Servlet&JSP (三）上传和下载

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1. 上传

Servlet已经为解析multiple的请求做了很好的封装，只需调用HttpServletRequest的getParts方法就能获得请求体的每一个部分

测试代码如下，要注意自定义的servlet上必须加@MultipartConfig注解，否则会抛出Unable to process parts错误

MultipartConfig注解还有一些参数，如限制文件大小等，需要时可参照文档查看配置

@MultipartConfig()public class UploadServlet extends HttpServlet {/** * serialVersionUID */private static final long serialVersionUID = 1L;@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {if (request != null && ServletFileUpload.isMultipartContent(request)) {Collection<Part> parts = request.getParts();for (Part part : parts) {if (!StringUtils.isEmpty(part.getContentType())) {String fileName = getFilename(part);if (!StringUtils.isEmpty(fileName)) {part.write("E:/WorkspaceExport/" + fileName);}}}}}private String getFilename(Part part) {String dispositionHeader = part.getHeader("content-disposition");String[] elements = dispositionHeader.split(";");for (String element : elements) {if (element.trim().startsWith("filename")) {return element.substring(element.indexOf('=') + 1).trim().replace("\"", "");}}return "";}}

<form action="updateFile" enctype="multipart/form-data" method="post"><input type="file" name="file"/><input type="file" name="file"/><input type="submit" value="上传"/></form>

另附SpringMvc的上传配置方法

<bean id="multipartResolver"class="org.springframework.web.multipart.commons.CommonsMultipartResolver"> <!-- setting maximum upload size --><property name="maxUploadSize" value="100000" /></bean>

@RequestMapping("updateFile")public void updateFile(@RequestParam("file") MultipartFile[] files) throws IllegalStateException, IOException {        for(MultipartFile file : files) {file.transferTo(new File("E:/WorkspaceExport/" + file.getOriginalFilename()));}}

当然，也可以自己new一个Resolver进行操作，或者直接@Autowired配置的multipartResolver再调用，此处也记录下来

@RequestMapping("updateFile")public void updateFile(HttpServletRequest request, HttpServletResponse response)throws IllegalStateException, IOException {CommonsMultipartResolver multipartResolver = new CommonsMultipartResolver(request.getSession().getServletContext());if (multipartResolver.isMultipart(request)) {MultipartHttpServletRequest multiRequest = multipartResolver.resolveMultipart(request);Iterator<String> iter = multiRequest.getFileNames();while (iter.hasNext()) {MultipartFile file = multiRequest.getFile(iter.next());file.transferTo(new File("E:/WorkspaceExport/" + file.getOriginalFilename()));  }}}

各个框架的封装，使得功能的实现越简单

2. 下载

下载首先要设定ContentType为下载内容对应的类型，如果不是很清楚MediaType的话，可以简单的设置为application/octet-stream

另外还需要设置Content-Disposition为attachment;fileName=“”

以下是实装例，此处没有使用Servlet而是在Springmvc的Controller方法中进行设置

@RequestMapping("downloadFile")public void downloadFile(HttpServletRequest request,HttpServletResponse response) throws URISyntaxException {response.setCharacterEncoding("utf-8");        response.setContentType("application/octet-stream");        response.setHeader("Content-Disposition", "attachment;fileName=cities.json");                try(OutputStream os = response.getOutputStream()) {        byte[] fileContent = Files.readAllBytes(Paths.get(ResourceUtils.getURL("classpath:test.txt").toURI()));            if (fileContent.length > 0) {                os.write(fileContent);            }        } catch (FileNotFoundException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        }}

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