Master Image Processing in Spring Boot 3 with Thumbnailator: From Basics to Advanced

In web development, processing user‑uploaded images is essential; common requirements include resizing, adding watermarks, rotating, and batch generation. This article introduces Thumbnailator , a fluent Java library that simplifies high‑quality thumbnail creation.

1. Maven Dependency

<code><dependency>
  <groupId>net.coobird</groupId>
  <artifactId>thumbnailator</artifactId>
  <version>0.4.20</version>
</dependency></code>

2. Practical Examples

2.1 Create a Thumbnail

<code>Thumbnails.of(new File("d:\\images\\7.png"))
  .size(160, 160)
  .toFile(new File("d:\\images\\output\\7.png"));</code>

Result:

2.2 Add Watermark

<code>Thumbnails.of(new File("d:\\images\\7.png"))
  .size(200, 200)
  .watermark(Positions.BOTTOM_RIGHT, ImageIO.read(new File("d:\\images\\water.png")), 0.5f)
  .outputQuality(0.8)
  .toFile(new File("d:\\images\\output\\7_watermark.png"));</code>

Result:

2.3 Rotate Image

<code>Thumbnails.of(new File("d:\\images\\7.png"))
  .scale(1)
  .rotate(180)
  .toFile(new File("d:\\images\\output\\7_rotate.png"));</code>

Result:

2.4 Force Exact Size

<code>Thumbnails.of(new File("d:\\images\\7.png"))
  .size(200, 200)
  .keepAspectRatio(false)
  .toFile(new File("d:\\images\\output\\7_keepratio.png"));</code>

Result:

2.5 Scale by Factor

<code>Thumbnails.of(new File("d:\\images\\7.png"))
  .scale(0.25)
  .toFile(new File("d:\\images\\output\\7_scale.png"));</code>

Result:

2.6 Batch Generation

<code>File destinationDir = new File("d:\\images\\output");
Thumbnails.of("d:\\images\\1.png", "d:\\images\\2.png", "d:\\images\\3.png")
  .size(200, 200)
  .toFiles(destinationDir, Rename.PREFIX_DOT_THUMBNAIL);</code>

Result:

2.7 Integration with Spring Boot

<code>@PostMapping("/upload")
public void upload(MultipartFile file, HttpServletResponse response) throws Exception {
  InputStream is = file.getInputStream();
  BufferedImage bi = Thumbnails.of(is)
    .size(200, 200)
    .asBufferedImage();
  response.setContentType("image/png");
  response.setHeader("Content-Disposition", "inline; filename=image.png");
  ImageIO.write(bi, "png", response.getOutputStream());
}</code>

Result:

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