code:

package imageShuiying;   

import java.awt.AlphaComposite;
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.RenderingHints;
import java.awt.geom.Line2D;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileOutputStream;
import java.io.OutputStream;
import java.util.Date;
import java.util.Random;

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

/**
 *  给图片打水印
 * @author huoshan
 *
 */
public class ImageMarkLogoByIcon {   

    /**  
     * @param args  
     */  
    public static void main(String[] args) {   
        String srcImgPath = "/home/huoshan/eclipseworkspace/imageShuiying/src/20091026094930-1870243638.jpg";   
        String iconPath = "/home/huoshan/eclipseworkspace/imageShuiying/src/icon.png";   
        String targerPath = "/home/huoshan/eclipseworkspace/imageShuiying/src/"+new Date().toString()+".jpg" ; 
         // 给图片添加水印   
        ImageMarkLogoByIcon.markImageByIcon(iconPath, srcImgPath, targerPath , 0);  
    }   
    /**  
     * 给图片添加水印  
     * @param iconPath 水印图片路径  
     * @param srcImgPath 源图片路径  
     * @param targerPath 目标图片路径  
     */  
    public static void markImageByIcon(String iconPath, String srcImgPath,   
            String targerPath) {   
        markImageByIcon(iconPath, srcImgPath, targerPath, null) ; 
    }   
    /**  
     * 给图片添加水印、可设置水印图片旋转角度  
     * @param iconPath 水印图片路径  
     * @param srcImgPath 源图片路径  
     * @param targerPath 目标图片路径  
     * @param degree 水印图片旋转角度
     */  
    public static void markImageByIcon(String iconPath, String srcImgPath,   
            String targerPath, Integer degree) {   
        OutputStream os = null;   
        try {   
            Image srcImg = ImageIO.read(new File(srcImgPath)); 
            BufferedImage buffImg = new BufferedImage(srcImg.getWidth(null),   
                    srcImg.getHeight(null), BufferedImage.TYPE_INT_RGB); 
            // 得到画笔对象   
            // Graphics g= buffImg.getGraphics();   
            Graphics2D g = buffImg.createGraphics();   

            // 设置对线段的锯齿状边缘处理   
            g.setRenderingHint(RenderingHints.KEY_INTERPOLATION,   
                    RenderingHints.VALUE_INTERPOLATION_BILINEAR);   

            g.drawImage(srcImg.getScaledInstance(srcImg.getWidth(null), srcImg   
                    .getHeight(null), Image.SCALE_SMOOTH), 0, 0, null);   

            if (null != degree) {   
                // 设置水印旋转   
                g.rotate(Math.toRadians(degree),   
                        (double) buffImg.getWidth() / 2, (double) buffImg   
                                .getHeight() / 2);   
            }   
            // 水印图象的路径 水印一般为gif或者png的，这样可设置透明度  
            ImageIcon imgIcon = new ImageIcon(iconPath);   
            // 得到Image对象。   
            Image img = imgIcon.getImage();   
            float alpha = 0.9f; // 透明度   
            g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_ATOP,   
                    alpha));   
            // 表示水印图片的位置   
            g.drawImage(img, 300, 300, null);

            float thick=3.0f;

            g.setStroke(new BasicStroke(thick, BasicStroke.CAP_SQUARE, BasicStroke.JOIN_ROUND));
            g.setColor(Color.black);
            g.drawLine(300, 300, 200, 100);

            g.drawImage(img,200, 100, null);

            g.drawLine(200, 100, 0, 0);

            g.drawImage(img, 0, 0, null);
            g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER));   
            g.dispose();   
            os = new FileOutputStream(targerPath);   
            // 生成图片   
            ImageIO.write(buffImg, "JPG", os);   
        } catch (Exception e) {   
            e.printStackTrace();   
        } finally {   
            try {   
                if (null != os)   
                    os.close();   
            } catch (Exception e) {   
                e.printStackTrace();   
            }   
        }   
    }   
}