Can a servlet determine if the posted data is multipart/form-data?

Question

I have a servlet that is used for many different actions, used in the Front Controller pattern. Does anyone know if it is possible to tell if the data posted back to it is enctype="multipart/form-data"? I can't read the request parameters until I decide this, so I can't dispatch the request to the proper controller.

Any ideas?

score 21 · Answer 1 · edited Jan 18 '18 at 01:16

If you are going to try using the request.getContentType() method presented above, be aware that:

request.getContentType() may return null.
request.getContentType() may not be equal to "multipart/form-data", but may just start with it.

With this in mind, the check you should run is :

if (request.getContentType() != null && request.getContentType().toLowerCase().indexOf("multipart/form-data") > -1 ) {
// Multipart logic here
}

score 17 · Accepted Answer · answered Sep 15 '08 at 20:13

17

Yes, the Content-type header in the user agent's request should include multipart/form-data as described in (at least) the HTML4 spec:

http://www.w3.org/TR/html401/interact/forms.html#h-17.13.4.2

answered Sep 15 '08 at 20:13

Loren Segal

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score 8 · Answer 3 · edited Jan 18 '18 at 00:38

8

You can call a method to get the content type.

http://java.sun.com/j2ee/sdk_1.3/techdocs/api/javax/servlet/ServletRequest.html#getContentType()

According to http://www.w3.org/TR/html401/interact/forms.html#h-17.13.4.2, the content type will be "multipart/form-data".

Don't forget that:

request.getContentType() may return null.
request.getContentType() may not be equal to "multipart/form-data", but may just start with it.

So, with all this in mind:

if (request.getContentType() != null && 
    request.getContentType().toLowerCase().indexOf("multipart/form-data") > -1 ) 
{
    << code block >>
}

edited Jan 18 '18 at 00:38

pradosh nair

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answered Sep 15 '08 at 20:17

Kyle Boon

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3

Kyle, you changed your answer to be my answer after I submitted the *correct* answer. Perhaps at least referencing this fact might be cool... – Darren Hicks Apr 13 '14 at 04:30

score 3 · Answer 4 · answered Aug 10 '11 at 12:54

ServletFileUpload implements isMultipartContent(). Perhaps you can lift this implementation (as opposed to going through the overhead to create a ServletFileUpload) for your needs.

http://www.docjar.com/html/api/org/apache/commons/fileupload/servlet/ServletFileUpload.java.html

score 1 · Answer 5 · answered Jun 05 '19 at 12:40

To expand on awm129's answer - Apache commons' implementation corresponds to this:

if (request != null 
        && request.getContentType() != null 
        && request.getContentType().toLowerCase(Locale.ENGLISH).startsWith("multipart/")) {
    ...
}

You can write it a lot shorter using Apache commons' org.apache.commons.lang3.StringUtils:

if (StringUtils.startsWithIgnoreCase(request.getContentType(), "multipart/")) { 
    ... 
}

score 1 · Answer 6 · answered Sep 15 '08 at 20:19

1

You'll have to read the request parameters in order to determine this, at least on some level. The ServletRequest class has a getContentType method that you'll want to look at.

answered Sep 15 '08 at 20:19

enricopulatzo

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score 0 · Answer 7 · answered Jan 11 '19 at 06:24

0

https://docs.oracle.com/javaee/6/api/javax/servlet/http/HttpServletRequest.html#getParts()

java.util.Collection getParts()

Throws: ServletException - if this request is not of type multipart/form-data

answered Jan 11 '19 at 06:24

SiuFay

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Can a servlet determine if the posted data is multipart/form-data?

7 Answers7