使用过滤器进行前置与后置处理
应用过滤器，在请求到达服务之前（前置）以及服务响应之后（后置）执行操作。
使用过滤器进行前置与后置处理 是 CoddyKit 上的免费 API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) 课时。 这是第 3 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) 课程共包含 4 节课。
本课时的部分内容尚未翻译，以英文显示。
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 aMono<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, gatewayRunnable 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
Monochain enables precise control over filter execution timing.
This understanding is vital for building robust and feature-rich API gateways!
常见问题解答
「使用过滤器进行前置与后置处理」课时是免费的吗？
是的 — 「使用过滤器进行前置与后置处理」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) 课程的其余内容，请升级到 CoddyKit PRO。 API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) 课程共包含 4 节课。
「使用过滤器进行前置与后置处理」这节课中我会学到什么？
应用过滤器，在请求到达服务之前（前置）以及服务响应之后（后置）执行操作。 你通过在浏览器中直接运行的动手代码来练习 API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway)，全天候 AI 导师会在你学习这节课的过程中回答你的问题。
学习 API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) 需要有经验吗？
无需任何先前经验。CoddyKit 上的 API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 3 节课，共 4 节。
「使用过滤器进行前置与后置处理」课时需要多长时间？
大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。
我能在这节 API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) 课中编写并运行代码吗？
能。每节 API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。