FormHttpMessageConverter should not have a dependency on the Jakarta Mail API

[jomastel]

When working with multipartCharset the FormHttpMessageConverter uses the MimeUtility.encodeText method.
This forces a dependency for sending email inside a HTTP converter.
In our case, we now need to import org.springframework.boot:spring-boot-starter-mail to fix this dependency.

Could an alternative import be used here to avoid such dependencies in the case of Content-Type multipart?
We found this issue when using a simple REST API.

[poutsma]

The dependency to MimeUtility was introduced in 2014. In 2016, we introduced the Content-Disposition type, with its own MIME encoding logic in encodeFilename.

I will drop the call to MimeUtility.encodeText in favor of the mechanism in Content-Disposition as of 6.0 M4. This means that we will move from using RFC 2047 to RFC 5987 for filename parameters, as we already do in Spring WebFlux' multipart support.