Consider using ExtendedWebExchangeDataBinder for functional request binding

[ZIRAKrezovic]

Functional requests gained bind() method as part of #25943

However, it is not possible to obtain a path parameter using bind() method.

Given the router example

import lombok.Data;
import lombok.extern.slf4j.Slf4j;

import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;
import org.springframework.web.reactive.function.server.RouterFunction;
import org.springframework.web.reactive.function.server.RouterFunctions;
import org.springframework.web.reactive.function.server.ServerRequest;
import org.springframework.web.reactive.function.server.ServerResponse;

import reactor.core.publisher.Mono;

@Slf4j
@Component
public class MyRouter {
    @Bean
    public RouterFunction<ServerResponse> myRouter() {
        return RouterFunctions.route()
                .GET("/request/{var}", this::handleGet)
                .build();
    }

    private Mono<ServerResponse> handleGet(ServerRequest request) {
        return request.bind(Variables.class).flatMap(variables -> Mono.empty());
    }

    @Data
    static class Variables {
        private String var;
    }
}

It is not possible to obtain the path parameter variable and bind it this way.

However, if I use the ExtendedWebExchangeDataBinder, it works

import static org.springframework.validation.DataBinder.DEFAULT_OBJECT_NAME;

import lombok.Data;
import lombok.extern.slf4j.Slf4j;

import org.springframework.context.annotation.Bean;
import org.springframework.core.ResolvableType;
import org.springframework.stereotype.Component;
import org.springframework.web.reactive.function.server.RouterFunction;
import org.springframework.web.reactive.function.server.RouterFunctions;
import org.springframework.web.reactive.function.server.ServerRequest;
import org.springframework.web.reactive.function.server.ServerResponse;
import org.springframework.web.reactive.result.method.annotation.ExtendedWebExchangeDataBinder;

import reactor.core.publisher.Mono;

@Slf4j
@Component
public class MyRouter {
    @Bean
    public RouterFunction<ServerResponse> myRouter() {
        return RouterFunctions.route()
                .GET("/request/{var}", this::handleGet)
                .build();
    }

    private Mono<ServerResponse> handleGet(ServerRequest request) {
        var binder = new ExtendedWebExchangeDataBinder(null, DEFAULT_OBJECT_NAME);
        binder.setTargetType(ResolvableType.forClass(Variables.class));
        binder.setRequiredFields("var");
        binder.setAllowedFields("var");

        return binder.construct(request.exchange())
                .then(binder.bind(request.exchange()))
                .then(
                        Mono.defer(
                                () -> {
                                    var result = binder.getBindingResult();
                                    var params = (Variables) result.getTarget();

                                    return Mono.empty();
                                }));
    }

    @Data
    static class Variables {
        private String var;
    }
}

Would you consider supporting the mentioned use-case so we can use path parameters for binding without the boilerplate? Thanks in advance.