How to capture file upload Content from dsp page

So i want to generate this kind of message from IData, while this screenshot was made by request from postman

i want to transform this Json request that are transformed to IData when sent to the IS

{
"partnerReferenceNo":"1231231111",
"additionalInfo":{"channel":"MSM","deviceId":"VAMS"}
}

but i try to construct mimeData and addBodyPart the MimeData generated was wrong

"mimeData": {
        "headers": {
            "name": "JsonData"
        },
        "part": {
            "headers": {
                "1231231111": "1231231111",
                "content-transfer-encoding": "7bit",
                "content-type": "text/plain"
            },
            "part": {
                "smime": "false",
                "headers": {
                    "content-transfer-encoding": "7bit"
                },
                "content": "java.io.ByteArrayInputStream@41d5c6ff"
            }
        }

while i want generate message similar to this

POST / HTTP/1.1
Host: localhost:8000
User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:29.0) Gecko/20100101 Firefox/29.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Cookie: __atuvc=34%7C7; permanent=0; _gitlab_session=226ad8a0be43681acf38c2fab9497240; __profilin=p%3Dt; request_method=GET
Connection: keep-alive
Content-Type: multipart/form-data; boundary=---------------------------9051914041544843365972754266
Content-Length: 554

-----------------------------9051914041544843365972754266
Content-Disposition: form-data; name="text"

text default
-----------------------------9051914041544843365972754266
Content-Disposition: form-data; name="file1"; filename="a.txt"
Content-Type: text/plain

Content of a.txt.

-----------------------------9051914041544843365972754266
Content-Disposition: form-data; name="file2"; filename="a.html"
Content-Type: text/html

<!DOCTYPE html><title>Content of a.html.</title>

-----------------------------9051914041544843365972754266--