@RequestPart is always null with Multipart Request, Spring MVC 3.2.4

Question

I am developing a small RESTful service based on Spring 3.2.4 and following this article to write a custom function to send Multipart Requests.

Firstly, in the controller, I wrote the sample function to test

@RequestMapping(value = "/createUser", method = RequestMethod.POST) public @ResponseBody String createUser(@RequestBody User user) { if (user != null) { log.debug("Username: " + user.getUsername()); } return "Successfully created!"; }

The User object contains a user information which is using Jackson JSON to get and parse data. I also used the cURL to send request and the command I tested

curl http://localhost:8080/user/createUser --data-binary @test.txt -X POST -i -H "Content-Type: application/json"

This is the text.txt

{ "id" : "123456", "username" : "YOUR_USERNAME", "password" : "YOUR_PASSWORD", "email" : "YOUR_EMAIL" }

The application returned "Successfully created!" and logged the username. It worked fine.

Secondly, I thought everything would be simple but I was wrong. When I wrote the following function to send Multipart Requests with the User and MultipartFile objects.

@RequestMapping( value = "/createUser", method = RequestMethod.POST, consumes = {"multipart/mixed", "multipart/form-data"}) public @ResponseBody String createUser( @RequestPart("user") @Valid User user, @RequestPart("file") MultipartFile file) { if (user != null) { log.debug("Username: " + user.getUsername()); // The username is null } return "Successfully created!"; }

I continued to use the cURL to test with the command

curl http://localhost:8080/user/createUser --data-binary @test.txt -X POST -i -H "Content-Type: multipart/mixed; boundary=4ebf00fbcf09"

And the text.txt file was changed

--4ebf00fbcf09 Content-Disposition: form-data; name="user" Content-Type: application/json; charset=UTF-8 Content-Transfer-Encoding: 8bit { "id" : "123456", "username" : "YOUR_USERNAME", "password" : "YOUR_PASSWORD", "email" : "YOUR_EMAIL" } --4ebf00fbcf09 Content-Disposition: form-data; name="file"; filename="no_thumb.jpg" Content-Type: image/jpeg Content-Transfer-Encoding: base64 <... File Data ...> --4ebf00fbcf09--

I am facing the problem that the @RequestPart is always NULL. Details:

The application returned "Successfully created!"
The User object was not null but the server logged the "Username: null" and MultipartFile object was too.

How can I fix it?

Please help me to solve this issue.

Have you seen this docs.spring.io/spring/docs/3.2.x/spring-framework-reference/…? — geoand
– geoand, Commented May 5, 2014 at 8:44
Yes, I have. I changed my code that followed this doc but I still got the "Username: null". Do you have any ideas? — Tan Viet
– Tan Viet, Commented May 5, 2014 at 10:32

raksja · Accepted Answer · 2016-06-17 07:15:19Z

Answer is bit late, but could be useful still. This is what worked for me to attach both a payload and a file, with @RequestPart

@RequestMapping(method = RequestMethod.POST) public @ResponseBody String create(@RequestPart Blah blah, @RequestPart(value = "uploadfile", required=false) MultipartFile) {...}

And with curl command below I'm able to verify this as well

curl -i -X POST -H "Content-Type: multipart/mixed" \ -F "blah={\"name\":\"mypayloadname\"};type=application/json" \ -F "[email protected]" http://localhost:8080/url/path

Make sure you escape the payload content and somevalid.zip (second -F is optional, since required is set to false) should be there in the same directory where curl is executed or replace it with valid path to the file.

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