Expand relative URI for RestTemplate if possible

[quaff]

RestTemplate template = new RestTemplate();
template.setUriTemplateHandler(new DefaultUriBuilderFactory("http://localhost:8080"));
template.getForObject("/users/{id}", String.class, 1);
template.getForObject("/users/1", String.class);
// following will works as above after this commit
template.getForObject(URI.create("/users/1"), String.class);

template.exchange(RequestEntity.method(HttpMethod.GET, "/users/{id}", 1).build(), String.class);
template.exchange(RequestEntity.method(HttpMethod.GET, "/users/1").build(), String.class);
// following will works as above after this commit
template.exchange(RequestEntity.method(HttpMethod.GET, URI.create("/users/1")).build(), String.class);

It will make Spring Boot TestRestTemplate much more cleaner, save it from ubiquitous applyRootUriIfNecessary
https://github.com/spring-projects/spring-boot/blob/05a64ecb2ca237d963866665d3a0e7fd1920fee6/spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/web/client/TestRestTemplate.java#L942-L948

[quaff]

RestTemplate is still relevant, could you review this PR? @rstoyanchev

[rstoyanchev]

This will result in double encoding if the URI has encoded characters, e.g. URI.create("/users/1%202") results in http://localhost:8080/users/1%25202.

Generally with the method variants that take URI, we assume the URI has been fully initialized externally and we don't touch it further. That way if the URI template doesn't work for you for some reason, you can always take over.

I'm not sure why you want to pass a URI for a relative URL, or how you prepare it, but you could use the same UriBuilderFactory to that instead of URI.create.