一、ImgaeHelper类，对图片压缩，返回BufferedImage

package com.ruoyi.common.utils;

import org.junit.jupiter.api.Test;

import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.awt.image.ColorModel;
import java.awt.image.WritableRaster;
import java.io.*;
/**
 * 图片工具类，完成图片的截取
 * 所有方法返回值均未boolean型
 */
public class ImageHelper {

    /**
     * 实现图像的等比缩放
     * @param source
     * @param targetW
     * @param targetH
     * @return
     */
    private static BufferedImage resize(BufferedImage source, int targetW,
                                        int targetH) {
        // targetW，targetH分别表示目标长和宽
        int type = source.getType();
        BufferedImage target = null;
        double sx = (double) targetW / source.getWidth();
        double sy = (double) targetH / source.getHeight();
        // 这里想实现在targetW，targetH范围内实现等比缩放。如果不需要等比缩放
        // 则将下面的if else语句注释即可
        if (sx < sy) {
            sx = sy;
            targetW = (int) (sx * source.getWidth());
        } else {
            sy = sx;
            targetH = (int) (sy * source.getHeight());
        }
        if (type == BufferedImage.TYPE_CUSTOM) { // handmade
            ColorModel cm = source.getColorModel();
            WritableRaster raster = cm.createCompatibleWritableRaster(targetW,
                    targetH);
            boolean alphaPremultiplied = cm.isAlphaPremultiplied();
            target = new BufferedImage(cm, raster, alphaPremultiplied, null);
        } else
            target = new BufferedImage(targetW, targetH, type);
        Graphics2D g = target.createGraphics();
        // smoother than exlax:
        g.setRenderingHint(RenderingHints.KEY_INTERPOLATION,
                RenderingHints.VALUE_INTERPOLATION_BICUBIC);
        g.drawRenderedImage(source, AffineTransform.getScaleInstance(sx, sy));
        g.dispose();
        return target;
    }

    /**
     * 实现图像的等比缩放和缩放后的截取, 处理成功返回true, 否则返回false
     * @param inFilePath 要截取文件的路径
     * @param outFilePath 截取后输出的路径
     * @param width 要截取宽度
     * @param hight 要截取的高度
     * @throws Exception
     */
    public static boolean compress(String inFilePath, String outFilePath,
                                   int width, int hight) {
        boolean ret = false;
        File file = new File(inFilePath);
        File saveFile = new File(outFilePath);
        InputStream in = null;
        try {
            in = new FileInputStream(file);
            ret = compress(in, saveFile, width, hight);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
            ret = false;
        } finally{
            if(null != in){
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

        return ret;
    }

    /**
     * 实现图像的等比缩放和缩放后的截取, 处理成功返回true, 否则返回false
     * @param in 要截取文件流
     * @param outFilePath 截取后输出的路径
     * @param width 要截取宽度
     * @param hight 要截取的高度
     * @throws Exception
     */
    public static boolean compress(InputStream in, File saveFile,
                                   int width, int hight) {
//     boolean ret = false;
        BufferedImage srcImage = null;
        try {
            srcImage = ImageIO.read(in);
        } catch (IOException e) {
            e.printStackTrace();
            return false;
        }

        if (width > 0 || hight > 0) {
            // 原图的大小
            int sw = srcImage.getWidth();
            int sh = srcImage.getHeight();
            // 如果原图像的大小小于要缩放的图像大小，直接将要缩放的图像复制过去
            if (sw > width && sh > hight) {
                srcImage = resize(srcImage, width, hight);
            } else {
                String fileName = saveFile.getName();
                String formatName = fileName.substring(fileName
                        .lastIndexOf('.') + 1);
                try {
                    ImageIO.write(srcImage, formatName, saveFile);
                } catch (IOException e) {
                    e.printStackTrace();
                    return false;
                }
                return true;
            }
        }
        // 缩放后的图像的宽和高
        int w = srcImage.getWidth();
        int h = srcImage.getHeight();
        // 如果缩放后的图像和要求的图像宽度一样，就对缩放的图像的高度进行截取
        if (w == width) {
            // 计算X轴坐标
            int x = 0;
            int y = h / 2 - hight / 2;
            try {
                saveSubImage(srcImage, new Rectangle(x, y, width, hight), saveFile);
            } catch (IOException e) {
                e.printStackTrace();
                return false;
            }
        }
        // 否则如果是缩放后的图像的高度和要求的图像高度一样，就对缩放后的图像的宽度进行截取
        else if (h == hight) {
            // 计算X轴坐标
            int x = w / 2 - width / 2;
            int y = 0;
            try {
                saveSubImage(srcImage, new Rectangle(x, y, width, hight), saveFile);
            } catch (IOException e) {
                e.printStackTrace();
                return false;
            }
        }

        return true;
    }

    /**
     * 实现图像的等比缩放和缩放后的截取, 处理成功返回true, 否则返回false
     * @param in 图片输入流
     * @param proportion 压缩比
     * @throws Exception
     */
    public static BufferedImage compress(InputStream in, int proportion) {
        if(null == in
                ||proportion < 1){// 检查参数有效性
            //LoggerUtil.error(ImageHelper.class, "--invalid parameter, do nothing!");
            return null;
        }

        BufferedImage srcImage = null;
        try {
            srcImage = ImageIO.read(in);
        } catch (IOException e) {
            e.printStackTrace();
            return null;
        }
        // 原图的大小
        int width = srcImage.getWidth() / proportion;
        int hight = srcImage.getHeight() / proportion;

        srcImage = resize(srcImage, width, hight);

//        // 缩放后的图像的宽和高
//        int w = srcImage.getWidth();
//        int h = srcImage.getHeight();
//        // 如果缩放后的图像和要求的图像宽度一样，就对缩放的图像的高度进行截取
//        if (w == width) {
//            // 计算X轴坐标
//            int x = 0;
//            int y = h / 2 - hight / 2;
//            try {
//                saveSubImage(srcImage, new Rectangle(x, y, width, hight), saveFile);
//            } catch (IOException e) {
//                e.printStackTrace();
//                return false;
//            }
//        }
//        // 否则如果是缩放后的图像的高度和要求的图像高度一样，就对缩放后的图像的宽度进行截取
//        else if (h == hight) {
//            // 计算X轴坐标
//            int x = w / 2 - width / 2;
//            int y = 0;
//            try {
//                saveSubImage(srcImage, new Rectangle(x, y, width, hight), saveFile);
//            } catch (IOException e) {
//                e.printStackTrace();
//                return false;
//            }
//        }

        return srcImage;
    }

    /**
     * 实现缩放后的截图
     * @param image 缩放后的图像
     * @param subImageBounds 要截取的子图的范围
     * @param subImageFile 要保存的文件
     * @throws IOException
     */
    private static void saveSubImage(BufferedImage image,
                                     Rectangle subImageBounds, File subImageFile) throws IOException {
        if (subImageBounds.x < 0 || subImageBounds.y < 0
                || subImageBounds.width - subImageBounds.x > image.getWidth()
                || subImageBounds.height - subImageBounds.y > image.getHeight()) {
            //LoggerUtil.error(ImageHelper.class, "Bad subimage bounds");
            return;
        }
        BufferedImage subImage = image.getSubimage(subImageBounds.x,subImageBounds.y, subImageBounds.width, subImageBounds.height);
        String fileName = subImageFile.getName();
        String formatName = fileName.substring(fileName.lastIndexOf('.') + 1);
        ImageIO.write(subImage, formatName, subImageFile);
    }
}

二、springboot控制器

/**
     * 通用上传请求
     */
    @PostMapping("/common/upload")
    public AjaxResult uploadFile(MultipartFile file) throws Exception
    {
        try
        {
            // 上传文件路径
            String filePath = RuoYiConfig.getUploadPath();
            // 上传并返回新文件名称
            String fileName = FileUploadUtils.upload(filePath, file);
//            String url = serverConfig.getUrl() + fileName;
            AjaxResult ajax = AjaxResult.success();
            ajax.put("fileName", fileName);
//            ajax.put("url", url);
            return ajax;
        }
        catch (Exception e)
        {
            return AjaxResult.error(e.getMessage());
        }
    }

三、相关fileUtil

package com.ruoyi.common.utils.file;

import java.awt.image.BufferedImage;
import java.io.*;

import com.ruoyi.common.utils.ImageHelper;
import org.apache.commons.io.FilenameUtils;
import org.springframework.mock.web.MockMultipartFile;
import org.springframework.web.multipart.MultipartFile;
import com.ruoyi.common.constant.Constants;
import com.ruoyi.common.exception.file.FileNameLengthLimitExceededException;
import com.ruoyi.common.exception.file.FileSizeLimitExceededException;
import com.ruoyi.common.exception.file.InvalidExtensionException;
import com.ruoyi.common.utils.DateUtils;
import com.ruoyi.common.utils.StringUtils;
import com.ruoyi.common.utils.security.Md5Utils;
import com.ruoyi.framework.config.RuoYiConfig;

import javax.imageio.ImageIO;
import javax.imageio.stream.ImageOutputStream;

/**
 * 文件上传工具类
 * 
 * @author ruoyi
 */
public class FileUploadUtils
{
    /**
     * 默认大小 50M
     */
    public static final long DEFAULT_MAX_SIZE = 50 * 1024 * 1024;

    /**
     * 默认的文件名最大长度 100
     */
    public static final int DEFAULT_FILE_NAME_LENGTH = 100;

    /**
     * 默认上传的地址
     */
    private static String defaultBaseDir = RuoYiConfig.getProfile();

    private static int counter = 0;

    public static void setDefaultBaseDir(String defaultBaseDir)
    {
        FileUploadUtils.defaultBaseDir = defaultBaseDir;
    }

    public static String getDefaultBaseDir()
    {
        return defaultBaseDir;
    }

    /**
     * 以默认配置进行文件上传
     *
     * @param file 上传的文件
     * @return 文件名称
     * @throws Exception
     */
    public static final String upload(MultipartFile file) throws IOException
    {
        try
        {
            return upload(getDefaultBaseDir(), file, MimeTypeUtils.DEFAULT_ALLOWED_EXTENSION);
        }
        catch (Exception e)
        {
            throw new IOException(e.getMessage(), e);
        }
    }

    /**
     * 根据文件路径上传
     *
     * @param baseDir 相对应用的基目录
     * @param file 上传的文件
     * @return 文件名称
     * @throws IOException
     */
    public static final String upload(String baseDir, MultipartFile file) throws IOException
    {
        try
        {
            return upload(baseDir, file, MimeTypeUtils.DEFAULT_ALLOWED_EXTENSION);
        }
        catch (Exception e)
        {
            throw new IOException(e.getMessage(), e);
        }
    }

    /**
     * 文件上传
     *
     * @param baseDir 相对应用的基目录
     * @param file 上传的文件
     * @param extension 上传文件类型
     * @return 返回上传成功的文件名
     * @throws FileSizeLimitExceededException 如果超出最大大小
     * @throws FileNameLengthLimitExceededException 文件名太长
     * @throws IOException 比如读写文件出错时
     * @throws InvalidExtensionException 文件校验异常
     */
    public static final String upload(String baseDir, MultipartFile file, String[] allowedExtension)
            throws FileSizeLimitExceededException, IOException, FileNameLengthLimitExceededException,
            InvalidExtensionException
    {
        int fileNamelength = file.getOriginalFilename().length();
        if (fileNamelength > FileUploadUtils.DEFAULT_FILE_NAME_LENGTH)
        {
            throw new FileNameLengthLimitExceededException(FileUploadUtils.DEFAULT_FILE_NAME_LENGTH);
        }

        assertAllowed(file, allowedExtension);

        String fileName = extractFilename(file);

        File desc = getAbsoluteFile(baseDir, fileName);

        //图片按照指定精度压缩
        String extension = getExtension(file);
        if("jpg".equals(extension)||"jpeg".equals(extension)||"png".equals(extension)||"bmp".equals(extension)){
            InputStream input = file.getInputStream();
            BufferedImage bImage=ImageHelper.compress(input,2);
            ByteArrayOutputStream bs = new ByteArrayOutputStream();
            ImageOutputStream imOut = ImageIO.createImageOutputStream(bs);
            ImageIO.write(bImage, extension, imOut);
            InputStream inputStream = new ByteArrayInputStream(bs.toByteArray());
            MultipartFile multipartFile = new MockMultipartFile(fileName,inputStream);
            multipartFile.transferTo(desc);
        }else{
            file.transferTo(desc);
        }
//        String pathFileName = getPathFileName(baseDir, fileName);
        return fileName;
    }

    /**
     * 编码文件名
     */
    public static final String extractFilename(MultipartFile file)
    {
        String fileName = file.getOriginalFilename();
        String extension = getExtension(file);
        fileName = DateUtils.datePath() + "/" + encodingFilename(fileName) + "." + extension;
        return fileName;
    }

    private static final File getAbsoluteFile(String uploadDir, String fileName) throws IOException
    {
        File desc = new File(uploadDir + File.separator + fileName);

        if (!desc.getParentFile().exists())
        {
            desc.getParentFile().mkdirs();
        }
        if (!desc.exists())
        {
            desc.createNewFile();
        }
        return desc;
    }

    private static final String getPathFileName(String uploadDir, String fileName) throws IOException
    {
        int dirLastIndex = RuoYiConfig.getProfile().length() + 1;
        String currentDir = StringUtils.substring(uploadDir, dirLastIndex);
        String pathFileName = Constants.RESOURCE_PREFIX + "/" + currentDir + "/" + fileName;
        return pathFileName;
    }

    /**
     * 编码文件名
     */
    private static final String encodingFilename(String fileName)
    {
        fileName = fileName.replace("_", " ");
        fileName = Md5Utils.hash(fileName + System.nanoTime() + counter++);
        return fileName;
    }

    /**
     * 文件大小校验
     *
     * @param file 上传的文件
     * @return
     * @throws FileSizeLimitExceededException 如果超出最大大小
     * @throws InvalidExtensionException
     */
    public static final void assertAllowed(MultipartFile file, String[] allowedExtension)
            throws FileSizeLimitExceededException, InvalidExtensionException
    {
        long size = file.getSize();
        if (DEFAULT_MAX_SIZE != -1 && size > DEFAULT_MAX_SIZE)
        {
            throw new FileSizeLimitExceededException(DEFAULT_MAX_SIZE / 1024 / 1024);
        }

        String fileName = file.getOriginalFilename();
        String extension = getExtension(file);
        if (allowedExtension != null && !isAllowedExtension(extension, allowedExtension))
        {
            if (allowedExtension == MimeTypeUtils.IMAGE_EXTENSION)
            {
                throw new InvalidExtensionException.InvalidImageExtensionException(allowedExtension, extension,
                        fileName);
            }
            else if (allowedExtension == MimeTypeUtils.FLASH_EXTENSION)
            {
                throw new InvalidExtensionException.InvalidFlashExtensionException(allowedExtension, extension,
                        fileName);
            }
            else if (allowedExtension == MimeTypeUtils.MEDIA_EXTENSION)
            {
                throw new InvalidExtensionException.InvalidMediaExtensionException(allowedExtension, extension,
                        fileName);
            }
            else
            {
                throw new InvalidExtensionException(allowedExtension, extension, fileName);
            }
        }

    }

    /**
     * 判断MIME类型是否是允许的MIME类型
     *
     * @param extension
     * @param allowedExtension
     * @return
     */
    public static final boolean isAllowedExtension(String extension, String[] allowedExtension)
    {
        for (String str : allowedExtension)
        {
            if (str.equalsIgnoreCase(extension))
            {
                return true;
            }
        }
        return false;
    }

    /**
     * 获取文件名的后缀
     * 
     * @param file 表单文件
     * @return 后缀名
     */
    public static final String getExtension(MultipartFile file)
    {
        String extension = FilenameUtils.getExtension(file.getOriginalFilename());
        if (StringUtils.isEmpty(extension))
        {
            extension = MimeTypeUtils.getExtension(file.getContentType());
        }
        return extension;
    }
}

四、添加包导入，支持BufferedImage转成inputStream再转成MultipartFile

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
            <version>RELEASE</version>
        </dependency>