Servlet getParameter() returns null for form-data

Question

I am sending a POST request to my localhost Tomcat 8.0 Servlet 3.1 web application but request.getParameter("") returns me null.

This is how I make my request.

I am using PostMan to perform my POST request. And on the java side, I am calling request.getParameter("code") and this gives me null. Same goes for qwe field. I am not using any framework. It's raw servlets. This is only a back-end so it's all about handling the data and responding to client.

If I use "x-www-form-urlencoded", I am able to retrieve the parameters through getParameter() call but I still want to know why I am not able to get form-data.

Thanks.

It's been a while but, I am pretty sure the `form-data` method stores the request content in the body of the request, meaning you'd have to get it using a `Reader` or `InputStream`. — cjstehno, Aug 29 '17 at 19:38
@cjstehno Yes, `getReader()` 's `readLine()` method gives me some data and I am able to see my parameter there but I cannot extract it because it has boundary string and needs to be handled separately (from what I've read). But people say this was handled in Servlet 3.0 and above. I am using 3.1 and I still can't get it. Any suggestions? — OmerHalit, Aug 29 '17 at 19:40
I cannot use `getPart("")` method to get the file from the form data either. — OmerHalit, Aug 29 '17 at 19:52
Yes it would be multipart data and you'd need to use something like the JavaMail multipart library to get it (or the Apache FileUpload API) both of which have multipart implementations that will handle http multipart request content. In your case though, the contained data should just be the bytes of a string of text formatted as a multipart content payload. — cjstehno, Aug 29 '17 at 19:58
@cjstehno What about when I am not sending a file but only string values. Are they still handled as multipart data? How does one access form-data from a servlet? — OmerHalit, Aug 29 '17 at 20:00
You do, but only as multipart body content. The server handles requests of that type differently, "form-data" is really a misnomer in my opinion since its really multipart data, while `x-www-form-urlencoded` is _really_ form data. — cjstehno, Aug 29 '17 at 20:02

score 1 · Accepted Answer · answered Aug 29 '17 at 20:20

Thanks to @cjstehno,

When he said "form-data" was actually a multipart data, then I attempted to read it as multipart data but taking isFormField() method in mind to distinguish between file and parameter. So from a raw servlet, one can read form-data through the code below. From the performance view, I am pretty sure that this might be improved.

try {
     ServletFileUpload upload = new ServletFileUpload();
     FileItemIterator iter = upload.getItemIterator(request);

     while (iter.hasNext()) {
          FileItemStream item = iter.next();
          String name = item.getFieldName();

          if (item.isFormField()) {
               String value = Streams.asString(item.openStream());
          }
     }          
 } catch (Exception ex) {}

For some reason, when I wrap a request, I can't get parameter even though content type was `x-www-form-urlencoded`. I had to change client code to always send form data with content type of `form-data` — Monday Fatigue, Dec 03 '21 at 09:58
Update: I was using custom ServletInputStream implementation and forgot to set isFinished and isReady. — Monday Fatigue, Dec 03 '21 at 11:41

Servlet getParameter() returns null for form-data

1 Answers1