Java ImageIO 圖片水印完整工具類：圖片水印、文字水印、旋轉透明度與縮放填充

工具類：ImageUtil

package com.blogs.image;

import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.*;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;

public class ImageUtil {

    /** 圖片水印：支持旋轉、透明度、位置控制 */
    public static void waterMarkImageByIcon(String iconPath, String srcImgPath,
            String targerPath, Integer degree, Integer width, Integer height, float clarity) {
        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);
            Graphics2D g = buffImg.createGraphics();
            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 (degree != null) {
                g.rotate(Math.toRadians(degree),
                        (double) buffImg.getWidth() / 2, (double) buffImg.getHeight() / 2);
            }

            ImageIcon imgIcon = new ImageIcon(iconPath);
            Image img = imgIcon.getImage();
            g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_ATOP, clarity));
            g.drawImage(img, width, height, null);
            g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER));
            g.dispose();

            os = new FileOutputStream(targerPath);
            ImageIO.write(buffImg, "JPG", os);
            System.out.println("添加水印圖片完成!");
        } catch (Exception e) { e.printStackTrace(); }
        finally { closeQuietly(os); }
    }

    /** 文字水印：支持字體、顏色、旋轉、透明度 */
    public static void waterMarkByText(String logoText, String srcImgPath,
            String targerPath, Integer degree, Integer width, Integer height, Float clarity) {
        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);
            Graphics2D g = buffImg.createGraphics();
            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 (degree != null) {
                g.rotate(Math.toRadians(degree),
                        (double) buffImg.getWidth() / 2, (double) buffImg.getHeight() / 2);
            }

            g.setColor(Color.RED);
            g.setFont(new Font("宋體", Font.BOLD, 30));
            g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_ATOP, clarity));
            g.drawString(logoText, width, height);
            g.dispose();

            os = new FileOutputStream(targerPath);
            ImageIO.write(buffImg, "JPG", os);
            System.out.println("添加水印文字完成!");
        } catch (Exception e) { e.printStackTrace(); }
        finally { closeQuietly(os); }
    }

    /** 等比縮放並居中白邊填充 */
    public static void zoomImage(String srcPath, String destPath, int destHeight, int destWidth) {
        try {
            BufferedImage src = ImageIO.read(new File(srcPath));
            int imgWidth = destWidth, imgHeight = destHeight;
            if (src.getHeight() >= src.getWidth()) {
                imgWidth = (int) Math.round((destHeight * 1.0 / src.getHeight()) * src.getWidth());
            } else {
                imgHeight = (int) Math.round((destWidth * 1.0 / src.getWidth()) * src.getHeight());
            }
            BufferedImage dest = new BufferedImage(destWidth, destHeight, BufferedImage.TYPE_INT_RGB);
            Graphics2D g = dest.createGraphics();
            g.setBackground(Color.WHITE);
            g.clearRect(0, 0, destWidth, destHeight);
            g.drawImage(src.getScaledInstance(imgWidth, imgHeight, Image.SCALE_SMOOTH),
                    (destWidth - imgWidth)/2, (destHeight - imgHeight)/2, null);
            g.dispose();
            ImageIO.write(dest, "JPEG", new File(destPath));
        } catch (IOException e) { e.printStackTrace(); }
    }

    private static void closeQuietly(Closeable c) {
        if (c != null) try { c.close(); } catch (IOException ignored) {}
    }
}

參數說明

關鍵技術點總結

• AlphaComposite.SRC_ATOP：只在源圖像非透明區域顯示水印，配合 clarity 控制疊加透明度。
• Graphics2D.rotate：以畫布中心為軸旋轉，旋轉後座標系改變，繪製座標需相應調整。
• Image.SCALE_SMOOTH：雙線性插值縮放，質量優於 SCALE_FAST、SCALE_REPLICATE。
• ImageIO.write：標準 API 輸出，替代內部 JPEGCodec，支持 PNG、JPEG、BMP、WBMP、GIF（讀）。
• zoomImage：目標尺寸固定，源圖等比縮放居中，空白區填充白色，適合生成固定尺寸縮略圖。