详解SpringCloud Gateway之过滤器GatewayFilter

/** * 网关过滤链表接口 * 用于过滤器的链式调用 * Contract to allow a {@link WebFilter} to delegate to the next in the chain. * * @author Rossen Stoyanchev * @since 5.0 */public interface GatewayFilterChain {  /**   * 链表启动调用入口方法   * 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);}

  /**   * 网关过滤的链表，用于过滤器的链式调用   * 过滤器链表接口的默认实现，   * 包含2个构建函数：   * 1.集合参数构建用于初始化吧构建链表   * 2. index，parent参数用于构建当前执行过滤对应的下次执行的链表    */  private static class DefaultGatewayFilterChain implements GatewayFilterChain {    /**     * 当前过滤执行过滤器在集合中索引     */    private final int index;    /**     * 过滤器集合     */    private final List<GatewayFilter> filters;    public DefaultGatewayFilterChain(List<GatewayFilter> filters) {      this.filters = filters;      this.index = 0;    }    /**     * 构建     * @param parent 上一个执行过滤器对应的FilterChain     * @param index 当前要执行过滤器的索引     */    private DefaultGatewayFilterChain(DefaultGatewayFilterChain parent, int index) {      this.filters = parent.getFilters();      this.index = index;    }    public List<GatewayFilter> getFilters() {      return filters;    }    /**     * @param exchange the current server exchange     * @return     */    @Override    public Mono<Void> filter(ServerWebExchange exchange) {      return Mono.defer(() -> {        if (this.index < filters.size()) {          //获取当前索引的过滤器          GatewayFilter filter = filters.get(this.index);          //构建当前索引的下一个过滤器的FilterChain          DefaultGatewayFilterChain chain = new DefaultGatewayFilterChain(this, this.index + 1);          //调用过滤器的filter方法执行过滤器          return filter.filter(exchange, chain);        } else {          //当前索引大于等于过滤集合大小，标识所有链表都已执行完毕，返回空          return Mono.empty(); // complete        }      });    }  }

/** * 网关路由过滤器， * Contract for interception-style, chained processing of Web requests that may * be used to implement cross-cutting, application-agnostic requirements such * as security, timeouts, and others. Specific to a Gateway * * Copied from WebFilter * * @author Rossen Stoyanchev * @since 5.0 */public interface GatewayFilter extends ShortcutConfigurable {  String NAME_KEY = "name";  String VALUE_KEY = "value";  /**   * 过滤器执行方法   * 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);}

/** * 排序的网关路由过滤器，用于包装真实的网关过滤器，已达到过滤器可排序 * @author Spencer Gibb */public class OrderedGatewayFilter implements GatewayFilter, Ordered {  //目标过滤器  private final GatewayFilter delegate;  //排序字段  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);  }}  

  /**   * 全局过滤器的包装类，将全局路由包装成统一的网关过滤器   */  private static class GatewayFilterAdapter implements GatewayFilter {    /**     * 全局过滤器     */    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);    }  }

    /**     * 全局过滤器，用户通过HttpClient转发请求     * @param httpClient     * @param headersFilters     * @return     */    @Bean    public NettyRoutingFilter routingFilter(HttpClient httpClient,                        ObjectProvider<List<HttpHeadersFilter>> headersFilters) {      return new NettyRoutingFilter(httpClient, headersFilters);    }    /**     * 全局的过滤器，用户将HttpClient客户端转发请求的响应写入到原始的请求响应中     * @param properties     * @return     */    @Bean    public NettyWriteResponseFilter nettyWriteResponseFilter(GatewayProperties properties) {      return new NettyWriteResponseFilter(properties.getStreamingMediaTypes());    }

  /**   * 全局过滤器，用于在通过负载均衡客户端选择服务实例信息   * @param client   * @return   */  @Bean  @ConditionalOnBean(LoadBalancerClient.class)  public LoadBalancerClientFilter loadBalancerClientFilter(LoadBalancerClient client) {    return new LoadBalancerClientFilter(client);  }

  /**   * 包装加载全局的过滤器，将全局过滤器包装成GatewayFilter   * @param filters   * @return   */  private static List<GatewayFilter> loadFilters(List<GlobalFilter> filters) {    return filters.stream()        .map(filter -> {          //将所有的全局过滤器包装成网关过滤器          GatewayFilterAdapter gatewayFilter = new GatewayFilterAdapter(filter);          //判断全局过滤器是否实现了可排序接口          if (filter instanceof Ordered) {            int order = ((Ordered) filter).getOrder();            //包装成可排序的网关过滤器            return new OrderedGatewayFilter(gatewayFilter, order);          }          return gatewayFilter;        }).collect(Collectors.toList());  }  @Override  public Mono<Void> handle(ServerWebExchange exchange) {    //获取请求上下文设置的路由实例    Route route = exchange.getRequiredAttribute(GATEWAY_ROUTE_ATTR);    //获取路由定义下的网关过滤器集合    List<GatewayFilter> gatewayFilters = route.getFilters();    //组合全局的过滤器与路由配置的过滤器    List<GatewayFilter> combined = new ArrayList<>(this.globalFilters);    //添加路由配置过滤器到集合尾部    combined.addAll(gatewayFilters);    //对过滤器进行排序    //TODO: needed or cached?    AnnotationAwareOrderComparator.sort(combined);    logger.debug("Sorted gatewayFilterFactories: "+ combined);    //创建过滤器链表对其进行链式调用    return new DefaultGatewayFilterChain(combined).filter(exchange);  }