Thumbnail이미지는 jdk에도 포함될 만큼 많이 또 쉽게 구현하여 사용할수 있다.
그래서...

=========================== TestThumnamil.java ===========================
import java.awt.Graphics;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

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

public class TestThumbnail
{

    public static final int VERTICAL = 0;
    public static final int HORIZONTAL = 1;

    public static final String IMAGE_JPEG = "jpeg";
    public static final String IMAGE_JPG = "jpg";
    public static final String IMAGE_GIF = "gif";
    public static final String IMAGE_PNG = "png";

    private ImageIcon image;
    private ImageIcon thumb;

    public TestThumbnail()
    {
    }
    /*
    public TestThumbnail(Image image)
    {
     this.image = new ImageIcon(image);
    }
*/
/*
    public TestThumbnail(String fileName)
    {
     image = new ImageIcon(fileName);
    }
    */
    public void setImageFile(String fileName)
    {
     image = new ImageIcon(fileName);
    }

    public Image getThumbnail(int size, int dir)
    {
        if (dir == HORIZONTAL)
        {
            thumb = new ImageIcon(
                image.getImage().getScaledInstance(
                    size, -1, Image.SCALE_SMOOTH)
            );
        }
        else
        {
            thumb = new ImageIcon(
                image.getImage().getScaledInstance(
                    -1, size, Image.SCALE_SMOOTH)
            );
        }
        return thumb.getImage();
    }

    public Image getThumbnail(int size, int dir, int scale)
    {
        if (dir == HORIZONTAL)
        {
            thumb = new ImageIcon(
                image.getImage().getScaledInstance(size, -1, scale)
            );
        }
        else
        {
            thumb = new ImageIcon(
                image.getImage().getScaledInstance(-1, size, scale)
            );
        }
        return thumb.getImage();
    }

    public void saveThumbnail(File file, String imageType)
    {
        if (thumb != null)
        {
            BufferedImage bi = new BufferedImage(
                thumb.getIconWidth(),
                thumb.getIconHeight(),
                BufferedImage.TYPE_INT_RGB
            );
            Graphics g = bi.getGraphics();
            g.drawImage(thumb.getImage(), 0, 0, null);
            try
            {
                ImageIO.write(bi, imageType, file);
            }
            catch (IOException ioe)
            {
                System.out.println("Error occured saving thumbnail");
            }
        }
        else
        {
            System.out.println("Thumbnail has not yet been created");
        }
    }

    public void makeThumbnail(String oriFileName) {

     setImageFile(oriFileName);
     File f = new File(oriFileName);

        getThumbnail(100, TestThumbnail.HORIZONTAL);

        System.out.println(oriFileName.substring(0,oriFileName.indexOf(".")));
        String [] fileArr = oriFileName.split(".");
        //String [] fileArr = oriFileName.split(".");

        System.out.println(oriFileName+","+fileArr.length);
        String imageNamePath  = oriFileName.substring(0,oriFileName.indexOf("."));
        String imageExt = oriFileName.substring(oriFileName.indexOf(".")+1, oriFileName.length());

        String IMG_TYPE = "";
        if(imageExt.equalsIgnoreCase("jpg"))
         IMG_TYPE = TestThumbnail.IMAGE_JPG;
        if(imageExt.equalsIgnoreCase("jpeg"))
         IMG_TYPE = TestThumbnail.IMAGE_JPEG;
        if(imageExt.equalsIgnoreCase("gif"))
         IMG_TYPE = TestThumbnail.IMAGE_GIF;

        saveThumbnail(new File(imageNamePath+"_thumb."+imageExt), IMG_TYPE);

    }

    public static void main(String [] args)
    {
     TestThumbnail ct = new TestThumbnail();

     ct.makeThumbnail("d:/james_start2.jpg");
     /*
     ct.setImageFile("d:/james_start2.jpg");
        ct.getThumbnail(100, TestThumbnail.HORIZONTAL);
        ct.saveThumbnail(new File("d:/james_start2_thumb.jpg"), TestThumbnail.IMAGE_JPEG);
        */
    }

}

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