实现图片上传
用户必须能够上传图片,因此需要文件上传的功能。比较常见的文件上传组件有Commons FileUpload(http://jakarta./commons/fileupload/a>)和COS FileUpload(http://www./cos),Spring已经完全集成了这两种组件,这里我们选择Commons FileUpload。
由于Post一个包含文件上传的Form会以multipart/form-data请求发送给服务器,必须明确告诉DispatcherServlet如何处理MultipartRequest。首先在dispatcher-servlet.xml中声明一个MultipartResolver:
xml 代码
- <bean id="multipartResolver"
- class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
- <!-- 设置上传文件的最大尺寸为1MB -->
- <property name="maxUploadSize">
- <value>1048576</value>
- </property>
- </bean>
这样一旦某个Request是一个MultipartRequest,它就会首先被MultipartResolver处理,然后再转发相应的Controller。
在UploadImageController中,将HttpServletRequest转型为MultipartHttpServletRequest,就能非常方便地得到文件名和文件内容:
java 代码
- public ModelAndView handleRequest(HttpServletRequest request,
- HttpServletResponse response) throws Exception {
- // 转型为MultipartHttpRequest:
- MultipartHttpServletRequest multipartRequest = (MultipartHttpServletRequest) request;
- // 获得文件:
- MultipartFile file = multipartRequest.getFile(" file ");
- // 获得文件名:
- String filename = file.getOriginalFilename();
- // 获得输入流:
- InputStream input = file.getInputStream();
- // 写入文件
-
- // 或者:
- File source = new File(localfileName.toString());
- multipartFile.transferTo(source);
- }
生成缩略图 (目录)
当用户上传了图片后,必须生成缩略图以便用户能快速浏览。我们不需借助第三方软件,JDK标准库就包含了图像处理的API。我们把一张图片按比例缩放到120X120大小,以下是关键代码:
java 代码
- public static void createPreviewImage(String srcFile, String destFile) {
- try {
- File fi = new File(srcFile); // src
- File fo = new File(destFile); // dest
- BufferedImage bis = ImageIO.read(fi);
-
- int w = bis.getWidth();
- int h = bis.getHeight();
- double scale = (double) w / h;
- int nw = IMAGE_SIZE; // final int IMAGE_SIZE = 120;
- int nh = (nw * h) / w;
- if (nh > IMAGE_SIZE) {
- nh = IMAGE_SIZE;
- nw = (nh * w) / h;
- }
- double sx = (double) nw / w;
- double sy = (double) nh / h;
-
- transform.setToScale(sx, sy);
- AffineTransformOp ato = new AffineTransformOp(transform, null);
- BufferedImage bid = new BufferedImage(nw, nh,
- BufferedImage.TYPE_3BYTE_BGR);
- ato.filter(bis, bid);
- ImageIO.write(bid, " jpeg ", fo);
- } catch (Exception e) {
- e.printStackTrace();
- throw new RuntimeException(
- " Failed in create preview image. Error: "
- + e.getMessage());
- }
- }
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