RestTemplate generator should not require absolute base URL

I have found an issue when working with Spring's RestTemplate generator. I can't create a fully working example at the moment because copy&paste is forbidden outside my customer's virtual development environment.

I have generated RestTemplate clients after Red Hat PAM's JSON swagger file. This allows me to generate a bunch of APIs.
The Swagger file contains a base path that is a relative URL: /services/rest and not the full URL, which is something great

I had created a @Configuration bean that defines the RestTemplate used by ApiClient. It must work multi-environment, as the URL is injected by environment properties.

I have found an issue when setting the base URL

@Configuration
public class PamClientConfiguration{

    @Value(....)
    private String baseUrl;

    @Bean public RestTemplate pamRestTemplate(RestTemplateBuilder restTemplateBuilder){
        return restTemplateBuilder
            .rootUri(baseUrl)
            ......
            // set authentication, logging, etc
            .build();
    }


    @Bean public ApiClient apiClient(RestTemplate pamRestTemplate){
        ApiClient ret = new ApiClient(pamRestTemplate);
        //ret.setBasePath(baseUrl + apiClient.getBasePath())
        return ret;
    }

}

The problem is that I can't use RestTemplate's great feature rootUri with OAG beucase on every API call it will throw an exception that the URI is not a valid URI.

I have identified the possible issue in the following line

https://github.com/OpenAPITools/openapi-generator/blob/cc2dc65496d4d75b5408a08237d96d9221773766/modules/openapi-generator/src/main/resources/Java/libraries/resttemplate/ApiClient.mustache#L690

In my opinion, it should be fromUriString, so that it returns the URI relative string. After that, RestTemplate is likely to add the prefix.

There is a workaround, and in this case is commenting the rootUri of the RestTemplate (with side effects when invoking PAM APIs dynamically), and adding the absolute hostname with ApiClient.setBasePath(baseUrl + apiClient.getBasePath()).

I would like to discuss the opportunity to change that piece of code without creating regressions.

Many thanks

Start at modules/openapi-generator/src/main/resources/Java/libraries/resttemplate/ApiClient.mustache around line 690 and inspect how the generated client parses its base path. Reproduce generation with a relative /services/rest base path and a RestTemplate configured with rootUri; done means the generated client accepts the relative path without invalid-URI errors while preserving absolute-URL behavior.