Vor- und Nachverarbeitung mit Filtern

Intro to Pre/Post Filters

The Filter Chain Revisited

Pre-Processing: Before the Service

Pre-Filter Example: Add Header

spring:
  cloud:
    gateway:
      routes:
        - id: pre_header_route
          uri: http://localhost:8080/service/echo
          predicates:
            - Path=/api/pre/**
          filters:
            - AddRequestHeader=X-Request-Source, gateway

Runnable Pre-Filter Code

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.gateway.route.RouteLocator;
import org.springframework.cloud.gateway.route.builder.RouteLocatorBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestHeader;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
@RestController
public class GatewayApp {

  public static void main(String[] args) {
    SpringApplication.run(GatewayApp.class, args);
  }

  // Dummy backend service to echo headers
  @GetMapping("/service/echo")
  public String echoHeaders(@RequestHeader(required = false) java.util.Map<String, String> headers) {
    return "Backend received headers: " + headers.get("x-request-source");
  }

  @Bean
  public RouteLocator customRouteLocator(RouteLocatorBuilder builder) {
    return builder.routes()
      .route("pre_header_route", r -> r.path("/api/pre/**")
        .filters(f -> f.addRequestHeader("X-Request-Source", "gateway"))
        .uri("http://localhost:8080/service/echo")) // Route to its own dummy backend
      .build();
  }
}

Post-Processing: After the Service

Custom Post-Processing Filter

Runnable Post-Filter Code

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.cloud.gateway.route.RouteLocator;
import org.springframework.cloud.gateway.route.builder.RouteLocatorBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.core.Ordered;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.server.ServerWebExchange;
import reactor.core.publisher.Mono;

@SpringBootApplication
@RestController
public class GatewayApp {

  public static void main(String[] args) {
    SpringApplication.run(GatewayApp.class, args);
  }

  // Dummy backend service
  @GetMapping("/service/data")
  public String getData() {
    return "Backend response data!";
  }

  @Bean
  public RouteLocator customRouteLocator(RouteLocatorBuilder builder) {
    return builder.routes()
      .route("post_filter_route", r -> r.path("/api/post/**")
        .uri("http://localhost:8080/service/data")) // Route to itself
      .build();
  }
}

@Component
class CustomPostFilter implements GlobalFilter, Ordered {

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        return chain.filter(exchange).then(Mono.fromRunnable(() -> {
            // This code runs AFTER the downstream service responds
            exchange.getResponse().getHeaders().add("X-Post-Processed", "true");
            System.out.println("Post-processing: Added X-Post-Processed header.");
        }));
    }

    @Override
    public int getOrder() {
        return -1; // Execute relatively late in the filter chain
    }
}

Pre vs. Post: Key Differences

Filter Timing Challenge

Recap: Pre/Post Processing