1. 概述

本文主要分享 GatewayFilterFactory 的实现类。

GatewayFilterFactory 实现类较多，根据用途整理如下脑图：

下面我们开始逐块解析源码实现。

2. Header

本小节分享 Header 相关的 GatewayFilterFactory 实现类。

2.1 AddRequestHeaderGatewayFilterFactory

用途：添加指定请求 Header 为指定值。
配置：

spring:
  cloud:
    gateway:
      routes:
      # =====================================
      - id: add_request_header_route
        uri: http://example.org
        filters:
        - AddRequestHeader=X-Request-Foo, Bar

代码：

1: public class AddRequestHeaderGatewayFilterFactory implements GatewayFilterFactory {
 2: 
 3: 	@Override
 4: 	public List<String> argNames() {
 5: 		return Arrays.asList(NAME_KEY, VALUE_KEY);
 6: 	}
 7: 
 8: 	@Override
 9: 	public GatewayFilter apply(Tuple args) {
10: 		String name = args.getString(NAME_KEY);
11: 		String value = args.getString(VALUE_KEY);
12: 
13: 		return (exchange, chain) -> { // GatewayFilter
14: 			// 创建新的 ServerHttpRequest
15: 			ServerHttpRequest request = exchange.getRequest().mutate()
16: 					.header(name, value)
17: 					.build();
18: 
19: 			// 创建新的 ServerWebExchange ，提交过滤器链继续过滤
20: 			return chain.filter(exchange.mutate().request(request).build());
21: 		};
22: 	}
23: }

- uple 参数：name / value 。
第 14 至 17 行：创建新的 ServerHttpRequest 。
第 19 至 20 行：创建新的 ServerWebExchange ，提交过滤器链继续过滤。

2.2 RemoveRequestHeaderGatewayFilterFactory

类似 AddRequestHeaderGatewayFilterFactory ，不重复分享，点击《Spring Cloud Gateway —— RemoveRequestHeader GatewayFilter Factory》查看官方文档。

2.3 AddResponseHeaderGatewayFilterFactory

类似 AddRequestHeaderGatewayFilterFactory ，不重复分享，点击《Spring Cloud Gateway —— AddResponseHeader GatewayFilter Factory》查看官方文档。

2.4 RemoveResponseHeaderGatewayFilterFactory

类似 AddRequestHeaderGatewayFilterFactory ，不重复分享，点击《Spring Cloud Gateway —— RemoveResponseHeader GatewayFilter Factory》查看官方文档。

2.5 SetResponseHeaderGatewayFilterFactory

类似 AddRequestHeaderGatewayFilterFactory ，不重复分享，点击《Spring Cloud Gateway —— SetStatus GatewayFilter Factory》查看官方文档。

2.6 RemoveNonProxyHeadersGatewayFilterFactory

用途：移除请求 Proxy 相关的 Header 。默认值为 [ "Connection", "Keep-Alive", "Proxy-Authenticate", "Proxy-Authorization", "TE", "Trailer", "Transfer-Encoding", "Upgrade" ] ( 参考自：https://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-14#section-7.1.3 ) ，可以通过 spring.cloud.gateway.filter.remove-non-proxy-headers 配置。
代码：

1: @ConfigurationProperties("spring.cloud.gateway.filter.remove-non-proxy-headers")
 2: public class RemoveNonProxyHeadersGatewayFilterFactory implements GatewayFilterFactory {
 3: 
 4:     /**
 5:      * 默认
 6:      */
 7: 	public static final String[] DEFAULT_HEADERS_TO_REMOVE = new String[] {"Connection", "Keep-Alive",
 8: 			"Proxy-Authenticate", "Proxy-Authorization", "TE", "Trailer", "Transfer-Encoding", "Upgrade"};
 9: 
10: 	private List<String> headers = Arrays.asList(DEFAULT_HEADERS_TO_REMOVE);
11: 
12: 	public List<String> getHeaders() {
13: 		return headers;
14: 	}
15: 
16: 	public void setHeaders(List<String> headers) {
17: 		this.headers = headers;
18: 	}
19: 
20: 	@Override
21: 	public GatewayFilter apply(Tuple args) {
22: 		//TODO: support filter args
23: 
24: 		return (exchange, chain) -> {
25: 			// 创建新的 ServerHttpRequest
26: 			ServerHttpRequest request = exchange.getRequest().mutate()
27: 					.headers(httpHeaders -> {
28: 						for (String header : this.headers) {
29: 							httpHeaders.remove(header); // 移除
30: 						}
31: 					})
32: 					.build();
33: 
34: 			// 创建新的 ServerWebExchange ，提交过滤器链继续过滤
35: 			return chain.filter(exchange.mutate().request(request).build());
36: 		};
37: 	}
38:

2.7 SecureHeadersGatewayFilterFactory

用途：添加响应 Secure 相关的 Header 。默认值在 org.springframework.cloud.gateway.filter.factory.SecureHeadersProperties ，可以通过 spring.cloud.gateway.filter.secure-headers 配置。
推荐文章：
《Everything you need to know about HTTP security headers》
《4个常用的HTTP安全头部》
代码：

1: public class SecureHeadersGatewayFilterFactory implements GatewayFilterFactory {
 2: 
 3: 	public static final String X_XSS_PROTECTION_HEADER = "X-Xss-Protection";
 4: 	public static final String STRICT_TRANSPORT_SECURITY_HEADER = "Strict-Transport-Security";
 5: 	public static final String X_FRAME_OPTIONS_HEADER = "X-Frame-Options";
 6: 	public static final String X_CONTENT_TYPE_OPTIONS_HEADER = "X-Content-Type-Options";
 7: 	public static final String REFERRER_POLICY_HEADER = "Referrer-Policy";
 8: 	public static final String CONTENT_SECURITY_POLICY_HEADER = "Content-Security-Policy";
 9: 	public static final String X_DOWNLOAD_OPTIONS_HEADER = "X-Download-Options";
10: 	public static final String X_PERMITTED_CROSS_DOMAIN_POLICIES_HEADER = "X-Permitted-Cross-Domain-Policies";
11: 
12: 	private final SecureHeadersProperties properties;
13: 
14: 	public SecureHeadersGatewayFilterFactory(SecureHeadersProperties properties) {
15: 		this.properties = properties;
16: 	}
17: 
18: 	@Override
19: 	public GatewayFilter apply(Tuple args) {
20: 		//TODO: allow args to override properties
21: 
22: 		return (exchange, chain) -> {
23: 			HttpHeaders headers = exchange.getResponse().getHeaders();
24: 
25: 			//TODO: allow header to be disabled
26: 			headers.add(X_XSS_PROTECTION_HEADER, properties.getXssProtectionHeader());
27: 			headers.add(STRICT_TRANSPORT_SECURITY_HEADER, properties.getStrictTransportSecurity());
28: 			headers.add(X_FRAME_OPTIONS_HEADER, properties.getFrameOptions());
29: 			headers.add(X_CONTENT_TYPE_OPTIONS_HEADER, properties.getContentTypeOptions());
30: 			headers.add(REFERRER_POLICY_HEADER, properties.getReferrerPolicy());
31: 			headers.add(CONTENT_SECURITY_POLICY_HEADER, properties.getContentSecurityPolicy());
32: 			headers.add(X_DOWNLOAD_OPTIONS_HEADER, properties.getDownloadOptions());
33: 			headers.add(X_PERMITTED_CROSS_DOMAIN_POLICIES_HEADER, properties.getPermittedCrossDomainPolicies());
34: 
35: 			return chain.filter(exchange);
36: 		};
37: 	}
38: }

- 第 26 至 33 行：添加响应 Secure 相关的 Header 。

3. Parameter

本小节分享 Parameter 相关的 GatewayFilterFactory 实现类。

3.1 AddRequestParameterGatewayFilterFactory

类似 AddRequestHeaderGatewayFilterFactory ，不重复分享，点击《Spring Cloud Gateway —— AddRequestParameter GatewayFilter Factory》查看官方文档。

4. Path

本小节分享 Path 相关的 GatewayFilterFactory 实现类。

4.1 RewritePathGatewayFilterFactory

用途：根据配置的正则表达式 regexp ，使用配置的 replacement 重写请求 Path 。从功能目的上类似《Module ngx_http_rewrite_module》。
配置：

spring:
  cloud:
    gateway:
      routes:
      # =====================================
      - id: rewritepath_route
        uri: http://example.org
        predicates:
        - Path=/foo/**
        filters:
        - RewritePath=/foo/(?<segment>.*), /$\{segment}

- 注意，$\ 用于替代 $ ，避免和 YAML 语法冲突。
代码：

1: public class RewritePathGatewayFilterFactory implements GatewayFilterFactory {
 2: 
 3: 	public static final String REGEXP_KEY = "regexp";
 4: 	public static final String REPLACEMENT_KEY = "replacement";
 5: 
 6: 	@Override
 7: 	public List<String> argNames() {
 8: 		return Arrays.asList(REGEXP_KEY, REPLACEMENT_KEY);
 9: 	}
10: 
11: 	@Override
12: 	public GatewayFilter apply(Tuple args) {
13: 		final String regex = args.getString(REGEXP_KEY);
14: 		// `$\` 用于替代 `$` ，避免和 YAML 语法冲突。
15: 		String replacement = args.getString(REPLACEMENT_KEY).replace("$\\", "$");
16: 
17: 		return (exchange, chain) -> {
18: 			ServerHttpRequest req = exchange.getRequest();
19: 			// 添加 原始请求URI 到 GATEWAY_ORIGINAL_REQUEST_URL_ATTR
20: 			addOriginalRequestUrl(exchange, req.getURI());
21: 			// 重写 Path
22: 			String path = req.getURI().getPath();
23: 			String newPath = path.replaceAll(regex, replacement);
24: 
25: 			// 创建新的 ServerHttpRequest
26: 			ServerHttpRequest request = req.mutate()
27: 					.path(newPath) // 设置 Path
28: 					.build();
29: 
30: 			// 添加 请求URI 到 GATEWAY_REQUEST_URL_ATTR
31: 			exchange.getAttributes().put(GATEWAY_REQUEST_URL_ATTR, request.getURI());
32: 
33: 			// 创建新的 ServerWebExchange ，提交过滤器链继续过滤
34: 			return chain.filter(exchange.mutate().request(request).build());
35: 		};
36: 	}
37: }

Tuple 参数：regexp / replacement 。
第 15 行：$\ 用于替代 $ ，避免和 YAML 语法冲突。
第 20 行：调用 ServerWebExchangeUtils#addOriginalRequestUrl(...) 添加原始请求 URI 到 GATEWAY_ORIGINAL_REQUEST_URL_ATTR 。代码如下：

public static void addOriginalRequestUrl(ServerWebExchange exchange, URI url) {
		exchange.getAttributes().computeIfAbsent(GATEWAY_ORIGINAL_REQUEST_URL_ATTR, s -> new LinkedHashSet<>()); // 数组，考虑多次重写
    LinkedHashSet<URI> uris = exchange.getRequiredAttribute(GATEWAY_ORIGINAL_REQUEST_URL_ATTR);
    uris.add(url);
}

- - 为什么使用 LinkedHashSet ？因为可以使用 RewritePathGatewayFilterFactory / PrefixPathGatewayFilterFactory 多次重写。
第 21 至 23 行：重写请求 Path 。
第 26 至 28 行：创建新的 ServerHttpRequest 。
第 31 行：添加请求 URI 到 GATEWAY_REQUEST_URL_ATTR 。
第 34 行：创建新的 ServerWebExchange ，提交过滤器链继续过滤。

4.2 PrefixPathGatewayFilterFactory

类似 RewritePathGatewayFilterFactory ，不重复分享，点击《Spring Cloud Gateway —— PrefixPath GatewayFilter Factory》查看官方文档。

4.3 SetPathGatewayFilterFactory

类似 RewritePathGatewayFilterFactory ，不重复分享，点击《Spring Cloud Gateway —— SetPath GatewayFilter Factory》查看官方文档。

5. Status

本小节分享 Status 相关的 GatewayFilterFactory 实现类。

5.1 SetStatusGatewayFilterFactory

类似 RedirectToGatewayFilterFactory ，不重复分享，点击《Spring Cloud Gateway —— SetStatus GatewayFilter Factory》查看官方文档。

6. Redirect

本小节分享 Redirect 相关的 GatewayFilterFactory 实现类。

6.1 RedirectToGatewayFilterFactory

用途：将响应重定向到指定 URL ，并设置响应状态码为指定 Status 。注意，Status 必须为 3XX 重定向状态码。
配置：

spring:
  cloud:
    gateway:
      routes:
      # =====================================
      - id: prefixpath_route
        uri: http://example.org
        filters:
        - RedirectTo=302, http://www.iocoder.cn

代码：

1: public class RedirectToGatewayFilterFactory implements GatewayFilterFactory {
 2: 
 3: 	public static final String STATUS_KEY = "status";
 4: 	public static final String URL_KEY = "url";
 5: 
 6: 	@Override
 7: 	public List<String> argNames() {
 8: 		return Arrays.asList(STATUS_KEY, URL_KEY);
 9: 	}
10: 
11: 	@Override
12: 	public GatewayFilter apply(Tuple args) {
13: 		String statusString = args.getRawString(STATUS_KEY);
14: 		String urlString = args.getString(URL_KEY);
15: 
16: 		// 解析 status ，并判断是否是 3XX 重定向状态
17: 		final HttpStatus httpStatus = parse(statusString);
18: 		Assert.isTrue(httpStatus.is3xxRedirection(), "status must be a 3xx code, but was " + statusString);
19: 		// 创建 URL
20: 		final URL url;
21: 		try {
22: 			url = URI.create(urlString).toURL();
23: 		} catch (MalformedURLException e) {
24: 			throw new IllegalArgumentException("Invalid url " + urlString, e);
25: 		}
26: 
27: 		return (exchange, chain) ->
28: 			chain.filter(exchange).then(Mono.defer(() -> { // After Filter
29: 				if (!exchange.getResponse().isCommitted()) {
30: 				    // 设置响应 Status
31: 					setResponseStatus(exchange, httpStatus);
32: 
33: 					// 设置响应 Header
34: 					final ServerHttpResponse response = exchange.getResponse();
35: 					response.getHeaders().set(HttpHeaders.LOCATION, url.toString());
36: 					return response.setComplete();
37: 				}
38: 				return Mono.empty();
39: 			}));
40: 	}
41: 
42: }

- 第 16 至 18 行：解析配置的 statusString ，并判断是否是 3XX 重定向状态码。
第 19 至 25 行：解析配置的 urlString ，创建 URL 。
第 28 行：调用 #then(Mono) 方法，实现 After Filter 逻辑。这里和 AddRequestHeaderGatewayFilterFactory 实现的 Before Filter 【方式】不同。
第 29 至 37 行：若响应未提交，设置响应的状态码、响应的 Header ( Location ) 。
第 38 行：设置响应已提交。

7. Hystrix

熔断相关 GatewayFilter，我们在《Spring-Cloud-Gateway 源码解析 —— 过滤器 (4.9) 之 HystrixGatewayFilterFactory 熔断》详细解析。

8. RateLimiter

限流相关 GatewayFilter，我们在《Spring-Cloud-Gateway 源码解析 —— 过滤器 (4.10) 之 RequestRateLimiterGatewayFilterFactory 请求限流》详细解析。

Spring-Cloud-Gateway 源码解析 —— 过滤器 (4.2) 之 GatewayFilterFactory 过滤器工厂