[学习交流] 【上海校区】网关 Spring-Cloud-Gateway 源码解析 —— 过滤器 (...

1. 概述

本文主要对过滤器 GatewayFilter 做整体的认识。

过滤器整体类图如下：

是不是有点疑惑 GlobalFilter 与 GatewayFilter 的关系？且见本文分晓。

推荐 Spring Cloud 视频：

2. GatewyFilter

org.springframework.cloud.gateway.filter.GatewayFilter ，网关过滤器接口，代码如下：

public interface GatewayFilter { /** * Process the Web request and (optionally) delegate to the next * {@code WebFilter} through the given {@link GatewayFilterChain}. * @param exchange the current server exchange * @param chain provides a way to delegate to the next filter * @return {@code Mono<Void>} to indicate when request processing is complete */ Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain);}

从接口方法可以看到，和 javax.servlet.Filter 类似。

GatewayFilter 有三种类型的子类实现，我们下面每节介绍一种。

2.1 GatewayFilterFactory 内部类

在每个 GatewayFilterFactory 实现类的 #apply(Tuple) 方法里，都声明了一个实现 GatewayFilter 的内部类，以 AddRequestHeaderGatewayFilterFactory 的代码举例子：

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: ServerHttpRequest request = exchange.getRequest().mutate()15: .header(name, value)16: .build();17: 18: return chain.filter(exchange.mutate().request(request).build());19: };20: }21: }

第 13 至 19 行：定义了一个 GatewayFilter 内部实现类。

在《Spring-Cloud-Gateway 源码解析 —— 过滤器 (4.2) 之 GatewayFilterFactory 过滤器工厂》，我们会详细解析每个 GatewayFilterFactory 定义的GatewayFilter 内部实现类。

2.2 OrderedGatewayFilter

org.springframework.cloud.gateway.filter.OrderedGatewayFilter ，有序的网关过滤器实现类。在 FilterChain 里，过滤器数组首先会按照 order 升序排序，按照顺序过滤请求。代码如下：

public class OrderedGatewayFilter implements GatewayFilter, Ordered { private final GatewayFilter delegate; private final int order; public OrderedGatewayFilter(GatewayFilter delegate, int order) { this.delegate = delegate; this.order = order; } @Override public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) { return this.delegate.filter(exchange, chain); } @Override public int getOrder() { return this.order; }}

delegate 属性，委托的 GatewayFilter 。
order 属性，顺序。
#filter(ServerWebExchange, GatewayFilterChain) 方法，使用 delegate 过滤请求。

2.3 GatewayFilterAdapter

org.springframework.cloud.gateway.handler.FilteringWebHandler.GatewayFilterAdapter ，网关过滤器适配器。在 GatewayFilterChain 使用 GatewayFilter 过滤请求，所以通过 GatewayFilterAdapter 将 GlobalFilter 适配成 GatewayFilter 。GatewayFilterAdapter 代码如下：

private static class GatewayFilterAdapter implements GatewayFilter { private final GlobalFilter delegate; public GatewayFilterAdapter(GlobalFilter delegate) { this.delegate = delegate; } @Override public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) { return this.delegate.filter(exchange, chain); }}

delegate 属性，委托的 GlobalFilter 。
#filter(ServerWebExchange, GatewayFilterChain) 方法，使用 delegate 过滤请求。

在 FilteringWebHandler 初始化时，将 GlobalFilter 委托成 GatewayFilterAdapter ，代码如下：

1: public class FilteringWebHandler implements WebHandler { 2: 3: /** 4: * 全局过滤器 5: */ 6: private final List<GatewayFilter> globalFilters; 7: 8: public FilteringWebHandler(List<GlobalFilter> globalFilters) { 9: this.globalFilters = loadFilters(globalFilters);10: }11: 12: private static List<GatewayFilter> loadFilters(List<GlobalFilter> filters) {13: return filters.stream()14: .map(filter -> {15: GatewayFilterAdapter gatewayFilter = new GatewayFilterAdapter(filter);16: if (filter instanceof Ordered) {17: int order = ((Ordered) filter).getOrder();18: return new OrderedGatewayFilter(gatewayFilter, order);19: }20: return gatewayFilter;21: }).collect(Collectors.toList());22: }23: }

第 16 至 19 行：当 GlobalFilter 子类实现了 org.springframework.core.Ordered 接口，在委托一层 OrderedGatewayFilter 。这样 AnnotationAwareOrderComparator#sort(List) 方法好排序。
第 20 行：当 GlobalFilter 子类没有实现了 org.springframework.core.Ordered 接口，在AnnotationAwareOrderComparator#sort(List) 排序时，顺序值为 Integer.MAX_VALUE 。
目前 GlobalFilter 都实现了 org.springframework.core.Ordered 接口。

3. GlobalFilter

org.springframework.cloud.gateway.filter.GlobalFilter ，全局过滤器接口，代码如下：

public interface GlobalFilter { /** * Process the Web request and (optionally) delegate to the next * {@code WebFilter} through the given {@link GatewayFilterChain}. * @param exchange the current server exchange * @param chain provides a way to delegate to the next filter * @return {@code Mono<Void>} to indicate when request processing is complete */ Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain);}

GlobalFilter 和 GatewayFilter 的 #filter(ServerWebExchange, GatewayFilterChain) 方法签名一致。官方说，未来的版本将作出一些调整。
FROM 《Spring Cloud Gateway》
This interface and usage are subject to change in future milestones
GlobalFilter 会作用到所有的 Route 上。

GlobalFilter 实现类如下类图：

RoutingFilter
- NettyRoutingFilter
- WebClientHttpRoutingFilter
- WebsocketRoutingFilter
- ForwardRoutingFilter
成对的 Filter
- NettyRoutingFilter / NettyRoutingFilter
- WebClientHttpRoutingFilter / WebClientWriteResponseFilter

梳理 GlobalFilter 的顺序如下：

TODO 【3030】

4. GatewayFilterChain

org.springframework.cloud.gateway.filter.GatewayFilterChain ，网关过滤器链接口。代码如下：

public interface GatewayFilterChain { /** * Delegate to the next {@code WebFilter} in the chain. * @param exchange the current server exchange * @return {@code Mono<Void>} to indicate when request handling is complete */ Mono<Void> filter(ServerWebExchange exchange);}

从接口方法可以看到，和 javax.servlet.FilterChain 类似。

org.springframework.cloud.gateway.handler.FilteringWebHandler.GatewayFilterAdapter ，网关过滤器链默认实现类。代码如下：

private static class DefaultGatewayFilterChain implements GatewayFilterChain { private int index; private final List<GatewayFilter> filters; public DefaultGatewayFilterChain(List<GatewayFilter> filters) { this.filters = filters; } @Override public Mono<Void> filter(ServerWebExchange exchange) { if (this.index < filters.size()) { GatewayFilter filter = filters.get(this.index++); return filter.filter(exchange, this); } else { return Mono.empty(); // complete } }}

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[学习交流] 【上海校区】网关 Spring-Cloud-Gateway 源码解析 —— 过滤器 (...

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