缩略图开源库 Thumbnailator 的使用

我会带着你远行 2022-05-19 08:19 320阅读 0赞

缩略图开源库 Thumbnailator 可根据已有图片，截取指定范围并缩放，还支持添加水印。本文总结了它的用法。  
  
**作者：**王克锋  
**出处：**[https://kefeng.wang/2017/04/09/thumbnailator/][https_kefeng.wang_2017_04_09_thumbnailator]  
**版权：**[自由转载-非商用-非衍生-保持署名][-_-_-]，转载请标明作者和出处。

## 1 概述 ##

功能需求：对于特定的原始图片，要求输出为 480\*360 的图片。算法为：

*  宽高等比缩放至 width=480(当纵向内容多余时) 或 height=360(当横向内容多余时)；
 *  从图片中心点向四周截取 480\*360 大小的图片，四边多余内容丢掉；
 *  最好能在右下角打上水印。

## 2 开源库 thumbnailator(最佳) ##

特色: 不依赖外部库，轻便高效，任何平台适用，支持缩放、旋转、截取，特别还支持【水印】。  
示例: [https://github.com/coobird/thumbnailator/wiki/Examples][https_github.com_coobird_thumbnailator_wiki_Examples]  
源码: [https://github.com/coobird/thumbnailator][https_github.com_coobird_thumbnailator]  
文档: [https://coobird.github.io/thumbnailator/javadoc/0.4.8/][https_coobird.github.io_thumbnailator_javadoc_0.4.8]

### 2.1 Maven 依赖 ###

Maven: [https://mvnrepository.com/artifact/net.coobird/thumbnailator][https_mvnrepository.com_artifact_net.coobird_thumbnailator]

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

### 2.2 代码 ###

public boolean createImage(String input, String output) {
        try {
            BufferedImage image = ImageIO.read(new File(input));
            // BufferedImage image = ImageIO.read(imageFile.getInputStream());
    
            // 确保原图够大
            if (image.getWidth() < DEST_WIDTH || image.getHeight() < DEST_HEIGHT) {
                logger.warn("ImageFile.createImage({}, {}) too small.", image.getWidth(), image.getHeight());
                return false;
            }
    
            // 按比例缩小至目标尺寸
            Thumbnails.Builder<BufferedImage> builder = Thumbnails.of(image);
            builder.crop(Positions.CENTER).size(DEST_WIDTH, DEST_HEIGHT);
    
            // 添加水印
            BufferedImage watermarkImage = ImageIO.read(new File(watermarkfile));
            builder.watermark(Positions.BOTTOM_RIGHT, watermarkImage, 0.3f);
    
            // 保存
            String fileExt = FilenameUtils.getExtension(output);
            builder.outputFormat(fileExt).toFile(output);
            logger.info("ImageFile.createImage(\"{}\") OK.", output);
            return true;
        } catch (IOException e) {
            logger.warn(e.getMessage());
        }
    
        return false;
    }

## 3 开源库 imgscalr ##

特色: 全部基于 Java 2D，不依赖外部库，轻便高效，任何平台适用，支持缩放、旋转、截取，不支持水印。  
源码: [https://github.com/rkalla/imgscalr][https_github.com_rkalla_imgscalr]

### 3.1 Maven 依赖 ###

Maven: [http://mvnrepository.com/artifact/org.imgscalr/imgscalr-lib][http_mvnrepository.com_artifact_org.imgscalr_imgscalr-lib]

<dependency>
        <groupId>org.imgscalr</groupId>
        <artifactId>imgscalr-lib</artifactId>
        <version>4.2</version>
    </dependency>

### 3.2 代码 ###

public boolean createImage(String input, String output) {
        try {
            BufferedImage image = ImageIO.read(new File(input));
            // BufferedImage image = ImageIO.read(imageFile.getInputStream());
    
            // 确保原图够大
            if (image.getWidth() < DEST_WIDTH || image.getHeight() < DEST_HEIGHT) {
                logger.warn("ImageFile.createImage({}, {}) too small.", image.getWidth(), image.getHeight());
                return false;
            }
    
            // 按比例缩小至目标尺寸
            int x = 0, y = 0;
            BufferedImage resized = null;
            double widthRate = (double) image.getWidth() / DEST_WIDTH;
            double heightRate = (double) image.getHeight() / DEST_HEIGHT;
            if (widthRate > heightRate) { // 宽度过剩
                resized = Scalr.resize(image, Scalr.Method.QUALITY, Scalr.Mode.FIT_TO_HEIGHT, DEST_WIDTH, DEST_HEIGHT, Scalr.OP_ANTIALIAS);
                x = (resized.getWidth() - DEST_WIDTH) / 2;
            } else { // 高度过剩
                resized = Scalr.resize(image, Scalr.Method.QUALITY, Scalr.Mode.FIT_TO_WIDTH, DEST_WIDTH, DEST_HEIGHT, Scalr.OP_ANTIALIAS);
                y = (resized.getHeight() - DEST_HEIGHT) / 2;
            }
    
            // 截取中间部分
            BufferedImage thumbnail = Scalr.crop(resized, x, y, DEST_WIDTH, DEST_HEIGHT);
    
            // 保存
            String fileExt = FilenameUtils.getExtension(output);
            ImageIO.write(thumbnail, fileExt, new File(output));
            logger.info("ImageFile.createImage(\"{}\") OK.", output);
            return true;
        } catch (IOException e) {
            logger.warn(e.getMessage());
        }
    
        return false;
    }

[https_kefeng.wang_2017_04_09_thumbnailator]: https://kefeng.wang/2017/04/09/thumbnailator/
[-_-_-]: https://creativecommons.org/licenses/by-nc-nd/3.0/deed.zh
[https_github.com_coobird_thumbnailator_wiki_Examples]: https://github.com/coobird/thumbnailator/wiki/Examples
[https_github.com_coobird_thumbnailator]: https://github.com/coobird/thumbnailator
[https_coobird.github.io_thumbnailator_javadoc_0.4.8]: https://coobird.github.io/thumbnailator/javadoc/0.4.8/
[https_mvnrepository.com_artifact_net.coobird_thumbnailator]: https://mvnrepository.com/artifact/net.coobird/thumbnailator
[https_github.com_rkalla_imgscalr]: https://github.com/rkalla/imgscalr
[http_mvnrepository.com_artifact_org.imgscalr_imgscalr-lib]: http://mvnrepository.com/artifact/org.imgscalr/imgscalr-lib