Allow for easier setting of request/url parameters with TestRestClient

[mdeinum]

We have some OpenAPI specs from external parties we need to use and connect to. Those specs specify, for GET requests at least, request parameters to be supplied to do some filtering. Currently there is no, easy, way to add those to the request.

We now need to manually construct the URL with placeholders for the request parameters and supply them as variables within the uri method.

restTestClient.get().uri("http://example.com/?foo={bar}", Map.of("bar", "baz").exchangeSuccesfully();

It would be a nice extension to be able to do something with param/params akin the header/headers functionality.

restTestClient.get().uri("http://example.com/).params(Map.of("bar", "baz")).exchangeSuccesfully();

or

restTestClient.get().uri("http://example.com/).param("bar", "baz").exchangeSuccesfully();

This would make it easier to reuse static variables for URLs (as generated with OpenAPI generator) and to add the parameters to the URL.

[rstoyanchev]

This applies equally to test clients and to RestClient and WebClient. In the current flow, the URI is fully prepared after the uri method, so at that point it's late to add query parameters. There are a couple of ways to do this.

Supplying the variables as an array is shorter:

restClient.get()
        .uri("http://example.com/?foo={bar}", "baz")

Another option is use part static template, and part builder:

restClient.get()
        .uri("http://example.com/", builder -> builder.queryParam("bar", "baz").build())

Note also that the use of a URI template helps with observability to have a single template for potentially many URI's with different variables values.