0Pricing
API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) · Aula

Pré-processamento e Pós-processamento com Filtros

Aplique filtros para executar ações antes que uma requisição chegue ao serviço e depois que o serviço responda.

Pré-processamento e Pós-processamento com Filtros é uma aula grátis de API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) no CoddyKit. Esta é a aula 3 de 4. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway), e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) inclui 4 aulas no total.

Partes desta aula ainda não foram traduzidas e aparecem em inglês.

Intro to Pre/Post Filters

Welcome! In this lesson, we'll explore how Spring Cloud Gateway filters can process requests before they reach a backend service (pre-processing) and after the service responds (post-processing).

This fine-grained control is crucial for handling complex API gateway tasks.

The Filter Chain Revisited

Recall that filters operate in a chain. Each GatewayFilter or GlobalFilter can perform actions:

  • Before calling chain.filter(exchange): This is pre-processing.
  • After chain.filter(exchange) returns a Mono<Void>: This is post-processing.

The reactive nature of Spring Cloud Gateway, using Mono, makes this sequential execution powerful.

Pre-Processing: Before the Service

Pre-processing filters execute before the gateway forwards the request to your actual backend service. Think of them as interceptors for incoming requests.

Common pre-processing tasks include:

  • Authenticating and authorizing requests
  • Adding or modifying request headers
  • Rewriting the URL path or query parameters
  • Implementing rate limiting

Pre-Filter Example: Add Header

Let's look at a simple pre-processing example: adding a custom header to the request before it reaches the service. Spring Cloud Gateway provides built-in filters like AddRequestHeader for this.

This configuration adds an X-Request-Source header with the value gateway to all requests matching the path /api/pre/**.

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

Try running this full Spring Boot application. It sets up a gateway that adds a request header and routes to a simple echo endpoint within the same application. Check the backend's console or response to see the added header!

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

Post-processing filters execute after the backend service has responded but before the gateway sends that response back to the client.

This allows you to inspect or modify the backend's response.

Typical post-processing tasks include:

  • Modifying response headers or body
  • Logging response details (status, latency)
  • Adding metrics for response processing
  • Implementing response caching

Custom Post-Processing Filter

For post-processing, you often need to create custom filters. These filters use the Mono returned by chain.filter(exchange) to add logic that executes upon successful completion.

The .then(Mono.fromRunnable(() -> { ... })) pattern is common for post-processing actions.

Runnable Post-Filter Code

Here's a full Spring Boot application with a custom GlobalFilter that adds a X-Post-Processed header to every response. Notice how the filter logic is chained using .then(Mono.fromRunnable(...)).

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

Understanding when to use pre vs. post processing is key:

  • Pre-filters: Act on the request before it leaves the gateway. Ideal for security, routing logic, request transformation.
  • Post-filters: Act on the response after it returns from the backend. Ideal for response transformation, logging response details, metrics collection.

Choose the right stage to efficiently manage your API traffic.

Filter Timing Challenge

Consider a Spring Cloud Gateway setup. Which of these tasks are typically performed by filters before forwarding a request to a backend service?

Recap: Pre/Post Processing

Great job! You've learned about the powerful concept of pre-processing and post-processing with Spring Cloud Gateway filters.

  • Pre-filters modify requests before they hit the backend.
  • Post-filters modify responses after the backend has replied.
  • The reactive Mono chain enables precise control over filter execution timing.

This understanding is vital for building robust and feature-rich API gateways!

Perguntas Frequentes

A aula “Pré-processamento e Pós-processamento com Filtros” é grátis?

Sim — o texto completo de “Pré-processamento e Pós-processamento com Filtros” é grátis para ler aqui na web. Para praticá-la interativamente (um editor de código integrado e um tutor de IA 24/7) e desbloquear o restante do curso de API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway), atualize para CoddyKit PRO. O curso de API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) inclui 4 aulas no total.

O que vou aprender em “Pré-processamento e Pós-processamento com Filtros”?

Aplique filtros para executar ações antes que uma requisição chegue ao serviço e depois que o serviço responda. Você pratica API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.

Preciso ter experiência prévia para começar API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway)?

Nenhuma experiência prévia é necessária. API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) no CoddyKit é estruturado para alunos iniciantes até avançados, então você pode começar aqui ou desde o início e aprender no seu ritmo. Esta é a aula 3 de 4.

Quanto tempo leva a aula “Pré-processamento e Pós-processamento com Filtros”?

A maioria das aulas CoddyKit leva cerca de 5–10 minutos. Cada uma é compacta e interativa, então você faz progresso constante e retoma exatamente de onde parou entre web e app.

Posso escrever e executar código nesta aula de API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway)?

Sim. Cada aula de API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) inclui um editor de código integrado, então você escreve e executa código real direto no navegador e recebe feedback de IA instantaneamente — nenhuma configuração local necessária.

Todas as aulas deste curso

  1. Filtros Globais e GatewayFilterFactory
  2. Filtros Personalizados de Requisição e Resposta
  3. Pré-processamento e Pós-processamento com Filtros
  4. GatewayFilters integrados que você deve conhecer
← Voltar para API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway)