Servlets

Sending aditional info to server, and getting customised info from it

Sending parameters to the servlet

Gwtupload allows different mechanisms to send info when uploading a file:

1. Adding parameters to the query-string. It is the simplier way

   • Client

   MultiUploader u = new MultiUploader();
   u.setServletPath(u.getServletPath() + "?myinfo=whatever");

   • Server

   String myInfo = request.getParameter("myinfo");

2. Adding widgets to the FormPanel. It works with either single or multiple uploaders, and you can set the order in the formpanel. Note: to use PHP-APC you have to add hidden fields in the first position.

   • Client

   SingleUploader u = new SingleUploader();
   u.add(new Hidden("myinfo", "whatever"), 0);

   • Server

   for (FileItem item : getSessionFileItems(request)) {
     if (item.isFormField() && "myinfo".equals(item.getFieldName())) {
       String myInfo = item.getString();
     }
   }

3. Changing the prefix of the input file name, you can not use spaces though.

   • Client

   SingleUploader u = new SingleUploader();
   u.setFileInputPrefix("Whatever-"); 

   • Server

   for (FileItem item : getSessionFileItems(request)) {
     if (!item.isFormField()) {
       String myInfo = item.getFieldName().split("-")[0];
     }
   }

Getting additional server information

Note: This information is for gwtupload 0.6.3, in older versions you have to deal with getServerResponse.

When a file is uploaded, gwtupload servlet returns a message which is parsed in client side being available as a java object.

The info not only includes important info only available at server side (size, content-type, etc), but a customized message which you can't send if you are extending UploadAction.

The message can be in any format (text, xml, json).

• Server

  	public class MyServlet extends UploadAction {
  	public String executeAction(HttpServletRequest request, List sessionFiles) throws UploadActionException {
  		String ret = "";
  		for (FileItem item : getSessionItems(request)) {
  			if (!item.isFormField()) {
  				// Do anything with the file.
  				// Update the string to return;
  				ret += "server message";
  			}
  		}
  		super.removeSessionFileItems(request);
  		return ret;
  	}
  }

• Client

  	MultiUploader u = new MultiUploader();
      u.addOnFinishUploadHandler(new OnFinishUploaderHandler() {
  	public void onFinish(IUploader uploader) {
  		if (uploader.getStatus() == Status.SUCCESS) {
  			UploadedInfo info = uploader.getServerInfo();
  			System.out.println("File name " + info.name);
  			System.out.println("File content-type " + info.ctype);
  			System.out.println("File size " + info.size);</p>
  	
  			// Here is the string returned in your servlet
  			System.out.println("Server message " + info.message);
  		}
  	}    
  });

Server Configuration (troubleshooting)

A high number of reported errors are related with the server configuration. * Verify that the servlet-class tag matches your servlet class. * Be sure that your customized servlet is in your classpath and extends UploadAction * The url-pattern should be accessible. I hereby recommend that you use wild-cards, just the configuration listed below works out-of-the-box.

If you are using GAE, please be aware that you will have many problems, so read the specific wiki page for it (not written yet).

web.xml: ``` uploadServlet my.package.MyServlet

uploadServlet
*.gupld

maxSize
3145728

slowUploads
200

noDataTimeout
20000
```

Questions

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Thank you.

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©2011 Manuel Carrasco Moñino