之前有个需求：文件上传时，如果是图片，超出指定大小，就自动压缩。为了实现这个功能，借用了 google的Thumbnails 工具，效果还是蛮好的。
全部代码如下：
private void uploadFile(List<MultipartFile> files) throws IOException{Long imgMaxSize = 1024L * 1024L;List<String> imgsType = new ArrayList<>(Arrays.asList("BMP","JPG","PNG"));if(CollectionUtils.isNotEmpty(files)){for(MultipartFile file : files){String fileName = file.getOriginalFilename();Long fileSize = file.getSize();String fileType = file.getContentType().toUpperCase();InputStream inputStream = file.getInputStream();//如果上传的是图片，且超过指定大小，自动压缩输入流if(imgsType.contains(fileType)&&fileSize>imgMaxSize){ByteArrayOutputStream out = new ByteArrayOutputStream();//压缩输入流，scale是压缩比例；quality是质量比例，0-1之间，越接近1,质量越高Thumbnails.of(inputStream).scale(0.7f).outputQuality(0.25d).toOutputStream(out);InputStream imgInputStream = new ByteArrayInputStream(out.toByteArray());inputStream = imgInputStream;}//保存文件到本地服务器String dirPath = "/src/img/";File dir = new File(dirPath);if(!dir.exists()){dir.mkdirs();}File newFile = new File(dirPath+fileName);newFile.createNewFile();FileOutputStream outStream = new FileOutputStream(newFile);int len;byte[] buffer = new byte[1024];while ((len = inputStream.read(buffer)) != -1) {outStream.write(buffer, 0, len);}outStream.close();}}}
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