Spring Cloud Gateway-自定义GatewayFilter

前提

GatewayFilter的作用域是指定的路由配置，路由配置选项里面需要通过filters指定想要使用的GatewayFilter列表。我们可以通过自定义GatewayFilter，做额外的扩展，实现一些内建GatewayFilter不存在的功能，并且应用到我们的路由配置中。

如何自定义GatewayFilter

需要定制GatewayFilter，则需要实现org.springframework.cloud.gateway.filter.factory.GatewayFilterFactory接口，GatewayFilterFactory的定义如下：

@FunctionalInterface
public interface GatewayFilterFactory<C> extends ShortcutConfigurable, Configurable<C> {

	String NAME_KEY = "name";

	String VALUE_KEY = "value";

	default GatewayFilter apply(Consumer<C> consumer) {
		C config = newConfig();
		consumer.accept(config);
		return apply(config);
	}

	default Class<C> getConfigClass() {
		throw new UnsupportedOperationException("getConfigClass() not implemented");
	}

	@Override
	default C newConfig() {
		throw new UnsupportedOperationException("newConfig() not implemented");
	}

	GatewayFilter apply(C config);

	default String name() {
		return NameUtils.normalizeFilterFactoryName(getClass());
	}

	@Deprecated
	default ServerHttpRequest.Builder mutate(ServerHttpRequest request) {
		return request.mutate();
	}
}  

public interface ShortcutConfigurable {

    default ShortcutType shortcutType() {
        return ShortcutType.DEFAULT;
    }

    default List<String> shortcutFieldOrder() {
        return Collections.emptyList();   
    }

    default String shortcutFieldPrefix() {
        return "";
    }    
}

public interface Configurable<C> {

	Class<C> getConfigClass();

	C newConfig();
}

看起来挺复杂的，但是实际上很多都是接口的默认方法，实际上要实现的方法很少。

另一种方式是继承org.springframework.cloud.gateway.filter.factory.AbstractGatewayFilterFactory，看抽象类AbstractGatewayFilterFactory的定义：

public abstract class AbstractGatewayFilterFactory<C> extends AbstractConfigurable<C>
		implements GatewayFilterFactory<C> {

	@SuppressWarnings("unchecked")
	public AbstractGatewayFilterFactory() {
		super((Class<C>) Object.class);
	}

	public AbstractGatewayFilterFactory(Class<C> configClass) {
		super(configClass);
	}

	public static class NameConfig {

		private String name;

		public String getName() {
			return name;
		}

		public void setName(String name) {
			this.name = name;
		}
	}
}

泛型参数C是配置类，从现有的AbstractGatewayFilterFactory或者GatewayFilterFactory的子类实现来看，配置类一般定义为公有静态内部类。

实现GatewayFilterFactory接口或者继承AbstractGatewayFilterFactory。
对应的子类注册到Spring的容器。
路由配置中的filters属性添加对应GatewayFilter配置，注意一下，过滤器名称由GatewayFilterFactory#name()决定。

实践

下面实现GatewayFilterFactory接口和继承AbstractGatewayFilterFactory抽象类两种方式都做了尝试。

实现GatewayFilterFactory接口

实现GatewayFilterFactory接口的时候，参考了SetRequestHeaderGatewayFilterFactory，为每个请求添加自定义的请求头。

@Component
public class CustomAddRequestHeaderGatewayFilterFactory implements
        GatewayFilterFactory<CustomAddRequestHeaderGatewayFilterFactory.CustomAddRequestHeaderConfig> {

    private final Class<CustomAddRequestHeaderConfig> configClass = CustomAddRequestHeaderConfig.class;

    @Override
    public List<String> shortcutFieldOrder() {
        return new ArrayList<>(Arrays.asList("headerName", "headerValue"));
    }

    @Override
    public GatewayFilter apply(CustomAddRequestHeaderConfig config) {
        return ((exchange, chain) -> {
            ServerHttpRequest request = exchange.getRequest().mutate().headers(httpHeaders -> {
                httpHeaders.set(config.getHeaderName(), config.getHeaderValue());
            }).build();
            return chain.filter(exchange.mutate().request(request).build());
        });
    }

    @Override
    public Class<CustomAddRequestHeaderConfig> getConfigClass() {
        return configClass;
    }

    @Override
    public CustomAddRequestHeaderConfig newConfig() {
        return BeanUtils.instantiateClass(this.configClass);
    }

    public static class CustomAddRequestHeaderConfig {

        private String headerName;
        private String headerValue;

        public String getHeaderName() {
            return headerName;
        }

        public void setHeaderName(String headerName) {
            this.headerName = headerName;
        }

        public String getHeaderValue() {
            return headerValue;
        }

        public void setHeaderValue(String headerValue) {
            this.headerValue = headerValue;
        }
    }
}

可以看到，其实最核心的功能操作是需要实现GatewayFilter apply(C config)方法，编写自定义的功能。注意这段Lambda表达式的逻辑：

return ((exchange, chain) -> {
    ServerHttpRequest request = exchange.getRequest().mutate().headers(httpHeaders -> {
        httpHeaders.set(config.getHeaderName(), config.getHeaderValue());
    }).build();
    return chain.filter(exchange.mutate().request(request).build());
});

其实，它可以简单理解为GatewayFilter接口的匿名实现。

application.yaml配置如下：

spring:
  cloud:
    gateway:
      routes:
        - id: custom_add_request_header_route
          uri: http://localhost:9091
          predicates:
            - Host=localhost:9090
          filters:
            - CustomAddRequestHeader=customHeaderName,customHeaderValue

为了配合测试，下游服务添加一个端点：

@GetMapping(value = "/customAddRequestHeader")
public ResponseEntity<String> customAddRequestHeader(@RequestHeader(name = "customHeaderName") String value) {
    return ResponseEntity.ok(value);
}

curl localhost:9090/order/customAddRequestHeader

// 响应
customHeaderValue

继承AbstractGatewayFilterFactory抽象类

继承AbstractGatewayFilterFactory的方式其实差不多，我们尝试做一个相对复杂的改造：对每一个请求成功(状态码为200)的响应，添加一个自定义的cookie和一个响应头。

@Component
public class CustomResponseGatewayFilterFactory extends
        AbstractGatewayFilterFactory<CustomResponseGatewayFilterFactory.Config> {

    public CustomResponseGatewayFilterFactory() {
        super(Config.class);
    }

    @Override
    public GatewayFilter apply(Config config) {
        return ((exchange, chain) -> {
            ServerHttpResponse response = exchange.getResponse();
            if (HttpStatus.OK.equals(response.getStatusCode())) {
                for (Map.Entry<String, String> entry : toMap(config.getCookie()).entrySet()) {
                    response.addCookie(ResponseCookie.from(entry.getKey(), entry.getValue()).build());
                }
                for (Map.Entry<String, String> entry : toMap(config.getHeader()).entrySet()) {
                    response.getHeaders().add(entry.getKey(), entry.getValue());
                }
                return chain.filter(exchange.mutate().response(response).build());
            } else {
                return chain.filter(exchange);
            }
        });
    }

    @Override
    public List<String> shortcutFieldOrder() {
        return Collections.singletonList(NAME_KEY);
    }

    private static Map<String, String> toMap(String value) {
        String[] split = value.split("=");
        Map<String, String> map = new HashMap<>(8);
        map.put(split[0], split[1]);
        return map;
    }

    public static class Config {

        private String cookie;
        private String header;

        public String getCookie() {
            return cookie;
        }

        public void setCookie(String cookie) {
            this.cookie = cookie;
        }

        public String getHeader() {
            return header;
        }

        public void setHeader(String header) {
            this.header = header;
        }
    }
}

application.yaml配置文件如下：

spring:
  cloud:
    gateway:
      routes:
        - id: custom_response_route
          uri: http://localhost:9091
          predicates:
            - Host=localhost:9090
          filters:
            - name: CustomResponse
              args:
                cookie: customCookieName=customCookieValue
                header: customHeaderName=customHeaderValue

这里注意，filters集合下的name属性是必须的，指向AbstractGatewayFilterFactory实现类的name()方法，args属性是用于指定装配到Config类的属性。

curl localhost:9090/order/remote

// 响应头如下
customHeaderName: customHeaderValue
Content-Type: text/plain;charset=UTF-8
Content-Length: 6
Date: Sun, 05 May 2019 11:06:35 GMT
set-cookie: customCookieName=customCookieValue