In this recipe, we will be using a Java library from Apache named Commons IO. Throughout the book, we will be using version 2.5. Download the JAR file of your choice from here: https://commons.apache.org/proper/commons-io/download_io.cgi

Include the JAR file in your project an external JAR in Eclipse.

Create a method that takes the root directory in the hierarchy of directories as input:

        public void listFiles(String rootDir){ 

Create a file object with the root directory name:

        File dir = new File(rootDir); 

The FileUtils class of the Apache Commons library contains a method named listFiles(). Use this method to retrieve all the file names, and put the names in a list variable with <File> generics. Use TrueFileFilter.INSTANCE to match all directories:

        List<File> files = (List<File>) FileUtils.listFiles(dir,   
          TrueFileFilter.INSTANCE, TrueFileFilter.INSTANCE); 

The file names can be displayed on the standard output as follows. As we now have the names in a list, we have a means to process the data in these files further:

        for (File file : files) { 
           System.out.println("file: " + file.getAbsolutePath()); 
        } 

Close the method:

       } 

The method in this recipe, the class for it, and the driver method to run it are as follows:

import java.io.File; 
import java.util.List; 
import org.apache.commons.io.FileUtils; 
import org.apache.commons.io.filefilter.TrueFileFilter; 
 
public class FileListing{ 
   public static void main (String[] args){ 
      FileListing fileListing = new FileListing(); 
      fileListing.listFiles("Path for the root directory here"); 
   } 
   public void listFiles(String rootDir){ 
      File dir = new File(rootDir); 
 
      List<File> files = (List<File>) FileUtils.listFiles(dir,  
        TrueFileFilter.INSTANCE, TrueFileFilter.INSTANCE); 
      for (File file : files) { 
         System.out.println("file: " + file.getAbsolutePath()); 
      } 
   }