如何实现Spring Cloud Zuul路由网关服务过滤

<dependency>
  <groupId>org.springframework.cloud</groupId>
  <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
</dependency>
<dependency>
  <groupId>org.springframework.cloud</groupId>
  <artifactId>spring-cloud-starter-netflix-zuul</artifactId>
</dependency>

zuul:
 routes:
  api-a:
   path: /api/ribbon/**
   serviceId: hello-spring-cloud-web-admin-ribbon
  api-b:
   path: /api/feign/**
   serviceId: hello-spring-cloud-web-admin-feign

@SpringBootApplication
@EnableEurekaClient
@EnableZuulProxy
public class ZuulApplication {
  public static void main(String[] args) {
    SpringApplication.run(ZuulApplication.class, args);
  }
}

/**
 * 路由 hello-spring-cloud-web-admin-feign 失败时的回调
 */
@Component
public class WebAdminFeignFallbackProvider implements FallbackProvider {

  @Override
  public String getRoute() {
    // ServiceId，如果需要所有调用都支持回退，则 return "*" 或 return null
    return "hello-spring-cloud-web-admin-feign";
  }

  /**
   * 如果请求服务失败，则返回指定的信息给调用者
   * @param route
   * @param cause
   * @return
   */
  @Override
  public ClientHttpResponse fallbackResponse(String route, Throwable cause) {
    return new ClientHttpResponse() {
      /**
       * 网关向 api 服务请求失败了，但是消费者客户端向网关发起的请求是成功的，
       * 不应该把 api 的 404,500 等问题抛给客户端
       * 网关和 api 服务集群对于客户端来说是黑盒
       * @return
       * @throws IOException
       */
      @Override
      public HttpStatus getStatusCode() throws IOException {
        return HttpStatus.OK;
      }

      @Override
      public int getRawStatusCode() throws IOException {
        return HttpStatus.OK.value();
      }

      @Override
      public String getStatusText() throws IOException {
        return HttpStatus.OK.getReasonPhrase();
      }

      @Override
      public void close() {

      }

      @Override
      public InputStream getBody() throws IOException {
        ObjectMapper objectMapper = new ObjectMapper();
        Map<String, Object> map = new HashMap<>();
        map.put("status", 200);
        map.put("message", "无法连接");
        return new ByteArrayInputStream(objectMapper.writeValueAsString(map).getBytes("UTF-8"));
      }

      @Override
      public HttpHeaders getHeaders() {
        HttpHeaders headers = new HttpHeaders();
        // 和 getBody 中的内容编码一致
        headers.setContentType(MediaType.APPLICATION_JSON_UTF8);
        return headers;
      }
    };
  }
}

/**
 * Zuul 的服务过滤演示
 */
@Component
public class LoginFilter extends ZuulFilter {

  private static final Logger logger = LoggerFactory.getLogger(LoginFilter.class);

  /**
   * 配置过滤类型，有四种不同生命周期的过滤器类型
   * 1. pre：路由之前
   * 2. routing：路由之时
   * 3. post：路由之后
   * 4. error：发送错误调用
   * @return
   */
  @Override
  public String filterType() {
    return "pre";
  }

  /**
   * 配置过滤的顺序
   * @return
   */
  @Override
  public int filterOrder() {
    return 0;
  }

  /**
   * 配置是否需要过滤：true/需要，false/不需要
   * @return
   */
  @Override
  public boolean shouldFilter() {
    return true;
  }

  /**
   * 过滤器的具体业务代码
   * @return
   * @throws ZuulException
   */
  @Override
  public Object run() throws ZuulException {
    RequestContext context = RequestContext.getCurrentContext();
    HttpServletRequest request = context.getRequest();
    String token = request.getParameter("token");
    if (token == null) {
      logger.warn("Token is empty");
      context.setSendZuulResponse(false);
      context.setResponseStatusCode(401);
      try {
        context.getResponse().getWriter().write("Token is empty");
      } catch (IOException e) {
      }
    } else {
      logger.info("OK");
    }
    return null;
  }
}