Download attachments using java and javascript.

Download attachments using java and javascript.

In web development, you often need to develop the "Download" module. The following is a simple example.

On the server side, use java for development:

@RequestMapping(value = "download.html", method = RequestMethod.GET)    public void download(String resourceid, HttpServletRequest request, HttpServletResponse response) {       response.setContentType("charset=UTF-8");        File file = new File(path);       response.setHeader("Content-Disposition", "attachment; filename=a");       BufferedInputStream bis = null;       BufferedOutputStream bos = null;       OutputStream fos = null;       InputStream fis = null;       try {            fis = new FileInputStream(file.getAbsolutePath());            bis = new BufferedInputStream(fis);            fos = response.getOutputStream();            bos = new BufferedOutputStream(fos);            int bytesRead = 0;            byte[] buffer = new byte[5 * 1024];            while ((bytesRead = bis.read(buffer)) != -1) {                bos.write(buffer, 0, bytesRead);            }            bos.flush();        }catch(E e){        }finally {            try {                bis.close();                bos.close();                fos.close();                fis.close();            } catch (IOException e) {                e.printStackTrace();            }        }    }

When we request this address at the front end, the server first finds out the file, sets the response header, and then outputs it to the browser through the stream.

When the browser finds in the header that the response body is a stream file, it will automatically call the Save As window for the user to save and download.

The key here is the Content-Disposition Header attribute. Content-Disposition is an extension of the MIME protocol, used to indicate how to make the client display the attachment file.

It can be set to two values:

Inline // Open Online

Attachment // download as an attachment

The value we set here is attachment, so it can be recognized as an attachment and downloaded.

The above section describes how to write data to the server and how to request data from the front end.

There are three frontend requests:

1. Form

<form action='download.html' method='post'>    <input type='submit'/></form>

2. iframe

var iframe = "<iframe style='display:none' src='download.html'></iframe>"body.append(iframe);

When an iframe is appended to the body, the download link is automatically requested.

3. open

window.open("download.html");

How to use Java code to upload and download attachments

Int id = (Integer) request. getSession (). getAttribute ("id ");
DiskFileItemFactory factory = new DiskFileItemFactory ();
ServletFileUpload sfu = new ServletFileUpload (factory );
Sfu. setFileSizeMax (1024*1024); // 1 M
List <FileItem> items = sfu. parseRequest (request );
For (int I = 0; I <items. size (); I ++ ){
FileItem item = items. get (I );
If (! Item. isFormField ()){
ServletContext sctx = getServletContext ();
String picurl = sctx. getRealPath ("upload ");
String fileName = item. getName ();
FileName = fileName. substring (fileName
. LastIndexOf ("\") + 1 );
PicDao picDao = new PicDaoImpl ();
System. err. println (id );
PicDao. savePic (id, fileName );
File file = new File (picurl + "/pic _"
+ StringUtils. leftPad (id + "", 5, '0') + "/"
+ FileName );
Item. write (file );
}
}
Response. sendRedirect ("userDetail. do? Id = "+ id );

Which of the following is a good technique for uploading and downloading java files?

The commons-fileupload and commons-io components can be used to upload large files, multi-file uploads, and resumable data transfer.
JS is required to display the progress bar,
Java itself can provide this function with a single thread and multiple threads.
As for services independent from systems, add one more service module.