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About Ilias Koutsakis

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Ilias has graduated from the Department of Informatics and Telecommunications of the National and Kapodistrian University of Athens. He is interested in all aspects of software engineering, particularly data mining, and loves the challenge of working with new technologies. He is pursuing the dream of clean and readable code on a daily basis.

org.apache.commons.io.FileUtils Example

In this example we are going to show some of the capabilities of the FileUtils class, which is a part of Apache Commons IO. The methods implemented in this class are all about file manipulation, and in many cases they make a developer’s life much easier. The main reason that this and other classes in Apache Commons exist, is that their methods are wrappers for very usual tasks, so the boilerplate code is immediately smaller and the program as a whole cleaner and more understandable.



1. FileUtils Methods

We will explain the most important methods found inside the FileUtils class, and then we are going to show how to actually use them. FileUtils is a static class, which means that we don’t instatiate it, but we are using the class name and the appropriate method instead, like this: FileUtils.method().

  • contentEquals(File file1, File file2): It compares the contents of 2 File objects, and returns whether they are the same or not.
  • copyDirectory(File source, File destination): It copies a whole directory (source) to another (destination). Bothe need to be opened in Java as file objects.
  • copyDirectory(File source, File destination, FileFilter filter): Same as above, but in this case we can filter the contents of a directory by applying specific file filters (checking for names, modification dates, etc).
  • copyFile(File srcFile, File destFile): Copies a file to another file.
  • deleteDirectory(File directory): Deletes a directory recursively.
  • getTempDirectory(): Returns a File object that represents the system temporary directory.
  • getUserDirectory(): Same as above, but this time representing the user directory.
  • lineIterator(File file): It creates an iterator that can iterate over the lines of a given File.
  • sizeOfDirectory(File directory): It returns the size of a directory including its contents.
  • write(File file, CharSequence data): Writes a CharSequence in a file, using the specified enoding.
  • writeLines(File file, Collection<?> lines): Writes the collection of lines to a File.

So, let’s see how these methods are used in action!

2. FileUtils Example


import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;

import org.apache.commons.io.FileUtils;
import org.apache.commons.io.LineIterator;
import org.apache.commons.io.filefilter.SuffixFileFilter;

public class FileUtilsExample {
    private static final String MAIN_PATH = "C:\\Users\\Lilykos\\Desktop\\FUExFiles\\";

    public static void main(String[] args) throws IOException {
        // file1: "Hello World!"
        // file2: "Hello World!!!"
        File file1 = FileUtils.getFile(MAIN_PATH + "cmpFile1.txt");
        File file2 = FileUtils.getFile(MAIN_PATH + "cmpFile2.txt");
        System.out.println("Are cmpFile1 and cmpFile2 equal: " +
                FileUtils.contentEquals(file1, file2));
        // We can copy a whole path somewhere
        // and check if the operation was successful.
                FileUtils.getFile(MAIN_PATH),                   // source
                FileUtils.getFile(MAIN_PATH + "copiedPath\\")); // destination
        System.out.println("Does the copiedPath exist: " +
                FileUtils.getFile(MAIN_PATH + "copiedPath\\").exists());
        // Copy a directory by filtering out all the txt files.
        // In the directory right now: cmpFile1.txt, cmpFile2.txt, zipFile.zip
                FileUtils.getFile(MAIN_PATH + "copiedFilterPath\\"),
                new SuffixFileFilter(".zip"));
        for (File f: FileUtils.getFile(MAIN_PATH + "copiedFilterPath\\").listFiles()) {
            System.out.println("Contents of copiedFilterPath: " + f.getName());
        // Copy a file
        File copy = FileUtils.getFile(MAIN_PATH + "copyOfFile1.txt");
        FileUtils.copyFile(file1, copy);
        System.out.println("Are cmpFile1 and copyOfFile1 equal: " +
                FileUtils.contentEquals(file1, copy));
        // Right now there are these files in the MAIN_PATH.
        for (File f: FileUtils.getFile(MAIN_PATH).listFiles()) {
            System.out.println("Contents of MAIN_PATH: " + f.getName());
        // Let's delete a directory and see the results.
        FileUtils.deleteDirectory(FileUtils.getFile(MAIN_PATH + "copiedFilterPath\\"));
        for (File f: FileUtils.getFile(MAIN_PATH).listFiles()) {
            System.out.println("Contents of MAIN_PATH after deletion: " + f.getName());
        // Directories
        System.out.println("Temp Dir: " +
        System.out.println("User Dir: " +
        // Line Iterator
        LineIterator iter = FileUtils.lineIterator(file1);
        while (iter.hasNext()) {
            System.out.println("cmpFile1 lines: " + iter.next());
        // Directory size
        System.out.println("Size of dir: " +
                FileUtils.sizeOfDirectory(FileUtils.getFile(MAIN_PATH)) +
                " bytes.");
        // Ways of writing lines to a file.
        File fileToWrite1 = FileUtils.getFile(MAIN_PATH + "fileToWrite1.txt");
        File fileToWrite2 = FileUtils.getFile(MAIN_PATH + "fileToWrite2.txt");
        Collection lines = new ArrayList<>();
        lines.add("Written with FileUtils!");
        lines.add("For Java Code Geeks.");
        FileUtils.write(fileToWrite1, "Written with FileUtils!");
        FileUtils.writeLines(fileToWrite2, lines);
        iter = FileUtils.lineIterator(fileToWrite1);
        while (iter.hasNext()) {
            System.out.println("fileToWrite1 lines: " + iter.next());
        iter = FileUtils.lineIterator(fileToWrite2);
        while (iter.hasNext()) {
            System.out.println("fileToWrite2 lines: " + iter.next());


Are cmpFile1 and cmpFile2 equal: false
Does the copiedPath exist: true
Contents of copiedFilterPath: zipFile.zip
Are cmpFile1 and copyOfFile1 equal: true
Contents of MAIN_PATH: cmpFile1.txt
Contents of MAIN_PATH: cmpFile2.txt
Contents of MAIN_PATH: copiedFilterPath
Contents of MAIN_PATH: copiedPath
Contents of MAIN_PATH: copyOfFile1.txt
Contents of MAIN_PATH: fileToWrite1.txt
Contents of MAIN_PATH: fileToWrite2.txt
Contents of MAIN_PATH: zipFile.zip
Contents of MAIN_PATH after deletion: cmpFile1.txt
Contents of MAIN_PATH after deletion: cmpFile2.txt
Contents of MAIN_PATH after deletion: copiedPath
Contents of MAIN_PATH after deletion: copyOfFile1.txt
Contents of MAIN_PATH after deletion: fileToWrite1.txt
Contents of MAIN_PATH after deletion: fileToWrite2.txt
Contents of MAIN_PATH after deletion: zipFile.zip
Temp Dir: C:\Users\Lilykos\AppData\Local\Temp
User Dir: C:\Users\Lilykos
cmpFile1 lines: Hello World!
Size of dir: 304 bytes.
fileToWrite1 lines: Written with FileUtils!
fileToWrite2 lines: Written with FileUtils!
fileToWrite2 lines: For Java Code Geeks.

3. Download the example

This was an example of FileUtils in Apache Commons IO.

You can download the full source code of this example here : FileUtilsExample.zip

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