localhost:8080cannot relate to a relative link , since they must begin with //(in this case, the -path network, usually called a protocol reference), /or with a path segment that does not contain :.
(In the latter case, you can use ./localhost:8080.)
localhost:8080 as part http://localhost:8080
URI http://localhost:8080, localhost:8080 .
localhost , :8080 - .
localhost:8080 URI
localhost:8080 URI:
localhost URI, localhost:8080 URI.