转载：java图片压缩工具类(指定压缩大小) - 一个九零後的程序猿 - 博客园 (cnblogs.com)

1:先导入依赖

<!--thumbnailator图片处理-->
        <dependency>
            <groupId>net.coobird</groupId>
            <artifactId>thumbnailator</artifactId>
            <version>0.4.8</version>
        </dependency>

2:创建工具类--->PicUtils

import net.coobird.thumbnailator.Thumbnails;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;

/**
 * @PROJECT_NAME: water_chivalry
 * @AUTHOR: Hanson-Hsc
 * @DATE: 2020-07-27 09:08
 * @DESCRIPTION: 图片压缩工具
 * @VERSION:
 */
public class PicUtils {
　　//以下是常量,按照阿里代码开发规范,不允许代码中出现魔法值
    private static final Logger logger = LoggerFactory.getLogger(PicUtils.class);
    private static final Integer ZERO = 0;
    private static final Integer ONE_ZERO_TWO_FOUR = 1024;
    private static final Integer NINE_ZERO_ZERO = 900;
    private static final Integer THREE_TWO_SEVEN_FIVE = 3275;
    private static final Integer TWO_ZERO_FOUR_SEVEN = 2047;
    private static final Double ZERO_EIGHT_FIVE = 0.85;
    private static final Double ZERO_SIX = 0.6;
    private static final Double ZERO_FOUR_FOUR = 0.44;
    private static final Double ZERO_FOUR = 0.4;

    /**
     * 根据指定大小压缩图片
     *
     * @param imageBytes  源图片字节数组
     * @param desFileSize 指定图片大小，单位kb
     * @return 压缩质量后的图片字节数组
     */
    public static byte[] compressPicForScale(byte[] imageBytes, long desFileSize) {
        if (imageBytes == null || imageBytes.length <= ZERO || imageBytes.length < desFileSize * ONE_ZERO_TWO_FOUR) {
            return imageBytes;
        }
        long srcSize = imageBytes.length;
        double accuracy = getAccuracy(srcSize / ONE_ZERO_TWO_FOUR);
        try {
            while (imageBytes.length > desFileSize * ONE_ZERO_TWO_FOUR) {
                ByteArrayInputStream inputStream = new ByteArrayInputStream(imageBytes);
                ByteArrayOutputStream outputStream = new ByteArrayOutputStream(imageBytes.length);
                Thumbnails.of(inputStream)
                        .scale(accuracy)
                        .outputQuality(accuracy)
                        .toOutputStream(outputStream);
                imageBytes = outputStream.toByteArray();
            }
            logger.info("图片原大小={}kb | 压缩后大小={}kb",
                    srcSize / ONE_ZERO_TWO_FOUR, imageBytes.length / ONE_ZERO_TWO_FOUR);
        } catch (Exception e) {
            logger.error("【图片压缩】msg=图片压缩失败!", e);
        }
        return imageBytes;
    }

    /**
     * 自动调节精度(经验数值)
     *
     * @param size 源图片大小
     * @return 图片压缩质量比
     */
    private static double getAccuracy(long size) {
        double accuracy;
        if (size < NINE_ZERO_ZERO) {
            accuracy = ZERO_EIGHT_FIVE;
        } else if (size < TWO_ZERO_FOUR_SEVEN) {
            accuracy = ZERO_SIX;
        } else if (size < THREE_TWO_SEVEN_FIVE) {
            accuracy = ZERO_FOUR_FOUR;
        } else {
            accuracy = ZERO_FOUR;
        }
        return accuracy;
    }
}

3:在上传图片接口处进行压缩
/**
* 图片上传(招租广告图片专用入口)
*/
@PostMapping("file/img")
@ApiOperation(value = "图片上传接口(广告图片专用入口)")public ResultVo imgUploads(@RequestParam("file") MultipartFile file) throws IOException {
//压缩图片到指定120K以内,不管你的图片有多少兆,都不会超过120kb,精度还算可以,不会模糊
byte[] bytes = PicUtils.compressPicForScale(file.getBytes(), 120);
ByteArrayInputStream inputStream = new ByteArrayInputStream(bytes);
//生成保存在服务器的图片名称，统一修改原后缀名为:jpg
String newFileName = UUID.randomUUID() + ".jpg";
OSSUtil.upload2(newFileName, inputStream);
JSONObject result = new JSONObject();
result.put("url", OSSUtil.getUrl2(newFileName, ""));
return ResultVoUtil.success(result);
}

4.还有一个压缩图片工具类,但是不能指定压缩大小,可是很有用,压缩不会丢失精度,图片也很清晰:

import com.bamboo.water_chivalry.common.enums.ResultEnum;
import com.bamboo.water_chivalry.common.exception.GlobalException;
import org.springframework.web.multipart.MultipartFile;
import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;

/**

• @PROJECT_NAME: water_chivalry

• @AUTHOR: Hanson-Hsc

• @DATE: 2020-07-20 09:24

• @DESCRIPTION: 图片压缩工具

• @VERSION:
  */
  public class ImgCompression {

  public static InputStream getImageCom(MultipartFile file) throws IOException {
  //获取文件输入流
  InputStream inputStream = file.getInputStream();
  try {
  // 把图片读入到内存中
  BufferedImage bufImg = ImageIO.read(inputStream);
  // 压缩代码,存储图片文件byte数组
  ByteArrayOutputStream bos = new ByteArrayOutputStream();
  //防止图片变红,这一步非常重要
  BufferedImage bufferedImage = new BufferedImage(bufImg.getWidth(), bufImg.getHeight(), BufferedImage.TYPE_INT_RGB);
  bufferedImage.createGraphics().drawImage(bufImg,0,0, Color.WHITE,null);
  //先转成jpg格式来压缩,然后在通过OSS来修改成源文件本来的后缀格式
  ImageIO.write(bufferedImage,"jpg",bos);
  //获取输出流
  inputStream = new ByteArrayInputStream(bos.toByteArray());
  return inputStream;
  } catch (IOException e) {
  e.printStackTrace();
  throw new GlobalException(ResultEnum.IMG_UPLOAD_ERROR);
  }finally {
  inputStream.close();
  }
  }
  }