Support Conditional Parameter Expansion

Hi!

We define our Spring MVC APIs with @RequestParam Optional<Type> something.

It looks like Feign doesn’t handle it well and uses “toString()” version so that Spring fails to convert String -> Optional

[dbaltor]

We can support Optional<T> as a return type. but we do not support is as a @Param. I’ll add this to the backlog for us to consider, however; feel free to submit a PR for this if you cannot wait.

Has support to Optional<T> @Param been implemented in Feign?

[kdavisk6]

@yami12376

We are considering adding support for Level 2-4 uri template expression which will address most of what is discussed in this request. Specifically, we will adhere to the RFC rules regarding what to do when the value is undefined, which in our case is an explicit null. Empty Strings are not considered undefined, just empty, which are still included.

For example, using form style expressions http://localhost:8132/test{?name}, the result would be as follows:

name is present
http://localhost:8132/test?name=value

name is present and empty
http://localhost:8132/test?name=

name is not present
http://localhost:8132/test

The only situation this will not handle is the case where a user may want to override this behavior for a single expression. Using the example above where the desired result is the variable on the query string without the = sign, we would need provide a facility to override the expansion logic. We may also consider extending the capability of the Expander concept for this; however for Feign 11, we are going to focus primarily on the template levels.