Java 圖片壓縮與縮放完整實現：等比縮放、質量控制與代碼封裝

核心類：CompressPicDemo

package com.img;

import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import javax.imageio.ImageIO;
import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;

public class CompressPicDemo {
    private File file;
    private String inputDir, outputDir, inputFileName, outputFileName;
    private int outputWidth = 100, outputHeight = 100;
    private boolean proportion = true; // 默認等比縮放

    // 省略 getter/setter ...

    public long getPicSize(String path) {
        file = new File(path);
        return file.length();
    }

    public String compressPic() {
        try {
            file = new File(inputDir + inputFileName);
            if (!file.exists()) return "";
            Image img = ImageIO.read(file);
            if (img.getWidth(null) == -1) return "no";

            int newWidth, newHeight;
            if (proportion) {
                double rate1 = (double) img.getWidth(null) / outputWidth + 0.1;
                double rate2 = (double) img.getHeight(null) / outputHeight + 0.1;
                double rate = Math.max(rate1, rate2);
                newWidth = (int) (img.getWidth(null) / rate);
                newHeight = (int) (img.getHeight(null) / rate);
            } else {
                newWidth = outputWidth;
                newHeight = outputHeight;
            }

            BufferedImage tag = new BufferedImage(newWidth, newHeight, BufferedImage.TYPE_INT_RGB);
            tag.getGraphics().drawImage(
                img.getScaledInstance(newWidth, newHeight, Image.SCALE_SMOOTH), 0, 0, null);

            FileOutputStream out = new FileOutputStream(outputDir + outputFileName);
            JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
            encoder.encode(tag);
            out.close();
            return "ok";
        } catch (IOException ex) {
            ex.printStackTrace();
            return "error";
        }
    }

    // 重載方法支持參數直傳
    public String compressPic(String inputDir, String outputDir, String inputFileName,
                              String outputFileName, int width, int height, boolean gp) {
        this.inputDir = inputDir; this.outputDir = outputDir;
        this.inputFileName = inputFileName; this.outputFileName = outputFileName;
        this.outputWidth = width; this.outputHeight = height; this.proportion = gp;
        return compressPic();
    }

    public static void main(String[] arg) {
        CompressPicDemo demo = new CompressPicDemo();
        System.out.println("原圖大小：" + demo.getPicSize("e:\\1.jpg")/1024 + "KB");
        demo.compressPic("e:\\", "e:\\test\\", "1.jpg", "r1.jpg", 120, 120, false);
    }
}

關鍵技術點

• 等比縮放算法：分別計算寬高縮放比，取較大者作為統一比率，保證圖片完整顯示在目標矩形內。
• Image.SCALE_SMOOTH：優先質量的縮放算法，生成圖片平滑度高，速度稍慢。
• BufferedImage.TYPE_INT_RGB：24位 RGB 模型，適合 JPEG 編碼；若需透明通道用 TYPE_INT_ARGB。
• JPEGImageEncoder：Sun 內部類，生產環境建議替換為 ImageIO.write(tag, "jpg", out) 並配合 ImageWriteParam 控制質量。

補充：圖片縮放帶白邊填充工具方法

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(); }
}