Spring cloud gateway: How to create a filter - spring-boot

Question

I'm new to spring cloud gateway.
I've been watching some of the youtube videos from the SpringDeveloper channel and am working on the following example:
#Bean
public RouteLocator myRoutes(RouteLocatorBuilder builder) {
return builder.routes()
.route(r -> r.path("/get")
.addRequestHeader("X-SpringOne", "Awesome")
.uri("http://httpbin.org:80"))
.build();
}
Prior to looking at spring cloud gateway, i've also looked at Spring Netflix Zuul. I understand that in Netflix Zuul, you can create filters by creating a class that extends ZuulFilter and define it as a pre, post, route, etc.
However I was wondering how one can create a PRE/ POST filter using Spring cloud gateway?
Any help/ advice is much appreciated.
Thanks.

Answer 1

For a pre filter here is AddRequestHeader (code is executed before chain.filter() call):
public class AddRequestHeaderGatewayFilterFactory extends AbstractNameValueGatewayFilterFactory {
#Override
public GatewayFilter apply(NameValueConfig config) {
return (exchange, chain) -> {
ServerHttpRequest request = exchange.getRequest().mutate()
.header(config.getName(), config.getValue())
.build();
return chain.filter(exchange.mutate().request(request).build());
};
}
}
For a 'post' filter, here is SetStatus (code is run in lambda in chain.filter(exchange).then()):
public class SetStatusGatewayFilterFactory extends AbstractGatewayFilterFactory<SetStatusGatewayFilterFactory.Config> {
#Override
public GatewayFilter apply(Config config) {
final HttpStatus status = ServerWebExchangeUtils.parse(config.status);
return (exchange, chain) -> {
return chain.filter(exchange).then(Mono.fromRunnable(() -> {
// check not really needed, since it is guarded in setStatusCode,
// but it's a good example
if (!exchange.getResponse().isCommitted()) {
setResponseStatus(exchange, status);
}
}));
};
}
}

Answer 2

Here is a simple example in Kotlin: the URI http://.../customers is mapped to the URI obtained from the discovery service (lb = load balanced) for the service named customer and appended with "/". Furthermore, the forwarded request is enhanced with an additional header entry. Hope this helps.
#SpringBootApplication
class Application {
#Bean
fun routes(builder: RouteLocatorBuilder) = builder.routes {
route {
path("/customers")
filters {
setPath("/")
addRequestHeader("aKey", "aValue")
}
uri("lb://customer")
}
}
}

Answer 3

I am not sure this is the correct way to do it because I am also trying to achieve this behavior, I am thinking if this is something that needs to be done:
import org.springframework.cloud.gateway.filter.GatewayFilter;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.web.server.ServerWebExchange;
import reactor.core.publisher.Mono;
public class CustomFilter implements GatewayFilter {
#Override
public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
//code for PRE filter
Mono<Void> v = chain.filter(exchange);
//code for POST filter
return v;
}
}
Let me know if that works for you or if you found another solution.