web项目使用多线程上传文件 不使用注解实现

在web项目中使用多线程上传文件可以提高上传的效率，下面是一个使用多线程上传文件的示例：

public class UploadFileServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    private static final String UPLOAD_DIRECTORY = "uploads";
    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

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        // Check that we have a file upload request
        boolean isMultipart = ServletFileUpload.isMultipartContent(request);

        if (!isMultipart) {
            response.getWriter().println("No file uploaded");
            return;
        }

        // Configure upload settings
        DiskFileItemFactory factory = new DiskFileItemFactory();
        factory.setSizeThreshold(MEMORY_THRESHOLD);
        factory.setRepository(new File(System.getProperty("java.io.tmpdir")));

        ServletFileUpload upload = new ServletFileUpload(factory);
        upload.setFileSizeMax(MAX_FILE_SIZE);
        upload.setSizeMax(MAX_REQUEST_SIZE);

        // Set up a listener to monitor progress
        ProgressListener progressListener = new ProgressListener() {

            private long megaBytes = -1;

            public void update(long bytesRead, long contentLength, int items) {
                long mBytes = bytesRead / 1000000;
                if (megaBytes == mBytes) {
                    return;
                }
                megaBytes = mBytes;
                System.out.println("We are currently reading item " + items + ": " + megaBytes + "MB of " + contentLength / 1000000 + "MB");
            }
        };
        upload.setProgressListener(progressListener);

        // Parse the request
        List<FileItem> items;
        try {
            items = upload.parseRequest(request);
        } catch (FileUploadException e) {
            throw new ServletException("Cannot parse multipart request.", e);
        }

        // Create a task for each file item and execute it in a separate thread
        List<UploadTask> tasks = new ArrayList<>();
        for (FileItem item : items) {
            if (!item.isFormField()) {
                String fileName = new File(item.getName()).getName();
                String filePath = getServletContext().getRealPath("") + File.separator + UPLOAD_DIRECTORY + File.separator + fileName;
                UploadTask task = new UploadTask(item, filePath);
                tasks.add(task);
                new Thread(task).start();
            }
        }

        // Wait for all tasks to complete
        for (UploadTask task : tasks) {
            try {
                task.join();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        response.getWriter().println("All files uploaded successfully");
    }

    private static class UploadTask implements Runnable {

        private FileItem item;
        private String filePath;

        public UploadTask(FileItem item, String filePath) {
            this.item = item;
            this.filePath = filePath;
        }

        @Override
        public void run() {
            try {
                item.write(new File(filePath));
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

    }
}

在上面的示例中，我们使用 Apache Commons FileUpload 库来处理文件上传。我们首先检查是否有文件上传请求，然后设置上传的配置。然后，我们为每个文件项创建一个任务并在单独的线程中执行它。最后，我们等待所有任务完成，然后向用户发送响应。