Java实现把图片处理到指定大小的操作方法

<!-- https://mvnrepository.com/artifact/net.coobird/thumbnailator -->
<dependency>
    <groupId>net.coobird</groupId>
    <artifactId>thumbnailator</artifactId>
    <version>0.4.20</version>
</dependency>

@Test
public void test4() {
    String filePath = "/static/dist.jpg"; // 文件路径
    ClassPathResource resource = new ClassPathResource(filePath);
    InputStream inputStream = null;
    try {
        inputStream = resource.getInputStream();
        int i = 0;
        for (float quality = 0.9f; quality > 0.0f; quality -= 0.1f) {
            String path = StrUtil.format("src/main/resources/static/compression_dist_{}.jpg", ++i);
            File distFile = new File(path);
            Thumbnails.of(inputStream)
                    .scale(quality)
                    .outputQuality(1) // 输出的图片质量
                    .toFile(distFile);
            long length = distFile.length();
            if (length / 1024 <= 5120) { // 压缩至5MB左右
                System.out.println(length / (1024 * 1024) + "MB");
                break;
            }
            if (ObjectUtil.isNull(inputStream) || inputStream.available() == 0) {
                inputStream = new FileInputStream(distFile);
            }
            distFile.delete();
        }
    } catch (IOException ex) {
        log.error(ex.getMessage());
        ex.printStackTrace();
    } finally {
        IoUtil.close(inputStream);
    }
}

@Test
public void test() {
    // 1.准备jpg图像编写器
    Iterator<ImageWriter> writers = ImageIO.getImageWritersByFormatName("jpg");
    ImageWriter writer = writers.next();

    ImageWriteParam writeParam = writer.getDefaultWriteParam();
    writeParam.setCompressionMode(ImageWriteParam.MODE_EXPLICIT); // 设置压缩模式

    // 2.准备源文件(要压缩的文件)
    String filePath = "/static/dist.jpg"; // 文件路径
    ClassPathResource resource = new ClassPathResource(filePath);

    // 3.指定目标压缩文件大小（这里按KB计算）
    int targetSize = 5120; // 5MB
    try (InputStream inputStream = resource.getInputStream()) {
        int available = inputStream.available();
        // 4.判断源文件大小是否小于目标压缩大小
        if ((available / 1000) <= targetSize) {
            log.error(StrUtil.format("[{}] 文件小于 {}KB 无需压缩!", resource.getFilename(), targetSize));
            return;
        }
        BufferedImage inputImage = ImageIO.read(inputStream);
        // 设定压缩比例(接近目标文件大小)
        for (float quality = 0.95f; quality > 0.0f; quality -= 0.05f) {
            String path = StrUtil.format("src/main/resources/static/compression_dist_{}.jpg", quality);
            File distFile = new File(path);
            // 输出参数
            ImageOutputStream imageOutputStream = ImageIO.createImageOutputStream(distFile);
            writer.setOutput(imageOutputStream);

            writeParam.setCompressionQuality(quality); // 设置压缩比例(0-1之间)
            writer.write(null, new IIOImage(inputImage, null, null), writeParam);

            // 是否接近于目标大小
            if (distFile.length() / 1024 <= targetSize) {
                IoUtil.close(imageOutputStream);
                break;
            }
            distFile.delete();
        }
    } catch (IOException ex) {
        log.error(ex.getMessage());
        ex.printStackTrace();
    }

    // IoUtil.close(imageOutputStream);
    writer.dispose();
}