Servlet&JSP (三）上传和下载

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;

	@Override
	protected 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();
        }
}