文件流式上传

和传统API不一样的是，传统API中文件在被用户读取前，必须等待被保存在内存或者硬盘中（临时文件），这种方法非常简单，但是另一方面却带来了内存和时间上的额外开销。流式API更佳轻量级，它可以让你牺牲一点便利性以换得理想的性能，文件可以直接从网络输入流中获取。

@RequestMapping("/test3")
    public void test3() throws Exception {
        HttpServletRequest httpServletRequest = getHttpServletRequest();
        HttpServletResponse httpServletResponse = getHttpServletResponse();

        //过程监听器
        ProgressListener progressListener = new ProgressListener() {
            /**
             * @param pBytesRead 已经读取的字节数
             * @param pContentLength 总字节数
             * @param pItems 字段编号
             */
            public void update(long pBytesRead, long pContentLength, int pItems) {
                System.out.println("已读取字节：" + pBytesRead);
                System.out.println("总字节：" + pContentLength);
                System.out.println("字段编号：" + pItems);
            }
        };

        DiskFileItemFactory diskFileItemFactory = new DiskFileItemFactory();

        ServletFileUpload servletFileUpload = new ServletFileUpload(diskFileItemFactory);
        //设置允许上传的单个文件最大尺寸，单位字节
        servletFileUpload.setFileSizeMax(1024 * 1024 * 1024 * 10l);
        //设置整个请求的大小的最大值，单位字节
        servletFileUpload.setSizeMax(1024 * 1024 * 1024 * 100l);
        //设置过程监听器
        servletFileUpload.setProgressListener(progressListener);

        boolean isMultipartContent = servletFileUpload.isMultipartContent(httpServletRequest);
        if (isMultipartContent) {
            //开始上传文件并解析请求，按顺序获取各个表单项
            FileItemIterator fileItemIterator = servletFileUpload.getItemIterator(httpServletRequest);
            while (fileItemIterator.hasNext()) {
                FileItemStream fileItemStream = fileItemIterator.next();
                String name = fileItemStream.getFieldName();
                if (fileItemStream.isFormField()) {
                    try (InputStream inputStream = fileItemStream.openStream()) {
                        System.out.println("表单字段：" + name + "，值："
                                + Streams.asString(inputStream, "utf-8"));
                    }
                } else {
                    System.out.println("原始文件名：" + fileItemStream.getName());
                    System.out.println("MIME类型：" + fileItemStream.getContentType());
                    try (
                            //文件输出流
                            BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(new FileOutputStream("d:/" + fileItemStream.getName()));
                            //文件输入流
                            InputStream inputStream = new BufferedInputStream(fileItemStream.openStream());) {
                        byte[] bytes = new byte[1024 * 8];
                        int n;
                        while (-1 != (n = inputStream.read(bytes))) {
                            bufferedOutputStream.write(bytes, 0, n);
                        }
                    }
                }
            }
        }

        try (PrintWriter printWriter = httpServletResponse.getWriter()) {
            httpServletResponse.setContentType("text/html; charset=utf-8");
            printWriter.println("<script>alert('上传成功');</script>");
        }
    }