JAVA-MANI.BLOGSPOT.COM

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

public class DirectorySizeSample
{
public static void main(String[] args)
{
// Using FileUtils.sizeOfDirectory() we can calculate
// the size of a directory including it sub directory
long size = FileUtils.sizeOfDirectory(new File("C:/Windows"));

System.out.println("Size: " + size + " bytes");
}
}