Servlet 上传下载文件

上传文件

1）在表单中使用表单元素 <input type=“file” />，浏览器在解析表单时，会自动生成一个输入框和一个按钮

2）表单需要上传文件时，需指定表单 enctype 的值为 multipart/form-data

3）Commons-fileupload.jar性能优异,用来处理表单文件上传

public class UploadServlet extends HttpServlet{

	 private static final long serialVersionUID = 1L;

	    // 上传文件存储目录
	    private static final String UPLOAD_DIRECTORY = "upload";

	    // 上传配置
	    private static final int MEMORY_THRESHOLD   = 1024 * 1024 * 3;  // 3MB
	    private static final int MAX_FILE_SIZE      = 1024 * 1024 * 40; // 40MB
	    private static final int MAX_REQUEST_SIZE   = 1024 * 1024 * 50; // 50MB

	    /**
	     * 上传数据及保存文件
	     */
	    protected void doPost(HttpServletRequest request,
	        HttpServletResponse response) throws ServletException, IOException {
	        // 检测是否为多媒体上传
	        if (!ServletFileUpload.isMultipartContent(request)) {
	            // 如果不是则停止
	            PrintWriter writer = response.getWriter();
	            writer.println("Error: 表单必须包含 enctype=multipart/form-data");
	            writer.flush();
	            return;
	        }

	        // 配置上传参数
	        DiskFileItemFactory factory = new DiskFileItemFactory();
	        // 设置内存临界值 - 超过后将产生临时文件并存储于临时目录中
	        factory.setSizeThreshold(MEMORY_THRESHOLD);
	        // 设置临时存储目录
	        factory.setRepository(new File("d:\\tempDirectory"));

	        ServletFileUpload upload = new ServletFileUpload(factory);

	        // 设置最大文件上传值
	        upload.setFileSizeMax(MAX_FILE_SIZE);

	        // 设置最大请求值 (包含文件和表单数据)
	        upload.setSizeMax(MAX_REQUEST_SIZE);

	        // 中文处理
	        upload.setHeaderEncoding("UTF-8"); 

	        // 构造临时路径来存储上传的文件
	        // 这个路径相对当前应用的目录
	        String uploadPath = request.getServletContext().getRealPath("./") + File.separator + UPLOAD_DIRECTORY;

	        // 如果目录不存在则创建
	        File uploadDir = new File(uploadPath);
	        if (!uploadDir.exists()) {
	            uploadDir.mkdir();
	        }

	        try {
	            // 解析请求的内容提取文件数据
	            @SuppressWarnings("unchecked")
	            List<FileItem> formItems = upload.parseRequest(request);

	            if (formItems != null && formItems.size() > 0) {
	                // 迭代表单数据
	                for (FileItem item : formItems) {
	                    // 处理不在表单中的字段
	                    if (!item.isFormField()) {
	                        String fileName = new File(item.getName()).getName();
	                        String filePath = uploadPath + File.separator + fileName;
	                        File storeFile = new File(filePath);
	                        // 在控制台输出文件的上传路径
	                        System.out.println(filePath);
	                        // 保存文件到硬盘
	                        item.write(storeFile);
	                        request.setAttribute("message",
	                            "文件上传成功!");
	                    }
	                }
	            }
	        } catch (Exception ex) {
	            request.setAttribute("message",
	                    "错误信息: " + ex.getMessage());
	        }
	        // 跳转到 message.jsp
	        request.getServletContext().getRequestDispatcher("/message.jsp").forward(
	                request, response);
	    }

}

下载文件

1)通知浏览器其所输出的内容的类型是文件，设置Content-Type 的值为：application/x-msdownload

2)在 attachment 后面还可以指定 filename 参数，是服务器建议浏览器将实体内容保存到文件中的文件名称

public class DownloadServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		response.setContentType("application/x-msdownload"); 

		String fileName = "oracle.docx";
		response.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(fileName, "UTF-8"));

		OutputStream out = response.getOutputStream();
		String pptFileName = "D:\\数据库实践.docx";

		InputStream in = new FileInputStream(pptFileName);
		byte [] buffer = new byte[1024];
		int len = 0;
		while((len = in.read(buffer)) != -1){
			out.write(buffer, 0, len);
		}
		in.close();
	}

}

　　

参考文献： 菜鸟教程http://www.runoob.com/servlet/servlet-tutorial.html