GatewayFilters - Java

GatewayFilters are a key concept in Spring Cloud Gateway that allows developers to modify requests and responses on the fly. This can be useful for a variety of tasks such as authentication, logging, and rate limiting.

Creating a GatewayFilter

To create a GatewayFilter in Java, you can implement the GatewayFilter interface. This interface has a single method, filter(), which takes in a ServerWebExchange object and a GatewayFilterChain and returns a Mono<Void>.

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 MyGatewayFilter implements GatewayFilter {

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        // Filter logic here
        return chain.filter(exchange);
    }
}

In the filter() method, you can access and modify the request and response using the ServerWebExchange object. Once you have finished modifying the request or response, you need to call chain.filter(exchange) to continue the request processing.

Registering a GatewayFilter

To register a GatewayFilter, you can use Spring's GatewayFilterFactory. This factory allows you to specify the filter class and any properties that it needs.

import org.springframework.cloud.gateway.filter.factory.AbstractGatewayFilterFactory;

public class MyGatewayFilterFactory extends AbstractGatewayFilterFactory<MyGatewayFilterFactory.Config> {

    public MyGatewayFilterFactory() {
        super(Config.class);
    }

    @Override
    public GatewayFilter apply(Config config) {
        return new MyGatewayFilter();
    }

    public static class Config {
        // Configuration properties here
    }
}

In the apply() method, you can instantiate your GatewayFilter and pass any configuration properties that it needs. You can then register the MyGatewayFilterFactory with Spring by creating a @Bean method that returns an instance of it.

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class GatewayConfig {

    @Bean
    public MyGatewayFilterFactory myGatewayFilterFactory() {
        return new MyGatewayFilterFactory();
    }

}

Using a GatewayFilter

To use a GatewayFilter, you can specify it in your application.yml configuration file by its name and any configuration properties.

spring:
  cloud:
    gateway:
      routes:
        - id: my_route
          uri: http://example.com
          predicates:
            - Path=/my-path/**
          filters:
            - MyGatewayFilterFactory

In this example, the MyGatewayFilterFactory is added to the filter chain for the my_route route. Any requests matching the Path=/my-path/** predicate will be passed through the MyGatewayFilter.