Java package file list

Java: List Files in a Directory

A lot of applications handle files in some way and file manipulation is one of the core knowledges in any programming language.

In order to manipulate files, we need to know where they’re located. Having an overview of files in a directory is paramount if we want to accomplish this, especially if we can perform operations on them through iteration. There are several ways to do this in Java, which we’ll show throughout this article.

For the sake of simplicity, all examples will be written for the following file tree:

Programming |-- minimax.c |-- super_hack.py |-- TODO.txt `-- CodingMusic |-- Girl Talk - All Day.mp3 |-- Celldweller - Frozen.mp3 |-- Lim Taylor - Isn't It Wonderful.mp3 `-- Radiohead - Everything in Its Right Place.mp3 

File.list()

The simplest method to list the names of files and folders in a given directory, without traversing the sub-directories, is the helper method .list() , which returns an array of String s.

We do this by using the .list() method on a File instance:

public class Pathnames < public static void main(String[] args) < // Creates an array in which we will store the names of files and directories String[] pathnames; // Creates a new File instance by converting the given pathname string // into an abstract pathname File f = new File("D:/Programming"); // Populates the array with names of files and directories pathnames = f.list(); // For each pathname in the pathnames array for (String pathname : pathnames) < // Print the names of files and directories System.out.println(pathname); > > > 

Using a simple for-each loop, we iterate through the array and print out the String s.

CodingMusic minimax.c super_hack.py TODO.txt 

Using this approach, all of the items in the CodingMusic directory aren’t shown, and a downside to this approach is that we can’t really do anything to the files themselves. We’re just getting their names. It’s useful when we just want to take a look at the files at face-value.

FilenameFilter

Another thing we can do with the .list() method is to create a FilenameFilter to return only the files we want:

File f = new File("D:/Programming"); // This filter will only include files ending with .py FilenameFilter filter = new FilenameFilter() < @Override public boolean accept(File f, String name) < return name.endsWith(".py"); > >; // This is how to apply the filter pathnames = f.list(filter); 

Running this piece of code would yield:

File.listFiles()

Similar to the previous method, this one can be used to return the names of files and directories, but this time we get them as an array of File objects, which gives us the ability to directly manipulate them:

public class Pathnames < public static void main(String args[]) < // try-catch block to handle exceptions try < File f = new File("D:/Programming"); FilenameFilter filter = new FilenameFilter() < @Override public boolean accept(File f, String name) < // We want to find only .c files return name.endsWith(".c"); > >; // Note that this time we are using a File class as an array, // instead of String File[] files = f.listFiles(filter); // Get the names of the files by using the .getName() method for (int i = 0; i < files.length; i++) < System.out.println(files[i].getName()); >> catch (Exception e) < System.err.println(e.getMessage()); >> > 

Now, let’s traverse deeper into the file system using recursion and some more methods to use on the File object:

public class ListFilesRecursively < public void listFiles(String startDir) < File dir = new File(startDir); File[] files = dir.listFiles(); if (files != null && files.length > 0) < for (File file : files) < // Check if the file is a directory if (file.isDirectory()) < // We will not print the directory name, just use it as a new // starting point to list files from listDirectory(file.getAbsolutePath()); > else < // We can use .length() to get the file size System.out.println(file.getName() + " (size in bytes: " + file.length()+")"); > > > > public static void main(String[] args) < ListFilesRecursively test = new ListFilesRecursively(); String startDir = ("D:/Programming"); test.listFiles(startDir); > > 

Girl Talk - All Day.mp3 (size in bytes: 8017524) Celldweller - Frozen.mp3 (size in bytes: 12651325) Lim Taylor - Isn't It Wonderful.mp3 (size in bytes: 6352489) Radiohead - Everything in Its Right Place.mp3 (size in bytes: 170876098) minimax.c (size in bytes: 20662) super_hack.py (size in bytes: 114401) TODO.txt (size in bytes: 998) 

Files.walk()

In Java 8 and later we can use the java.nio.file.Files class to populate a Stream and use that to go through files and directories, and at the same time recursively walk all subdirectories.

Note that in this example we will be using Lambda Expressions:

public class FilesWalk < public static void main(String[] args) < try (Stream walk = Files.walk(Paths.get("D:/Programming"))) < // We want to find only regular files List result = walk.filter(Files::isRegularFile) .map(x -> x.toString()).collect(Collectors.toList()); result.forEach(System.out::println); > catch (IOException e) < e.printStackTrace(); >> > 

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Here, we’ve populated a Stream using the .walk() method, passing a Paths argument. The Paths class consists of static methods that return a Path based on a String URI — and using a Path , we can locate the file easily.

The Path , Paths , Files , and many other classes belong to the java.nio package, which was introduced in Java 7 as a more modern way to represent files in a non-blocking way.

Then, using the Collections Framework, a list is generated.

Running this piece of code will yield:

D:\Programming\Coding Music\Radiohead - Everything in Its Right Place.mp3 D:\Programming\Coding Music\Lim Taylor - Isn't It Wonderful.mp3 D:\Programming\Coding Music\Celldweller - Frozen.mp3 D:\Programming\Coding Music\Girl Talk - All Day.mp3 D:\Programming\minimax.c D:\Programming\super_hack.py D:\Programming\TODO.txt 

Conclusion

Handling files in some way is a core task for most programming languages, and this includes the ability to list and find files in the file system. In order to manipulate files, we need to know where they’re located. Having an overview of files in a directory is paramount if we want to accomplish this, especially if we can perform operations on them through iteration.

In this article we showed a number of different ways in Java to list files on the file system, using both linear and recursive approaches.

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How to get list of all files/folders from a folder in Java?

The class named File of the java.io package represents a file or directory (path names) in the system. This class provides various methods to perform various operations on files/directories.

To get the list of all the existing files in a directory this class provides the files class provides list() (returns names) and ListFiles (returns File objects) with different variants.

The List() method

This method returns a String array which contains the names of all the files and directories in the path represented by the current (File) object.

Using this method, you can just print the names of the files and directories.

Example

The following Java program lists the names of all the files and directories in the path D:\ExampleDirectory.

import java.io.File; import java.io.IOException; public class ListOfFiles < public static void main(String args[]) throws IOException < //Creating a File object for directory File directoryPath = new File("D:\ExampleDirectory"); //List of all files and directories String contents[] = directoryPath.list(); System.out.println("List of files and directories in the specified directory:"); for(int i=0; i> >

Output

List of files and directories in the specified directory: SampleDirectory1 SampleDirectory2 SampleFile1.txt SampleFile2.txt SapmleFile3.txt

The ListFiles() method

This method returns an array holding the objects (abstract paths) of all the files (and directories) in the path represented by the current (File) object.

Since this method returns the objects of each file/directory in a folder. Using it you can access the properties of the files/directories such as size, path etc.

Example

The following Java program prints the name, path and, size of all the files in the path D:\ExampleDirectory.

import java.io.File; import java.io.IOException; public class ListOfFiles < public static void main(String args[]) throws IOException < //Creating a File object for directory File directoryPath = new File("D:\ExampleDirectory"); //List of all files and directories File filesList[] = directoryPath.listFiles(); System.out.println("List of files and directories in the specified directory:"); for(File file : filesList) < System.out.println("File name: "+file.getName()); System.out.println("File path: "+file.getAbsolutePath()); System.out.println("Size :"+file.getTotalSpace()); System.out.println(" "); >> >

Output

List of files and directories in the specified directory: File name: SampleDirectory1 File path: D:\ExampleDirectory\SampleDirectory1 Size :262538260480 File name: SampleDirectory2 File path: D:\ExampleDirectory\SampleDirectory2 Size :262538260480 File name: SampleFile1.txt File path: D:\ExampleDirectory\SampleFile1.txt Size :262538260480 File name: SampleFile2.txt File path: D:\ExampleDirectory\SampleFile2.txt Size :262538260480 File name: SapmleFile3.txt File path: D:\ExampleDirectory\SapmleFile3.txt Size :262538260480

The List(FilenameFilter filter) method

As suggested in its signature, this method accepts a FilenameFilter object and returns a String array containing the names of all the files and directories in the path represented by the current (File) object. But the retuned array contains the filenames which are filtered based on the specified filter.

Using this method, you can get the filtered names of the files and directories in a particular folder.

Example

The following Java program prints the names of the text files in the path D:\ExampleDirectory.

import java.io.File; import java.io.FilenameFilter; import java.io.IOException; public class ListOfFiles < public static void main(String args[]) throws IOException < //Creating a File object for directory File directoryPath = new File("D:\ExampleDirectory"); FilenameFilter textFilefilter = new FilenameFilter()< public boolean accept(File dir, String name) < String lowercaseName = name.toLowerCase(); if (lowercaseName.endsWith(".txt")) < return true; >else < return false; >> >; //List of all the text files String filesList[] = directoryPath.list(textFilefilter); System.out.println("List of the text files in the specified directory:"); for(String fileName : filesList) < System.out.println(fileName); >> >

Output

List of the text files in the specified directory −

SampleFile1.txt SampleFile2.txt SapmleFile3.txt

The ListFiles(FilenameFilter filter) method

This method accepts a FilenameFilter object and returns a File array containing the objects of all the files and directories in the path represented by the current File object. But the retuned array contains the files (objects) which are filtered based on their name

Using this method, you can get the filtered file objects of the files and directories in a particular folder, according to their names.

Example

The following Java program prints the name, path and, size of all the text files in the path D:\ExampleDirectory.

import java.io.File; import java.io.FilenameFilter; import java.io.IOException; public class ListOfFiles < public static void main(String args[]) throws IOException < //Creating a File object for directory File directoryPath = new File("D:\ExampleDirectory"); FilenameFilter textFilefilter = new FilenameFilter()< public boolean accept(File dir, String name) < String lowercaseName = name.toLowerCase(); if (lowercaseName.endsWith(".txt")) < return true; >else < return false; >> >; //List of all the text files File filesList[] = directoryPath.listFiles(textFilefilter); System.out.println("List of the text files in the specified directory:"); for(File file : filesList) < System.out.println("File name: "+file.getName()); System.out.println("File path: "+file.getAbsolutePath()); System.out.println("Size :"+file.getTotalSpace()); System.out.println(" "); >> >

Output

List of the text files in the specified directory: File name: SampleFile1.txt File path: D:\ExampleDirectory\SampleFile1.txt Size :262538260480 File name: SampleFile2.txt File path: D:\ExampleDirectory\SampleFile2.txt Size :262538260480 File name: SapmleFile3.txt File path: D:\ExampleDirectory\SapmleFile3.txt Size :262538260480

The ListFiles(FileFilter filter) method

This method accepts a FileFilter object and returns a File array containing the (File) objects of all the files and directories in the path represented by the current File object. But the retuned array contains the files (objects) which are filtered based on the property of the file.

Using this method, you can get the filtered file objects of the files and directories in a particular folder based on the size, path, type (file or, directory) etc…

Example

The following Java program prints the name, path and, size of all the files (not folders) in the path D:\ExampleDirectory.

import java.io.File; import java.io.FileFilter; import java.io.IOException; public class ListOfFiles < public static void main(String args[]) throws IOException < //Creating a File object for directory File directoryPath = new File("D:\ExampleDirectory"); FileFilter textFilefilter = new FileFilter()< public boolean accept(File file) < boolean isFile = file.isFile(); if (isFile) < return true; >else < return false; >> >; //List of all the text files File filesList[] = directoryPath.listFiles(textFilefilter); System.out.println("List of the text files in the specified directory:"); for(File file : filesList) < System.out.println("File name: "+file.getName()); System.out.println("File path: "+file.getAbsolutePath()); System.out.println("Size :"+file.getTotalSpace()); System.out.println(" "); >> >

Output

List of the text files in the specified directory: File name: cassandra_logo.jpg File path: D:\ExampleDirectory\cassandra_logo.jpg Size :262538260480 File name: cat.jpg File path: D:\ExampleDirectory\cat.jpg Size :262538260480 File name: coffeescript_logo.jpg File path: D:\ExampleDirectory\coffeescript_logo.jpg Size :262538260480 File name: javafx_logo.jpg File path: D:\ExampleDirectory\javafx_logo.jpg Size :262538260480 File name: SampleFile1.txt File path: D:\ExampleDirectory\SampleFile1.txt Size :262538260480 File name: SampleFile2.txt File path: D:\ExampleDirectory\SampleFile2.txt Size :262538260480 File name: SapmleFile3.txt File path: D:\ExampleDirectory\SapmleFile3.txt Size :262538260480

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