How to add a custom filter specific to a route in Spring Cloud Gateway

Question

So I am new to spring cloud gateway and have just started playing around with it . I was going through the documentation and stumbled upon how to create a custom filter.

https://cloud.spring.io/spring-cloud-gateway/reference/html/#developer-guide

So this is my code for creating a custom filter -

       @Component
      public class CustomPreFilterFactory extends AbstractGatewayFilterFactory<CustomPreFilterFactory.Config> {


      public static class Config {
        //Put the configuration properties for your filter here
      }

     @Override
     public GatewayFilter apply(Config config) {

       return (exchange,chain) ->{
        ServerHttpRequest.Builder builder = exchange.getRequest().mutate();
        System.out.println("Request came in custom pre filter");
        return chain.filter(exchange.mutate().request(builder.build()).build());
      };
    }
  }

Now , I am using java route api provided by gateway for configuring my routes , so this is my route code -

        @Bean
      public RouteLocator myRoutes(RouteLocatorBuilder routeLocatorBuilder) 
{
      return routeLocatorBuilder.routes()
         .route( p -> p.path("/hello").uri("http://localhost:8081"))
        .build();
}

Now , I want to know how to add the custom filter factory which i just created to the route defined above programmatically .

I have looked at the following examples where they register a custom filter factory -

  1. https://www.javainuse.com/spring/cloud-filter
  2. https://medium.com/@niral22/spring-cloud-gateway-tutorial-5311ddd59816

Both of them create routes using properties rather than using the route api .

Any help is much appreciated.

score 1 · Answer 1 · answered Feb 13 '21 at 13:30

This solution worked for me, I created an OrderedGatewayFilter with the injected CustomGatewayFilterFactory like this and added that filter to routes:

@Bean
public RouteLocator myRoutes(RouteLocatorBuilder routeLocatorBuilder, CustomGatewayFilterFactory customGatewayFilterFactory) 
{
    OrderedGatewayFilter orderedGatewayFilter =
      new OrderedGatewayFilter(customGatewayFilterFactory.apply(config), 45);
    return routeLocatorBuilder.routes()
         .route( p -> p.path("/hello").uri("http://localhost:8081").filter(orderedGatewayFilter))
        .build();
}

score 0 · Answer 2 · answered Jul 20 '20 at 09:48

Below is an example of a route that has a predicate defined to match all the request URL with /api/v1/first/** and apply a pre-filter to rewrite the path. There is another filter applied to modify the request header and then route the request to load balanced FIRST-SERVICE.

builder.routes()
            .route(r -> r.path("/api/v1/first/**")
                    .filters(f -> f.rewritePath("/api/v1/first/(?.*)", "/${remains}")
                                    .addRequestHeader("X-first-Header", "first-service-header")
                    )
                    .uri("lb://FIRST-SERVICE/") //downstream endpoint  lb - load balanced
                    .id("queue-service"))

            .build();

Below is the equivalent .yaml configuration.

spring:
  cloud:
    gateway:
      routes:
      - id: first-service
        uri: lb://FIRST-SERVICE
        predicates:
        - Path=/api/v1/first/**
        filters:
        - RewritePath=/api/v1/first/(?.*), /$\{remains}
        - AddRequestHeader=X-first-Header, first-service-header

You can find more such filters in this link.

Hope this is what you are looking for.

The questioner is asking how to add his custom filter "CustomPreFilterFactory". Not existing filters offered by Spring Cloud. — rakesh mehra, Sep 19 '20 at 10:56

score 0 · Answer 3 · answered Sep 19 '20 at 11:15

You need to inject your custom Filter and include it in the route. Something like this..

        @Bean
      public RouteLocator myRoutes(RouteLocatorBuilder routeLocatorBuilder, CustomPreFilterFactory cpf) 
{
      return routeLocatorBuilder.routes()
         .route( p -> p.path("/hello").filters(f -> f.filter(myCustomFilter.apply(new Config()))).uri("http://localhost:8081"))
        .build();
}

How to add a custom filter specific to a route in Spring Cloud Gateway

3 Answers3