方式一：使用Image.getScaledInstance

使用jdk的awt包下的Image.getScaledInstance实现图片的缩放。好处是无需引入第三方jar，缺点是会稍微有点模糊。

工具类ImageUtils：

package utils;import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;public class ImageUtils {/*** 通过BufferedImage图片流调整图片大小*/public static BufferedImage resizeImage(BufferedImage originalImage, int targetWidth, int targetHeight) throws IOException {Image resultingImage = originalImage.getScaledInstance(targetWidth, targetHeight, Image.SCALE_AREA_AVERAGING);BufferedImage outputImage = new BufferedImage(targetWidth, targetHeight, BufferedImage.TYPE_INT_RGB);outputImage.getGraphics().drawImage(resultingImage, 0, 0, null);return outputImage;}/*** BufferedImage图片流转byte[]数组*/public static byte[] imageToBytes(BufferedImage bImage) {ByteArrayOutputStream out = new ByteArrayOutputStream();try {ImageIO.write(bImage, "jpg", out);} catch (IOException e) {e.printStackTrace();}return out.toByteArray();}/*** byte[]数组转BufferedImage图片流*/private static BufferedImage bytesToBufferedImage(byte[] ImageByte) {ByteArrayInputStream in = new ByteArrayInputStream(ImageByte);BufferedImage image = null;try {image = ImageIO.read(in);} catch (IOException e) {e.printStackTrace();}return image;}
}

测试：

1.通过 url 获取图片并调整大小后保存：

import utils.ImageUtils;
import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.net.URL;public class Test {public static void main(String[] args) {try {//通过url获取BufferedImage图像缓冲区URL img = new URL("https://img1.360buyimg.com/image/jfs/t1/38591/20/3737/314695/5cc69c01E1838df09/dd6dce681bd23031.jpg");BufferedImage image = ImageIO.read(img);//获取图片的宽、高System.out.println("Width: " + image.getWidth());System.out.println("Height: " + image.getHeight());//调整图片大小为 400X400尺寸BufferedImage newImage = ImageUtils.resizeImage(image,400,400);//将缓冲区图片保存到 F:/test/pic1.jpg (文件不存在会自动创建文件保存，文件存在会覆盖原文件保存)ImageIO.write(newImage, "jpg", new File("F:/test/pic1.jpg"));} catch (IOException e) {e.printStackTrace();}}
}

2、通过读取图片文件调整大小再保存：

import utils.ImageUtils;
import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;public class Test {public static void main(String[] args) {try {//读取原始图片BufferedImage image = ImageIO.read(new FileInputStream("F:/test/pic1.jpg"));System.out.println("Width: " + image.getWidth());System.out.println("Height: " + image.getHeight());//调整图片大小BufferedImage newImage = ImageUtils.resizeImage(image,200,200);//图像缓冲区图片保存为图片文件(文件不存在会自动创建文件保存，文件存在会覆盖原文件保存)ImageIO.write(newImage, "jpg", new File("F:/test/pic2.jpg"));} catch (IOException e) {e.printStackTrace();}}
}

3、MultipartFile类型的图片文件调整大小再保存：

 public JSONObject imageSizeAdjustment(MultipartFile file) {JSONObject result = new JSONObject();try {//从MultipartFile 中获取 byte[]byte[] bytes = file.getBytes();//byte[]转 InputStream InputStream in = new ByteArrayInputStream(bytes);//读取图片输入流为 BufferedImage BufferedImage image = ImageIO.read(in);System.out.println("Width: " + image.getWidth());System.out.println("Height: " + image.getHeight());//调整图片大小BufferedImage newImage = ImageUtils.resizeImage(image, 200, 200);//图像缓冲区图片保存为图片文件(文件不存在会自动创建文件保存，文件存在会覆盖原文件保存)ImageIO.write(newImage, "jpg", new File("F:/test/pic2.jpg"));} catch (IOException e) {e.printStackTrace();}result.put("code", 1);result.put("note", "成功");return result;}

方式二：使用Thumbnailator

Thumbnailator是Java的开源图像大小调整库，它使用渐进式双线性缩放。它支持JPG，BMP，JPEG，WBMP，PNG和GIF。

通过将以下Maven依赖项添加到我们的pom.xml中，将其包括在我们的项目中：

<dependency><groupId>net.coobird</groupId><artifactId>thumbnailator</artifactId><version>0.4.11</version>
</dependency>

工具类ThumbnailsUtils：

import net.coobird.thumbnailator.Thumbnails;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;public class ThumbnailsUtils{private static final Logger logger = LoggerFactory.getLogger(ThumbnailsUtils.class);/*** 通过BufferedImage图片流调整图片大小*/public static BufferedImage resizeImageOne(BufferedImage originalImage, int targetWidth, int targetHeight) throws Exception {ByteArrayOutputStream outputStream = new ByteArrayOutputStream();Thumbnails.of(originalImage).size(targetWidth, targetHeight).outputFormat("JPEG").outputQuality(1).toOutputStream(outputStream);byte[] data = outputStream.toByteArray();ByteArrayInputStream inputStream = new ByteArrayInputStream(data);return ImageIO.read(inputStream);}/*** BufferedImage图片流转byte[]数组*/public static byte[] imageToBytes(BufferedImage bImage) {ByteArrayOutputStream out = new ByteArrayOutputStream();try {ImageIO.write(bImage, "jpg", out);} catch (IOException e) {logger.error("错误信息: ", e);}return out.toByteArray();}/*** byte[]数组转BufferedImage图片流*/private static BufferedImage bytesToBufferedImage(byte[] ImageByte) {ByteArrayInputStream in = new ByteArrayInputStream(ImageByte);BufferedImage image = null;try {image = ImageIO.read(in);} catch (IOException e) {logger.error("错误信息: ", e);}return image;}
}

测试：

和上面测试基本一样只不过 ImageUtils.resizeImage换成 ThumbnailsUtils.resizeImageOne即可。

• 不修改尺寸直接将Url图片下载并转化为File

/***  将Url转换为File* @param url 图片在线链接* @param pathUrl 下载到本地路径* @return* @throws Exception*/
public static File urltoFile(String url,String pathUrl) throws Exception {HttpURLConnection httpUrl = (HttpURLConnection) new URL(url).openConnection();httpUrl.connect();InputStream ins=httpUrl.getInputStream();// 获取文件后缀String prefix = url.substring(url.lastIndexOf("."));String fileUrl = pathUrl + UUIDUtil.get32UUID()+prefix;File file = new File(fileUrl);//System.getProperty("java.io.tmpdir")缓存if (file.exists()) {file.delete();//如果缓存中存在该文件就删除}OutputStream os = new FileOutputStream(file);int bytesRead;int len = 8192;byte[] buffer = new byte[len];while ((bytesRead = ins.read(buffer, 0, len)) != -1) {os.write(buffer, 0, bytesRead);}os.close();ins.close();return file;
}