Get Cropped image using Scalr.

FileDownloadThumbnailAction.java

//get file from Mongo Grid file system.
GridFSDBFile file = fileService.getFile(fileId);

//将图片文件转换成一个BufferedImage对象
BufferedImage image = ImageIO.read(file.getInputStream());

//执行对应的操作
BufferedImage thumbnail = Scalr.resize(image, 150);

//获取文件的格式
response.setContentType(file.getContentType());

//写入最终文件到输出流
ImageIO.write(thumbnail, "jpeg", response.getOutputStream());

//刷新输出流，确保文件发送到浏览器
response.flushBuffer();