I want to ask a question about the multipart/form data. I find the http header of multipart post and the Content-Type: multipart/form-data; boundary=-----...---boundaryNumbe
In your boundary definition, no hyphens are required. When using that boundary to separate two distinct body parts, you must start with two hyphens, followed by your previously-defined boundary string.
This is explained in RFC 1341 (MIME), and you can find additional information there in the Multipart section (as linked).