Java program to fetch and sort files from a directory

Hi - Have you worked with Java file system objects? It has very good features like accessing files and sorting them in ascending order and descending order. In Java 1.5, Sun Microsystem has introduced the Comparator class to make the sort operations easier. So, I'm going to discuss about this today.

When you create a File object, it will just create a reference for the path that you've given for the constructor. You can invoke methods like exists() to find whether the file exists or isDirectory() to find whether this file represents a directory on the disk etc.

Here is the sample program to to access files and order them by ascending order based on name, last modified date, and size. It explains about file filter as well.

import java.io.File;
import java.io.FileFilter;
import java.util.Arrays;
import java.util.Comparator;

/**
 * A demo class to show the file sorting techniques.
 * @author Santhosh Reddy Mandadi
 * @since 05-Mar-2010
 * @version 1.0
 */
public class SortFiles
{
  public static void main(String[] args)
  {
    File dir = new File("C:\\");
    if(dir.isDirectory())
    {
      // Fetching the list from the directory
      File[] files = dir.listFiles();

      System.out.println("All the files including folders");
      System.out.println("--------------------------------");
      
      //Lists only files since we have applied file filter
      for(File file:files)
      {
        System.out.println(file.getName());
      }
   
   // Creating a filter to return only files.
      FileFilter fileFilter = new FileFilter()
      {
        @Override
        public boolean accept(File file) {
          return !file.isDirectory();
        }
      };
   
   files = dir.listFiles(fileFilter);
   
      System.out.println("\nAfter filtering the folders");
      System.out.println("--------------------------------");

      // Sort files by name
      Arrays.sort(files, new Comparator()
      {
        @Override
        public int compare(Object f1, Object f2) {
          return ((File) f1).getName().compareTo(((File) f2).getName());
        }
      });

      //Prints the files in file name ascending order
      for(File file:files)
      {
        System.out.println(file.getName());
      }
      System.out.println("\nAfter sorting by name");
      System.out.println("----------------------------------");

      // Sort files by size.
      Arrays.sort(files, new Comparator()
      {
        @Override
        public int compare(Object f1, Object f2)
        {
          if (((File) f1).length() < ((File) f2).length())
          {
            return -1;
          }
          else if (((File) f1).length() > ((File) f2).length())
          {
            return 1;
          }
          else
          {
            return 0;
          }
        }
      });

      //Prints files in order by file size
      for(File file:files)
      {
        System.out.println(file.getName());
      }
      System.out.println("\nAfter sorting by length");
      System.out.println("-------------------------------");

      // Sort files by date.
      Arrays.sort(files, new Comparator()
      {
        @Override
        public int compare(Object f1, Object f2)
        {
          if (((File) f1).lastModified() < ((File) f2).lastModified())
          {
            return -1;
          }
          else if (((File) f1).lastModified() > ((File) f2).lastModified())
          {
            return 1;
          }
          else
          {
            return 0;
          }
        }
      });

      //Prints files in order by last modified date
      for(File file:files)
      {
        System.out.println(file.getName());
      }
      System.out.println("-------------------------");
    }
  }
}

E:\Java>java SortFiles
All the files including folders
--------------------------------
$AVG
$Recycle.Bin
autoexec.bat
bootmgr
BOOTNXT
config.sys
cygwin
Documents and Settings
hiberfil.sys
Intel
MSOCache
oracle
pagefile.sys
Pdfedit
PerfLogs
Program Files
ProgramData
swapfile.sys
System Volume Information
TurboC++
Users
Windows
Windows Activation Technologies

After filtering the folders
--------------------------------
BOOTNXT
autoexec.bat
bootmgr
config.sys
hiberfil.sys
pagefile.sys
swapfile.sys

After sorting by name
----------------------------------
BOOTNXT
config.sys
autoexec.bat
bootmgr
swapfile.sys
pagefile.sys
hiberfil.sys

After sorting by length
-------------------------------
swapfile.sys
pagefile.sys
hiberfil.sys
BOOTNXT
bootmgr
config.sys
autoexec.bat
-------------------------

Above program has been tested in 1.5 and 1.6.

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