Document how to register custom predicates and filters for use in Server MVC configuration

[NiiazKhan]

For Spring Cloud Gateway MVC (without webFlux), an equivalent of AbstractGatewayFilterFactory (Gateway Reactive Server) is needed, which allows writing a custom filter and using it by specifying it in the YAML manifest, as shown in this StackOverflow question.

Currently, to use a custom filter, I am forced to write a @bean RouterFunction in Java.

Refer to the filter in Gateway Reactive Server here: Spring Cloud Gateway - Writing Custom GatewayFilter Factories.

[spencergibb]

No abstract class is needed. What is, is the documentation on how to register predicates and filters for use in configuration rather than java dsl.

[spencergibb]

See

spring-cloud-gateway/spring-cloud-gateway-server-mvc/src/main/resources/META-INF/spring.factories

Lines 1 to 6 in 67fc537

	org.springframework.cloud.gateway.server.mvc.filter.FilterSupplier=\
	org.springframework.cloud.gateway.server.mvc.filter.Bucket4jFilterFunctions.FilterSupplier,\
	org.springframework.cloud.gateway.server.mvc.filter.CircuitBreakerFilterFunctions.FilterSupplier,\
	org.springframework.cloud.gateway.server.mvc.filter.RetryFilterFunctions.FilterSupplier,\
	org.springframework.cloud.gateway.server.mvc.filter.TokenRelayFilterFunctions.FilterSupplier,\
	org.springframework.cloud.gateway.server.mvc.filter.FilterFunctions.FilterSupplier

and

spring-cloud-gateway/spring-cloud-gateway-server-mvc/src/main/resources/META-INF/spring.factories

Lines 12 to 14 in 67fc537

	org.springframework.cloud.gateway.server.mvc.predicate.PredicateSupplier=\
	org.springframework.cloud.gateway.server.mvc.predicate.MvcPredicateSupplier,\
	org.springframework.cloud.gateway.server.mvc.predicate.GatewayRequestPredicates.PredicateSupplier

for now

[spencergibb]

Watch #3250 for a programmatic way to register.