ตัวกรองส่วนกลางและ GatewayFilterFactory

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.

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.

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.

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!

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.

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.

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!

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.

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).

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.