從servlet中止上載以限制文件大小

Question

我想限制可以上傳到應用程序的文件的大小。 為了實現這一點，我想在上傳文件的大小超過限制時從服務器端中止上傳過程。

有沒有辦法在不等待HTTP請求完成的情況下從服務器端中止上傳過程？

Answer 1

使用JavaEE 6 / Servlet 3.0，首選方法是在servlet上使用@MultipartConfig注釋 ，如下所示：

@MultipartConfig(location="/tmp", fileSizeThreshold=1024*1024, 
    maxFileSize=1024*1024*5, maxRequestSize=1024*1024*5*5)
public class UploadFileServiceImpl extends HttpServlet ...

Answer 2

你可以這樣做（使用Commons庫）：

    public class UploadFileServiceImpl extends HttpServlet
    {
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException
        {
            response.setContentType("text/plain");

            try
            {
                FileItem uploadItem = getFileItem(request);
                if (uploadItem == null)
                {
                        // ERROR
                }   

                // Add logic here
            }
            catch (Exception ex)
            {
                response.getWriter().write("Error: file upload failure: " + ex.getMessage());           
            }
        }

        private FileItem getFileItem(HttpServletRequest request) throws FileUploadException
        {
            DiskFileItemFactory factory = new DiskFileItemFactory();        

             // Add here your own limit         
             factory.setSizeThreshold(DiskFileItemFactory.DEFAULT_SIZE_THRESHOLD);

         ServletFileUpload upload = new ServletFileUpload(factory);

             // Add here your own limit
             upload.setSizeMax(DiskFileItemFactory.DEFAULT_SIZE_THRESHOLD);


            List<?> items = upload.parseRequest(request);
            Iterator<?> it = items.iterator();
            while (it.hasNext())
            {
                FileItem item = (FileItem) it.next();
                        // Search here for file item
                if (!item.isFormField() && 
                  // Check field name to get to file item  ... 
                {
                    return item;
                }
            }

            return null;
        }
    }

Answer 3

您可以嘗試在servlet的doPost（）方法中執行此操作

multi = new MultipartRequest(request, dirName, FILE_SIZE_LIMIT); 

if(submitButton.equals(multi.getParameter("Submit")))
{
    out.println("Files:");
    Enumeration files = multi.getFileNames();
    while (files.hasMoreElements()) {
    String name = (String)files.nextElement();
    String filename = multi.getFilesystemName(name);
    String type = multi.getContentType(name);
    File f = multi.getFile(name);
    if (f.length() > FILE_SIZE_LIMIT)
    {
        //show error message or
        //return;
        return;
    }
}

這樣您就不必等待完全處理HttpRequest並返回或向客戶端顯示錯誤消息。 HTH

Answer 4

你可以使用apache commons fileupload庫，這個庫也允許你的文件大小。

http://commons.apache.org/fileupload/