java - What is difference between @FormDataParam and @FormParam

Question

What is the difference between @FormDataParam and @FormParam?

I was using multiple @FormDataParam in a method but it was throwing media unsupported type error. But when I used @FormParam, I got the values.

So, I need to know what is the difference between the two of them?

Answer 1

• @FormDataParam is supposed to be used with Multipart type data (i.e. multipart/form-data or MediaType.MULTIPART_FORM_DATA), which in its raw form looks something like

    Content-Type: multipart/form-data; boundary=AaB03x
  
    --AaB03x
    Content-Disposition: form-data; name="submit-name"
  
    Larry
    --AaB03x
    Content-Disposition: form-data; name="files"; filename="file1.txt"
    Content-Type: text/plain
  
    ... contents of file1.txt ...
    --AaB03x--
  

  Multipart is mainly used for sending binary data, like non-text files, or sending arbitrary, meta, or related data along with files.

• @FormParam is for url-encoded request parameters (i.e. application/x-www-form-urlencoded or MediaType.APPLICATION_FORM_URLENCODED), which in raw form looks like

    param1=value1&param2=value2
  

Both of these types are mainly used in client side forms. For example

<form method="POST" action="someUrl">
    <input name="gender" type="text">
    <input name="name" type="text">
</form>

the above would send the request parameters as application/x-www-form-urlencoded. It would get sent in raw form as

gender=male&name=peeskillet

On the server side, we can use a @FormParam for each named parameter in the form

@FormParam("gender") String gender, @FormParam("name") String name

But if we need to send say an image along with the parameters, application/x-form-url-encoded data type is not sufficient, as it only deals with text. So we need to use Multipart

<form method="POST" action="someUrl", enctype="multipart/form-data">
    <input name="gender" type="text">
    <input name="name" type="text">
    <input name="avatar" type="file">
</form>

Here the Multipart type is specified, now the browser will send out the request with something like

Content-Type: multipart/form-data; boundary=AaB03x

--AaB03x
Content-Disposition: form-data; name="gender"

Male
--AaB03x
Content-Disposition: form-data; name="name"

Peskillet
--AaB03x
Content-Disposition: form-data; name="avatar"; filename="image.png"
Content-Type: image/png

... binary content of image file ...
--AaB03x--

On the server, similar with the application/x-www-form-urlencoded example above, for each Multipart parameter (or field to be more precise), we can use @FormDataParam to signify each parameter

@FormDataParam("gender") String gender,
@FormDataParam("name") String name,
@FormDataParam("avatar") InputStream avatar

See Also:

• Forms in HTML Documents