/browse/JDK-8072773 — assylias
– assylias, Commented Mar 18, 2016 at 17:07
@assylias thank you for the heads up, is what I am asking possible though? I can't seem to figure out how to apply that chunk of code as parallel stream. — Andreas Neophytou
– Andreas Neophytou, Commented Mar 18, 2016 at 18:02

Jaims · Accepted Answer · 2016-03-18 22:07:50Z

1

Using Java 8, you can iterate over any list as a parallel stream. So using your code, you could do something as the following:

Arrays.asList(filelist).parallelStream().forEach((filepath) -> {
    Path source = Paths.get(filepath);
    Path target = Paths.get(FileBrowser.destinationpath+"/"+filepath]);
    try {
        //replace existing file using java nio package
        System.out.println(Files.copy(source, target, StandardCopyOption.REPLACE_EXISTING));
    } catch (IOException e) {
        e.printStackTrace();
    }
});

answered Mar 18, 2016 at 22:07

Jaims

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2 Comments

Andreas Neophytou Over a year ago

thank you for your response, I can't use this: Path target = Paths.get(FileBrowser.destinationpath+"/"+filepath); I have a different string array for the filename, Path target = Paths.get(FileBrowser.destinationpath+"/"+filenames[i]);

Andreas Neophytou Over a year ago

I have modified your answer and it works :) I get better times copying files through this parallel stream too! Files: 85 Total Size: 440.57 MB NORMAL 38.79 35.98 36.24 PARALLEL 32.93 32.63 35.19 THREADPOOL 37.53 40.06 36.01

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