How to recursively list all .rar files in a directory

Question

I want to list the .rar files in a folder and it subfolders till no folders are left.

This is the code I am currently using:

private String getFileNums(File file) {
        if (file.isDirectory()) {
            File[] list = file.listFiles(new FilenameFilter() {
                @Override
                public boolean accept(File file, String s) {
                    return s.toLowerCase().endsWith(".rar");
                }
            });
            int count = 0;
            if (list != null) {
                for (File f : list) {
                    if (f.isDirectory()) {
                        getFileNums(f);
                    } else {
                        count++;
                    }
                }
            }
            return  "Number of rar files in this folder and subfolders is " + count;
        } else {
            long length = file.length();
            return "File size in bytes is " + length;);
        }
    }

The problem I have with this code is that it doesn't list the .rar files in the subfolders, it only list those in the immediate folder.

For example say House is a folder that contains Bedroom (folder), Kitchen (folder), chair.rar (rar file) and door.rar (rar file). The above code only list chair.rar and door.rar , it doesn't list the rar files in Bedroom and Kitchen folders.

Please is there any where this can be fixed?

Answer 1

The problem is with your FilenameFilter . It's filtering out directories whose name does not end with ".rar" as well, which most directories don't. You need to make sure they pass the filter.

 new FilenameFilter() {
     @Override
     public boolean accept(File dir, String filename) {
         // create a file object to check whether we are looking at a directory.
         File f = new File(dir, filename); 
         return f.isDirectory() || filename.toLowerCase().endsWith(".rar");
     }
 }

After reading your comment, I realized that your code fails to "connect" the recursion.

int count = 0;

if (f.isDirectory()) {
    // Nothing comes out of the recursive call.
    // The result is completely lost
    getFileNums(f);
}

Also, you want to return int instead of String for a method that count the number of RAR files recursively.

private int getFileNums(File file) {
    if (file.isDirectory()) {
        File [] files = file.listFiles();
        if (files != null) {
            int count = 0;
            for (File f : files) {
                 if (f.isDirectory()) {
                     count += getFileNums(f);
                 } else if (f.getName().toLowerCase().endswith(".rar")) {
                     count++;
                 }
            }
            return count;
        } else {
            return 0;
        }
    } else {
        throw new IllegalArgumentException("Expecting a directory.");
    }
}

If you are using Java 8

You can use Files.walk .

import java.nio.file.*;

long numOfRar = Files.walk(file.toPath(), FileVisitOption.FOLLOW_LINKS)
                     .filter(p->p.toString().toLowerCase().endsWith(".rar"))
                     .count();

Answer 2

Sometimes it is easier to see things in Pseudocode. I think so, anyway.

processDirectory(thisDir)
  for each entry in thisDir
    if (entry is directory)
      processDirectory(entry)  // Recurse.
    else if (entry is .rar file)
      processRarFile(entry)
    endif
  endfor
end

Your code does not match that pattern, as Luke pointed out.