thumbnailator 等比例压缩图片

		<dependency>
			<groupId>net.coobird</groupId>
			<artifactId>thumbnailator</artifactId>
			<version>0.4.8</version>
		</dependency>

       // 将谋图片等比例压缩，压缩后最大长度不能超过 limit ，保证图片不变形
        String imageUrl = "C:\\Users\\Administrator\\Pictures\\0.jpg";
        BufferedImage bufferedImage = ImageIO.read(new FileInputStream(new File(imageUrl)));
        int height = bufferedImage.getHeight();
        int width = bufferedImage.getWidth();

        double limit = 300.0;//临界值，保证图片的最大长度(或宽或高取最大)不超过此界限
        double rate = getScale(height, width,limit);

        System.out.println("应该缩放的比例值为 .. " + rate);

        System.out.println(height);
        System.out.println(width);
        if (rate != 0) {
            Thumbnails.of(imageUrl).scale(rate).toFile("C:\\Users\\Administrator\\Pictures\\333333.jpg");
        }else {
            //无需缩放
        }

    /**
     * @param height 高
     * @param width  宽
     * @param limit 应当压缩到的最大值
     * @return
     */
    private static double getScale(int height, int width,double limit ) {
        double rate = 0;//应该缩放的比例值

        if (height <= limit && width <= limit) {
            //未超过界限无需压缩
        } else if (height > limit && width > limit) {//均超过界限
            //取两者中最大长度来计算比例
            rate = (height > width) ?  limit/ height : limit/ width;
        }else if (width > limit){//取宽计算
            rate = limit / width;
        } else if (height > limit) {//取高计算
           rate = limit/ height;
        }
        return rate;
    }

jdk 方式压缩

        int doWithHeight = (int) (rate * height);
        int dowithWidth = (int) (rate * width);
        BufferedImage finalImage = new BufferedImage(dowithWidth, doWithHeight, BufferedImage.TYPE_INT_RGB);
        finalImage.getGraphics().drawImage(bufferedImage.getScaledInstance(dowithWidth, doWithHeight, java.awt.Image.SCALE_SMOOTH), 0, 0, null);
        //图片输出路径，以及图片名
        FileOutputStream  fileOutputStream = new FileOutputStream("C:\\Users\\Administrator\\Pictures\\44444.jpg");
        JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(fileOutputStream);
        encoder.encode(finalImage);
        fileOutputStream.close();

    /**
     * 通过指定压缩质量压缩图片，并保存到目标文件
     */
    public static void compressImageWithQuality(BufferedImage image, File outputFile, double compressionQuality) throws IOException {
        Iterator<ImageWriter> writers = ImageIO.getImageWritersByFormatName("jpg");
        ImageWriter writer = writers.next();
        ImageOutputStream ios = ImageIO.createImageOutputStream(outputFile);
        writer.setOutput(ios);

        // 设置压缩质量参数
        ImageWriteParam param = writer.getDefaultWriteParam();
        param.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
        param.setCompressionQuality((float) compressionQuality);

        // 写入文件
        writer.write(null, new IIOImage(image, null, null), param);

        // 关闭资源
        ios.flush();
        ios.close();
        writer.dispose();
    }