网关 Spring Cloud Gateway 自定义过滤器（全局过滤器以及网关过滤器）

在Spring Cloud Gateway中，创建自定义的过滤器可以通过实现GatewayFilterFactory接口来完成。以下是一个简单的自定义全局过滤器的例子，它会为所有通过网关的请求添加一个自定义响应头：

import org.springframework.cloud.gateway.filter.GatewayFilter;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.filter.factory.GatewayFilterFactory;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DataBufferFactory;
import org.springframework.core.io.buffer.DataBufferUtils;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.web.server.ServerWebExchange;
import reactor.core.publisher.Mono;
 
import java.nio.charset.StandardCharsets;
 
public class CustomGatewayFilterFactory implements GatewayFilterFactory {
 
    @Override
    public GatewayFilter apply(Object config) {
        return (exchange, chain) -> {
            ServerHttpResponse response = exchange.getResponse();
            DataBufferFactory bufferFactory = response.bufferFactory();
            response.getHeaders().set("Custom-Header", "MyValue");
            return chain.filter(exchange).then(Mono.fromRunnable(() -> {
                // 对于所有的响应，这里可以添加额外的逻辑，例如修改响应体等
            }));
        };
    }
}

要注册这个自定义过滤器，你需要在Spring Cloud Gateway应用的配置类中添加@Bean定义：

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.cloud.gateway.filter.factory.GatewayFilterFactory;
 
@Configuration
public class GatewayConfig {
 
    @Bean
    public GatewayFilterFactory customGatewayFilterFactory() {
        return new CustomGatewayFilterFactory();
    }
}

在配置文件中，你可以这样使用这个自定义过滤器：

spring:
  cloud:
    gateway:
      routes:
      - id: custom_filter_route
        uri: https://example.org
        filters:
        - CustomGatewayFilterFactory

这样配置后，所有通过这个路由的请求都会被添加一个名为"Custom-Header"的响应头，值为"MyValue"。