Spring Using a URI variable for port in WebClient causes an IllegalStateException

Affects: 6.1.2

In Spring Framework 6.1.1, the following little code snippet worked without any problems:

var uriSpec = WebClient.create()
            .get()
            .uri("http://localhost:{port}/first", 8080);

Now this same code causes the following IllegalStateException:

java.lang.IllegalStateException: The port contains a URI variable but has not been expanded yet: {port}

    at org.springframework.web.util.HierarchicalUriComponents.getPort(HierarchicalUriComponents.java:193)
    at org.springframework.web.util.HierarchicalUriComponents.toUriString(HierarchicalUriComponents.java:488)
    at org.springframework.web.util.DefaultUriBuilderFactory$DefaultUriBuilder.toUriString(DefaultUriBuilderFactory.java:416)
    at org.springframework.web.reactive.function.client.DefaultWebClient$DefaultRequestBodyUriSpec.uri(DefaultWebClient.java:230)
    at org.springframework.web.reactive.function.client.DefaultWebClient$DefaultRequestBodyUriSpec.uri(DefaultWebClient.java:199)

This seems related to the changes made in #30027 and the already mentioned #31882.

Is this a bug, or are we no longer allowed to use URI variables inside the base URL?

Comment From: rstoyanchev

Thanks for the report. This is a regression as a result of the changes for #30027. The assumption there was that toUriString in HierarchicalUriComponents is just simple concatenation, but it's not the case for the port, which attempts to parse.