SystemIconGetter.java

import java.awt.Color;
import java.awt.Graphics;
import java.awt.MediaTracker;
import java.awt.image.BufferedImage;
import java.io.File;

import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.filechooser.FileSystemView;

import sun.awt.shell.ShellFolder;

public class SystemIconGetter {
	public static void main(String[] args)  {
		try{
			if(args.length == 1){
				final File file = new File(args[0]);
		        saveIconImage(file, 16);
			}else if(args.length == 2){
				final int size = "32".equals(args[1]) ? 32: 16;
				final File file = new File(args[0]);
		        saveIconImage(file, size);
			}else{
				System.err.println(Main.class.getName()+" <path to file> [size]");
				System.err.println("  size: 16(default) or 32");
				System.exit(1);
			}
		}catch(Exception ex){
			ex.printStackTrace();
			System.exit(2);
		}
    }

	private static void saveIconImage(File file, int size) throws Exception {
		//OSからファイルのアイコンイメージを取得
		final ImageIcon icon = (size==16) ?
			(ImageIcon)FileSystemView.getFileSystemView().getSystemIcon(file) :
			new ImageIcon(ShellFolder.getShellFolder(file).getIcon(true));
		//イメージのロードが完了するまで待機
		while(icon.getImageLoadStatus() != MediaTracker.COMPLETE){
			System.out.println("Waiting for loading image.: status="+icon.getImageLoadStatus());
			Thread.sleep(100);
		}
		//イメージのサイズを取得
		final int width  = icon.getIconWidth();
		final int height = icon.getIconHeight();
		System.out.println("icon size=("+width+", "+height+")");
		//BufferdImageを生成し、データを書き込む
		final BufferedImage bimage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
		final Graphics g = bimage.getGraphics();
		g.setColor(new Color(255, 255, 255, 255));
		g.fillRect(0, 0, width, height);
		g.drawImage(icon.getImage(), 0, 0, null);
		g.dispose();
		//
		final File outputFile = new File("output.gif");
		final boolean b = ImageIO.write(bimage, "gif", outputFile);
		System.out.println("Write image: path="+outputFile.getAbsolutePath()+", result="+b);
    }
}