Global Filters & GatewayFilterFactory
Understand the concept of global filters and how to use built-in GatewayFilterFactories for common transformations.
Global Filters & GatewayFilterFactory is a free API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
What are Gateway Filters?
In Spring Cloud Gateway, filters are like interceptors that allow you to modify incoming HTTP requests or outgoing HTTP responses.
They provide a powerful way to implement cross-cutting concerns for your API traffic, such as security, logging, or data transformation.
Pre- and Post-Filters
Spring Cloud Gateway supports two main types of filter execution:
- Pre-filters: Executed before the request is sent to the downstream service. Great for authentication, logging, or modifying request headers.
- Post-filters: Executed after the response is received from the downstream service but before it's sent back to the client. Useful for modifying responses, caching, or error handling.
Understanding Global Filters
A Global Filter is applied to every single request that passes through the gateway, regardless of the specific route it matches.
This makes them ideal for concerns that affect all your API traffic, like global logging, security checks, or metrics collection across all services.
They implement the GlobalFilter interface.
Building a Custom Global Filter
Let's create a simple global filter that logs the incoming request path. It needs to implement GlobalFilter and Ordered.
Run this Spring Boot app and access http://localhost:8080/test/hello. You'll see the log in the console!
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
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.server.ServerWebExchange;
import reactor.core.publisher.Mono;
@SpringBootApplication
public class GatewayApp {
public static void main(String[] args) {
SpringApplication.run(GatewayApp.class, args);
}
// A simple route for demonstration
@Bean
public RouteLocator customRouteLocator(RouteLocatorBuilder builder) {
return builder.routes()
.route("test_route", r -> r.path("/test/**")
.uri("http://httpbin.org:80")) // Public test service
.build();
}
@Component
static class MyLoggingFilter implements GlobalFilter, Ordered {
@Override
public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
System.out.println("Global Filter: Request Path -> " + exchange.getRequest().getPath());
return chain.filter(exchange); // Continue filter chain
}
@Override
public int getOrder() {
return -1; // Execute very early
}
}
}Understanding Filter Order
When multiple filters (global or route-specific) are present, their execution order matters.
Filters that implement the Ordered interface define their priority using the getOrder() method. Lower values mean higher priority (executed earlier).
- Negative values: Very high priority.
- Positive values: Lower priority.
- Filters without an explicit order often run later.
What is a GatewayFilterFactory?
While GlobalFilters apply everywhere, a GatewayFilterFactory provides reusable, configurable filters that you can apply to specific routes.
Spring Cloud Gateway comes with many built-in factories for common tasks, like adding/removing headers, rewriting paths, or applying rate limits. You configure them per route.
AddRequestHeader Factory in Action
The AddRequestHeader factory adds a static header to the request before it's forwarded to the backend service.
Run this example and navigate to http://localhost:8080/add-header/test. The response from httpbin.org will show 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;
@SpringBootApplication
public class GatewayApp {
public static void main(String[] args) {
SpringApplication.run(GatewayApp.class, args);
}
@Bean
public RouteLocator customRouteLocator(RouteLocatorBuilder builder) {
return builder.routes()
.route("add_header_route", r -> r.path("/add-header/**")
.filters(f -> f.addRequestHeader("X-Gateway-Custom", "CoddyKit"))
.uri("http://httpbin.org:80/headers")) // Shows request headers
.build();
}
}Exploring More Built-in Factories
Spring Cloud Gateway offers many other powerful GatewayFilterFactory implementations:
RemoveRequestHeader: Removes a specified header.RewritePath: Changes the request URI path.Retry: Retries failed requests.RateLimiter: Applies rate limiting to requests.
These factories simplify common gateway tasks without writing custom code.
Global vs. Route-Specific Filters
When should you use a Global Filter versus a GatewayFilterFactory?
- Choose Global Filters for: Cross-cutting concerns affecting all requests (e.g., global security, logging).
- Choose
GatewayFilterFactory(route-specific) for: Logic specific to certain APIs or groups of routes (e.g., API versioning, specific header manipulation, rate limiting on a particular endpoint).
Global Filter Check
Consider a Spring Cloud Gateway application. Which statement is TRUE about Global Filters?
Global Filters & Factories Recap
We've explored Global Filters, which apply to all requests, and learned how to create a custom one. We also introduced GatewayFilterFactory, which offers reusable, configurable filters for specific routes.
Understanding these filter types and when to use them is crucial for building powerful and flexible API Gateways with Spring Cloud Gateway.
Frequently asked questions
Is the “Global Filters & GatewayFilterFactory” lesson free?
Yes — the full text of “Global Filters & GatewayFilterFactory” is free to read here on the web, and the API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) course, upgrade to CoddyKit PRO.
What will I learn in “Global Filters & GatewayFilterFactory”?
Understand the concept of global filters and how to use built-in GatewayFilterFactories for common transformations. You practise API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway)?
No prior experience is required. API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Global Filters & GatewayFilterFactory” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) lesson?
Yes. Every API Gateway & Reverse Proxy (Nginx + Spring Cloud Gateway) lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Global Filters & GatewayFilterFactory
- Custom Request/Response Filters
- Pre/Post Processing with Filters
- Built-in GatewayFilters You Should Know