自定义Filter

说明

• 本文介绍如何对 org.springframework.web.server.WebFliter 进行扩展。

跨域支持

• 新增 org.apache.shenyu.web.filter.CrossFilter 实现 WebFilter。

  ``` public class CrossFilter implements WebFilter {

    private static final String ALLOWED_HEADERS = "x-requested-with, authorization, Content-Type, Authorization, credential, X-XSRF-TOKEN,token,username,client";
    private static final String ALLOWED_METHODS = "*";
    private static final String ALLOWED_ORIGIN = "*";
    private static final String ALLOWED_EXPOSE = "*";
    private static final String MAX_AGE = "18000";
    @Override
    @SuppressWarnings("all")
    public Mono<Void> filter(final ServerWebExchange exchange, final WebFilterChain chain) {
        ServerHttpRequest request = exchange.getRequest();
        if (CorsUtils.isCorsRequest(request)) {
            ServerHttpResponse response = exchange.getResponse();
            HttpHeaders headers = response.getHeaders();
            headers.add("Access-Control-Allow-Origin", ALLOWED_ORIGIN);
            headers.add("Access-Control-Allow-Methods", ALLOWED_METHODS);
            headers.add("Access-Control-Max-Age", MAX_AGE);
            headers.add("Access-Control-Allow-Headers", ALLOWED_HEADERS);
            headers.add("Access-Control-Expose-Headers", ALLOWED_EXPOSE);
            headers.add("Access-Control-Allow-Credentials", "true");
            if (request.getMethod() == HttpMethod.OPTIONS) {
                response.setStatusCode(HttpStatus.OK);
                return Mono.empty();
            }
        }
        return chain.filter(exchange);
    }
}
```

* 将 `CrossFilter` 注册成为 `Spring`的`bean`。
## 网关过滤 springboot健康检查
* 注意顺序，使用 `@Order` 注解
```java
@Component
@Order(-99)
public final class HealthFilter implements WebFilter {
    private static final String[] FILTER_TAG = {"/actuator/health", "/health_check"};
    @Override
    public Mono<Void> filter(@Nullable final ServerWebExchange exchange, @Nullable final WebFilterChain chain) {
        ServerHttpRequest request = Objects.requireNonNull(exchange).getRequest();
        String urlPath = request.getURI().getPath();
        for (String check : FILTER_TAG) {
            if (check.equals(urlPath)) {
                String result = JsonUtils.toJson(new Health.Builder().up().build());
                DataBuffer dataBuffer = exchange.getResponse().bufferFactory().wrap(result.getBytes());
                return exchange.getResponse().writeWith(Mono.just(dataBuffer));
            }
        }
        return Objects.requireNonNull(chain).filter(exchange);
    }
}

继承 org.apache.shenyu.web.filter.AbstractWebFilter

• 新增一个类继承AbstractWebFilter，并实现它的两个方法。

   /**
     * this is Template Method ,children Implement your own filtering logic.
     *
     * @param exchange the current server exchange
     * @param chain    provides a way to delegate to the next filter
     * @return {@code Mono<Boolean>} result：TRUE (is pass)，and flow next filter；FALSE (is not pass) execute doDenyResponse(ServerWebExchange exchange)
     */
    protected abstract Mono<Boolean> doFilter(ServerWebExchange exchange, WebFilterChain chain);
    /**
     * this is Template Method ,children Implement your own And response client.
     *
     * @param exchange the current server exchange.
     * @return {@code Mono<Void>} response msg.
     */
    protected abstract Mono<Void> doDenyResponse(ServerWebExchange exchange);

• doFilter 方法返回 Mono<true> 表示通过，反之则不通过，不通过的时候，会调用 doDenyResponse输出相关信息到前端。