Gateway Handler Filter Functions

The WebMvc.fn API has the concept of a "before" filter function, a java.util.Function<ServerRequest, ServerRequest> that only acts on the request. Many before filter functions are referenced in org.springframework.cloud.gateway.server.mvc.filter.BeforeFilterFunctions as static factory methods. They are adapted to generic org.springframework.web.servlet.function.HandlerFilterFunction<ServerResponse, ServerResponse> in org.springframework.cloud.gateway.server.mvc.filter.FilterFunctions. Either may be used, but the more specific BeforeFilterFunctions is preferred, where possible, as it is more explicit.

The WebMvc.fn API has the concept of a "after" filter function, a java.util.BiFunction<ServerRequest, ServerResponse, ServerResponse> that can modify the response. Many after filter functions are referenced in org.springframework.cloud.gateway.server.mvc.filter.AfterFilterFunctions as static factory methods. They are adapted to generic org.springframework.web.servlet.function.HandlerFilterFunction<ServerResponse, ServerResponse> in org.springframework.cloud.gateway.server.mvc.filter.FilterFunctions. Either may be used, but the more specific AfterFilterFunctions is preferred, where possible, as it is more explicit.

Some filters can not be classified as a simple before or after filter. These filters do work both prior to and after the proxy request has been made. Some of these include filters located in BodyFilterFunctions, Bucket4jFilterFunctions, `CircuitBreakerFilterFunctions, LoadBalancerFilterFunctions, RetryFilterFunctions, and TokenRelayFilterFunctions, all located in the org.springframework.cloud.gateway.server.mvc.filter package.