According to RFC 1738 "Uniform Resource Locators (URL)", the scheme names of an URL allows the following characters: lower case letters a to z, digits, the characters plus, period, and hyphen. It also states:
"For resiliency, programs interpreting URLs should treat upper case letters as equivalent to lower case in scheme names (e.g., allow "HTTP" as well as "http")." (section 2.1. The main parts of URLs).
Unfortunately UriComponentsBuilder does not accept the upper case variants HTTP and HTTPS, it throws an IllegalArgumentException instead.