问题
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, Google Chrome Dev console shows the request payload. How can I get the same in Servlet code? Any help will be appreciated. Here's the code.
JS code
var xhr = new XMLHttpRequest();
var formData = new FormData();
formData.append('firstName', 'ABC');
formData.append('lastName', 'XYZ');
xhr.open("POST", targetLocation, true);
xhr.send(formData);
Servlet code (both parameters return null)
out.println("Hello! "+ request.getParameter("firstName")+ " "+ request.getParameter("lastName")+ ", thanks for sending your feedback." );
Google Chrome Console
Content-Disposition: form-data; name="firstName"
XYZ
Content-Disposition: form-data; name="lastName"
ABC
回答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
来源：https://stackoverflow.com/questions/10292382/html5-formdata-returns-null-in-java-servlet-request-getparameter