Calculate directory size : Directory « File « Java Tutorial

import java.io.File;
import org.apache.commons.io.FileUtils;

public class Main {
  public static void main(String[] args) {
    long size = FileUtils.sizeOfDirectory(new File("C:/Windows"));
    System.out.println("Size: " + size + " bytes");
  }
}

11.4.Directory
	11.4.1.	Create a directory (or several directories)
	11.4.2.	Create directory
	11.4.3.	Create directory along with required nonexistent parent directories
	11.4.4.	Create a directory; all ancestor directories must exist
	11.4.5.	Create a directory; all non-existent ancestor directories are automatically created
	11.4.6.	Create a directories recursively
	11.4.7.	Creates a new and empty directory in the default temp directory using the given prefix.
	11.4.8.	Determine File or Directory
	11.4.9.	Deleting a Directory (an empty directory)
	11.4.10.	Determine if file or directory exists
	11.4.11.	Determine if File or Directory is hidden
	11.4.12.	If a file or directory readable
	11.4.13.	Get name of parent directory
	11.4.14.	Get name of specified file or directory
	11.4.15.	Get parent directory as a File object
	11.4.16.	Get the content of a directory
	11.4.17.	Checks, whether the child directory is a subdirectory of the base directory.
	11.4.18.	Delete file or directory
	11.4.19.	Delete directory recursively
	11.4.20.	Delete file or directory when virtual machine terminates
	11.4.21.	Calculate directory size
	11.4.22.	Change last modified time of a file or directory
	11.4.23.	Mark file or directory Read Only
	11.4.24.	Rename file or directory
	11.4.25.	Moving a File or Directory to Another Directory
	11.4.26.	Search for files recursively
	11.4.27.	Traversing all files and directories under dir
	11.4.28.	Traversing only directories under dir
	11.4.29.	Traversing only files under dir
	11.4.30.	Copying a Directory
	11.4.31.	Check if a directory is not empty
	11.4.32.	Getting the Current Working Directory
	11.4.33.	Get all files and folders under a certain folder and save them to a set
	11.4.34.	Recursively search a directory tree
	11.4.35.	Searches through the directory tree