http: media-type:multipart / for

https://stackoverflow.com/questions/4526273/what-does-enctype-multipart-form-data-mean/28380690#28380690

1. 如果表单包含文件上传，则使用multipart / form-data，否则使用application / x-www-form-urlencoded，如果省略enctype，则默认为默认值。

So after that initial set of headers follows the request body

https://ec.haxx.se/http-multipart.html

--------------------------d74496d66958873e
Content-Disposition: form-data; name="person"

anonymous
--------------------------d74496d66958873e
Content-Disposition: form-data; name="secret"; filename="file.txt"
Content-Type: text/plain

contents of the file
--------------------------d74496d66958873e--

3. 如何读取请求body：

https://stackoverflow.com/questions/9081079/rest-http-post-multipart-with-json

--HereGoes
Content-Disposition: form-data; name="myJsonString"
Content-Type: application/json

{"foo": "bar"}
--HereGoes
Content-Disposition: form-data; name="photo"
Content-Type: image/jpeg
Content-Transfer-Encoding: base64

<...JPEG content in base64...>
--HereGoes--

4. 上传多张图片

https://hellokoding.com/uploading-multiple-files-example-with-spring-boot/

5. 上传多张图片和json

https://www.mkyong.com/spring-boot/spring-boot-file-upload-example-ajax-and-rest/