HTML5 FormData returns null in Java Servlet request.getParameter()

Question

My view is HTML 5. I\'m using FormData to make a AJAX 2 POST to a Servlet. Inside the servlet i\'m trying to read request parameters. I can\'t see any parameters. However, G

Answer 1

The HTML5 FormData API sends a multipart/form-data request. It's initially designed to be able to upload files by ajax, with the new version 2 XMLHttpRequest. Uploading files wasn't possible with the previous version.

The request.getParameter() by default recognizes application/x-www-form-urlencoded requests only. But you're sending a multipart/form-data request. You need to annotate your servlet class with @MultipartConfig so that you can get them by request.getParameter().

@WebServlet
@MultipartConfig
public class YourServlet extends HttpServlet {}

Or, when you're still not on Servlet 3.0 yet, use Apache Commons FileUpload. For a more detailed answer on both approaches, see this: How to upload files to server using JSP/Servlet?

If you don't need to upload files at all, use the "standard" XMLHttpRequest approach instead.

var xhr = new XMLHttpRequest();
var data = "firstName=" + encodeURIComponent(firstName)
        + "&lastName=" + encodeURIComponent(lastName);
xhr.open("POST", targetLocation, true);
xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
xhr.send(data);

This way you don't need @MultipartConfig on your servlet anymore.

See also:

• How to use Servlets and Ajax?
• sending a file as multipart through xmlHttpRequest