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Re: The first 10 files

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On 27.01.2013 03:43, Arne Vajhøj wrote:
> On 1/26/2013 9:35 PM, Arne Vajhøj wrote:
>> On 1/26/2013 9:02 PM, Arved Sandstrom wrote:

>> If OP happens to be on Java 7, then I will suggest using:
>>
>> java.nio.file.Files.newDirectoryStream(dir)
>>
>> It is a straight forward way of getting the first N files.
>>
>> And it is is as likely as the exception hack to not to read
>> all filenames from the OS.
>
> import java.io.IOException;
> import java.nio.file.Files;
> import java.nio.file.Path;
> import java.nio.file.Paths;
> import java.util.Iterator;
>
> public class ListFilesWithLimit {
>      public static void main(String[] args) throws IOException {
>          Iterator<Path> dir =
> Files.newDirectoryStream(Paths.get("/work")).iterator();
>          int n = 0;
>          while(dir.hasNext() && n < 10) {
>              System.out.println(dir.next());
>          }
>      }
> }

For earlier Java versions we could emulate that with a second thread.

package file;

import java.io.File;
import java.io.FileFilter;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.TimeUnit;

public final class ListFileTestThreaded2 {

   private static final class CountFilterThread extends Thread 
implements FileFilter {

     private final File dir;
     private final int maxFiles;
     private final BlockingQueue<List<File>> queue;
     private List<File> filesSeen = new ArrayList<File>();

     public CountFilterThread(File dir, int maxFiles, 
BlockingQueue<List<File>> queue) {
       this.dir = dir;
       this.maxFiles = maxFiles;
       this.queue = queue;
     }

     @Override
     public void run() {
       try {
         dir.listFiles(this);

         if (filesSeen != null) {
           send();
         }
       } catch (InterruptedException e) {
         e.printStackTrace();
       }
     }

     private void send() throws InterruptedException {
       queue.put(filesSeen);
       filesSeen = null;
     }

     @Override
     public boolean accept(final File f) {
       try {
         if (filesSeen != null) {
           filesSeen.add(f);

           if (filesSeen.size() == maxFiles) {
             send();
             assert filesSeen == null;
           }
         }

         return false;
       } catch (InterruptedException e) {
         throw new IllegalStateException(e);
       }
     }
   }

   private static final int[] LIMITS = { 10, 100, 1000, 10000, 
Integer.MAX_VALUE };

   public static void main(String[] args) throws InterruptedException {
     for (final String s : args) {
       System.out.println("Testing: " + s);
       final File dir = new File(s);

       if (dir.isDirectory()) {
         for (final int limit : LIMITS) {
           final SynchronousQueue<List<File>> queue = new 
SynchronousQueue<List<File>>();
           final CountFilterThread cf = new CountFilterThread(dir, 
limit, queue);
           cf.setDaemon(true);
           final long t1 = System.nanoTime();
           cf.start();
           final List<File> entries = queue.take();
           final long delta = System.nanoTime() - t1;
           System.out.printf("It took %20dus to retrieve %20d files, 
%20.5fus/file.\n",
               TimeUnit.NANOSECONDS.toMicros(delta), entries.size(), 
(double) TimeUnit.NANOSECONDS.toMicros(delta)
                   / entries.size());
         }
       } else {
         System.out.println("Not a directory.");
       }
     }

     System.out.println("done");
   }

}

https://gist.github.com/4648256

It's not guaranteed though that this will be faster.  And it's 
definitively not simpler than the straight forward approach. :-)

Cheers

	robert



-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

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Thread

The first 10 files Wojtek <nowhere@a.com> - 2013-01-26 01:14 -0800
  Re: The first 10 files Roedy Green <see_website@mindprod.com.invalid> - 2013-01-26 02:44 -0800
    Re: The first 10 files Lew <lewbloch@gmail.com> - 2013-01-26 10:20 -0800
  Re: The first 10 files "John B. Matthews" <nospam@nospam.invalid> - 2013-01-26 06:31 -0500
    Re: The first 10 files Wojtek <nowhere@a.com> - 2013-01-26 15:42 -0800
      Re: The first 10 files Jim Janney <jjanney@shell.xmission.com> - 2013-01-26 17:13 -0700
      Re: The first 10 files Arne Vajhøj <arne@vajhoej.dk> - 2013-01-26 21:21 -0500
      Re: The first 10 files "John B. Matthews" <nospam@nospam.invalid> - 2013-01-26 22:05 -0500
  Re: The first 10 files Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-01-26 08:24 -0400
    Re: The first 10 files Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-01-26 08:25 -0400
    Re: The first 10 files Arne Vajhøj <arne@vajhoej.dk> - 2013-01-26 13:26 -0500
      Re: The first 10 files Robert Klemme <shortcutter@googlemail.com> - 2013-01-26 22:15 +0100
        Re: The first 10 files Arne Vajhøj <arne@vajhoej.dk> - 2013-01-26 16:25 -0500
        Re: The first 10 files Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-01-26 17:06 -0500
          Re: The first 10 files Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2013-01-26 15:21 -0800
            Re: The first 10 files Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-01-26 20:42 -0500
              Re: The first 10 files Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2013-01-26 17:56 -0800
                Re: The first 10 files Arne Vajhøj <arne@vajhoej.dk> - 2013-01-26 21:29 -0500
                Re: The first 10 files Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-01-26 21:56 -0500
                Re: The first 10 files Jim Janney <jjanney@shell.xmission.com> - 2013-01-26 20:51 -0700
                Re: The first 10 files Jim Janney <jjanney@shell.xmission.com> - 2013-01-26 20:47 -0700
              Re: The first 10 files Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-01-26 22:02 -0400
                Re: The first 10 files Arne Vajhøj <arne@vajhoej.dk> - 2013-01-26 21:35 -0500
                Re: The first 10 files Arne Vajhøj <arne@vajhoej.dk> - 2013-01-26 21:43 -0500
                Re: The first 10 files Robert Klemme <shortcutter@googlemail.com> - 2013-01-27 13:55 +0100
                Re: The first 10 files Arne Vajhøj <arne@vajhoej.dk> - 2013-02-24 17:50 -0500
                Re: The first 10 files Robert Klemme <shortcutter@googlemail.com> - 2013-02-25 21:53 +0100
                Re: The first 10 files Jim Janney <jjanney@shell.xmission.com> - 2013-01-26 20:57 -0700
                Re: The first 10 files Wojtek <nowhere@a.com> - 2013-01-26 21:20 -0800
                Re: The first 10 files Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-01-27 07:23 -0400
                Re: The first 10 files Arne Vajhøj <arne@vajhoej.dk> - 2013-01-27 20:36 -0500
                Re: The first 10 files Wojtek <nowhere@a.com> - 2013-01-28 16:28 -0800
            Re: The first 10 files Arne Vajhøj <arne@vajhoej.dk> - 2013-01-26 21:23 -0500
            Re: The first 10 files Roedy Green <see_website@mindprod.com.invalid> - 2013-01-26 19:09 -0800
  Re: The first 10 files Jim Janney <jjanney@shell.xmission.com> - 2013-01-26 16:00 -0700
  Re: The first 10 files Knute Johnson <nospam@knutejohnson.com> - 2013-01-26 18:37 -0800
    Re: The first 10 files Wojtek <nowhere@a.com> - 2013-03-14 03:07 -0700
      Re: The first 10 files lipska the kat <"nospam at neversurrender dot co dot uk"> - 2013-03-14 12:49 +0000
      Re: The first 10 files Robert Klemme <shortcutter@googlemail.com> - 2013-03-15 11:38 +0100
        Re: The first 10 files Wojtek <nowhere@a.com> - 2013-03-15 10:31 -0700

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