ImageUtil 图片缩放与裁剪，不依赖于任何第三方库(以及压缩不变色)

import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import javax.imageio.IIOImage;
import javax.imageio.ImageIO;
import javax.imageio.ImageWriteParam;
import javax.imageio.ImageWriter;
import javax.imageio.metadata.IIOMetadata;
import javax.imageio.stream.ImageOutputStream;
import javax.swing.*;

/**
 * ImageUtil 图片高保真缩放与裁剪，不依赖于任何第三方库
 */
public class ImageUtil {
    public static void main(String[] args) {



//        System.out.println("do....");
//        //BufferedImage bufferedImage = loadImageFile("E:\\test\\jerry.jpg");
//        //save(bufferedImage,"E:\\test\\jerry1.jpg");
//        //缩放图片
//        zoom(100,new File("E:/img/jerry.jpg"),"E:\\img\\jerry100.jpg");
//        //剪切图片
//        BufferedImage crop = crop("E:/img/jerry.jpg", 0, 0, 100, 100);
//        save(crop, "E:\\img\\jerry_crop.jpg");


    }

    private final static String[] imgExts = new String[]{"jpg", "jpeg", "png", "bmp"};

    public static String getExtName(String fileName) {
        int index = fileName.lastIndexOf('.');
        if (index != -1 && (index + 1) < fileName.length()) {
            return fileName.substring(index + 1);
        } else {
            return null;
        }
    }

    /**
     * 通过文件扩展名，判断是否为支持的图像文件，支持则返回 true，否则返回 false
     */
    public static boolean isImageExtName(String fileName) {
        if (fileName == null || fileName.length() ==0) {
            return false;
        }
        fileName = fileName.trim().toLowerCase();
        String ext = getExtName(fileName);
        if (ext != null) {
            for (String s : imgExts) {
                if (s.equals(ext)) {
                    return true;
                }
            }
        }
        return false;
    }

    public static final boolean notImageExtName(String fileName) {
        return !isImageExtName(fileName);
    }

    public static BufferedImage loadImageFile(String sourceImageFileName) {
        if (notImageExtName(sourceImageFileName)) {
            throw new IllegalArgumentException("只支持如下几种类型的图像文件：jpg、jpeg、png、bmp");
        }
        File sourceImageFile = new File(sourceImageFileName);
        if (!sourceImageFile.exists() || !sourceImageFile.isFile()) {
            throw new IllegalArgumentException("文件不存在");
        }
        try {
            return ImageIO.read(sourceImageFile);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * 以 maxWidth 为界对图像进行缩放，高保真保存
     * 1：当图像 width > maxWidth 时，将宽度变为 maxWidth，高度等比例进行缩放，高保真保存
     * 2:当图像 width <= maxWidth 时，宽高保持不变，只进行高保真保存
     */
    public static void zoom(int maxWidth, File srcFile, String saveFile) {
        float quality = 0.8f;
        try {
            //Image 转 BufferedImage 解决变色问题
            Image image = Toolkit.getDefaultToolkit().getImage(srcFile.getPath());
            BufferedImage srcImage = toBufferedImage(image);
            //BufferedImage srcImage = ImageIO.read(srcFile);
            int srcWidth = srcImage.getWidth();
            int srcHeight = srcImage.getHeight();
            // 当宽度在 maxWidth 范围之内，不改变图像宽高，只进行图像高保真保存
            if (srcWidth <= maxWidth) {
                /**
                 * 如果图像不进行缩放的话， resize 就没有必要了，
                 * 经过测试是否有 resize 这一步，生成的结果图像完全一样，一个字节都不差
                 * 所以删掉 resize，可以提升性能，少一步操作
                 */
                // BufferedImage ret = resize(srcImage, srcWidth, srcHeight);
                // saveWithQuality(ret, quality, saveFile);
                saveWithQuality(srcImage, quality, saveFile);
            }
            // 当宽度超出 maxWidth 范围，将宽度变为 maxWidth，而高度按比例变化
            else {
                float scalingRatio = (float) maxWidth / (float) srcWidth;            // 计算缩放比率
                float maxHeight = ((float) srcHeight * scalingRatio);    // 计算缩放后的高度
                BufferedImage ret = resize(srcImage, maxWidth, (int) maxHeight);
                saveWithQuality(ret, quality, saveFile);
            }
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * image转BufferedImage
     * @param image
     * @return
     */
    private static BufferedImage toBufferedImage(Image image) {
        if (image instanceof BufferedImage) {
            return (BufferedImage) image;
        }
        // This code ensures that all the pixels in the image are loaded
        image = new ImageIcon(image).getImage();
        BufferedImage bimage = null;
        GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
        try {
            int transparency = Transparency.OPAQUE;
            GraphicsDevice gs = ge.getDefaultScreenDevice();
            GraphicsConfiguration gc = gs.getDefaultConfiguration();
            bimage = gc.createCompatibleImage(image.getWidth(null), image.getHeight(null), transparency);
        } catch (HeadlessException e) {
            // The system does not have a screen
        }
        if (bimage == null) {
            // Create a buffered image using the default color model
            int type = BufferedImage.TYPE_INT_RGB;
            bimage = new BufferedImage(image.getWidth(null), image.getHeight(null), type);
        }
        // Copy image to buffered image
        Graphics g = bimage.createGraphics();
        // Paint the image onto the buffered image
        g.drawImage(image, 0, 0, null);
        g.dispose();
        return bimage;
    }

    /**
     * 对图片进行剪裁，只保存选中的区域
     * @param sourceImageFile 原图路径
     * @param left            左边从多少开始剪切
     * @param top             右边从多少开始剪切
     * @param width           图片宽度
     * @param height          图片高度
     */
    public static BufferedImage crop(String sourceImageFile, int left, int top, int width, int height) {
        if (notImageExtName(sourceImageFile)) {
            throw new IllegalArgumentException("只支持如下几种类型的图像文件：jpg、jpeg、png、bmp");
        }
        try {
            BufferedImage bi = ImageIO.read(new File(sourceImageFile));
            width = Math.min(width, bi.getWidth());
            height = Math.min(height, bi.getHeight());
            if (width <= 0) {
                width = bi.getWidth();
            }
            if (height <= 0){
                height = bi.getHeight();
            }
            left = Math.min(Math.max(0, left), bi.getWidth() - width);
            top = Math.min(Math.max(0, top), bi.getHeight() - height);
            BufferedImage subImage = bi.getSubimage(left, top, width, height);
            return subImage;    // return ImageIO.write(bi, "jpeg", fileDest);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public static void save(BufferedImage bi, String outputImageFile) {
        FileOutputStream newImage = null;
        try {
            // ImageIO.write(bi, "jpg", new File(outputImageFile));
            ImageIO.write(bi, getExtName(outputImageFile), new File(outputImageFile));
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            if (newImage != null) {
                try {
                    newImage.close();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
        }
    }

    /**
     * 高保真缩放
     */
    public static BufferedImage resize(BufferedImage bi, int toWidth, int toHeight) {
        Graphics g = null;
        try {
            // 从 BufferedImage 对象中获取一个经过缩放的 image
            Image scaledImage = bi.getScaledInstance(toWidth, toHeight, Image.SCALE_SMOOTH);
            // 创建 BufferedImage 对象，存放缩放过的 image
            BufferedImage ret = new BufferedImage(toWidth, toHeight, BufferedImage.TYPE_INT_RGB);
            g = ret.getGraphics();
            g.drawImage(scaledImage, 0, 0, null);
            return ret;
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            if (g != null) {
                g.dispose();
            }
        }
    }

    /**
     * 使用参数为宽：200, 高：200, 质量：0.8，
     * 生成大小为：6.79 KB (6,957 字节)
     * 

     * 如果使用参数为宽：120, 高：120, 质量：0.8，
     * 则生成的图片大小为：3.45 KB (3,536 字节)
     * 

     * 如果使用参数为宽：300, 高：300, 质量：0.5，
     * 则生成的图片大小为：7.54 KB (7,725 字节)
     * 

     * 

     * 建议使用 0.8 的 quality 并且稍大点的宽高
     * 只选用两种质量：0.8 与 0.9，这两个差别不是很大，
     * 但是如果尺寸大些的话，选用 0.8 比 0.9 要划算，因为占用的空间差不多的时候，尺寸大些的更清晰
     */
    public static void saveWithQuality(BufferedImage im, float quality, String outputImageFile) {
        ImageWriter writer = null;
        FileOutputStream newImage = null;
        try {
            // 输出到文件流
            newImage = new FileOutputStream(outputImageFile);

            writer = ImageIO.getImageWritersBySuffix("jpg").next();
            ImageWriteParam param = writer.getDefaultWriteParam();
            param.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
            param.setCompressionQuality(quality);
            ImageOutputStream os = ImageIO.createImageOutputStream(newImage);
            writer.setOutput(os);
            writer.write((IIOMetadata) null, new IIOImage(im, null, null), param);
            os.flush();
            os.close();
        } catch (IOException e) {
            throw new RuntimeException(e);
        } finally {
            if (writer != null) {
                try {
                    writer.dispose();
                } catch (Throwable e) {
                }
            }
            if (newImage != null) {
                try {
                    newImage.close();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
        }
    }
}