Spring Cloud Gateway全局过滤器GlobalF

Spring Cloud Gateway的全局过滤器GlobalFilter，对所有的请求生效，可以用来做权限控制，拦截到非法请求后如何返回自定义信息和将请求重定向到指定URL。

一、返回401状态码和提示信息
只要将自定义的GlobalFilter声明成Spring Bean就会自动生效，Ordered接口用来指定拦截器生效顺序（数字越小优先级越高）。

这里假设用来验证权限的key是authToken。

import java.net.URI;
import java.nio.charset.StandardCharsets;

import org.apache.commons.lang3.StringUtils;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.cloud.gateway.support.ServerWebExchangeUtils;
import org.springframework.core.Ordered;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.stereotype.Component;
import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.util.UriComponentsBuilder;

import com.alibaba.fastjson.JSONObject;

@Component
public class AuthFilter implements GlobalFilter, Ordered {

   @Override
   public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
       String token = exchange.getRequest().getQueryParams().getFirst("authToken");
       //返回401状态码和提示信息
       if (StringUtils.isBlank(token)) {
           ServerHttpResponse response = exchange.getResponse();
           JSONObject message = new JSONObject();
           message.put("status", -1);
           message.put("data", "鉴权失败");
           byte[] bits = message.toJSONString().getBytes(StandardCharsets.UTF_8);
           DataBuffer buffer = response.bufferFactory().wrap(bits);
           response.setStatusCode(HttpStatus.UNAUTHORIZED);
           //指定编码，否则在浏览器中会中文乱码
           response.getHeaders().add("Content-Type", "text/plain;charset=UTF-8");
           return response.writeWith(Mono.just(buffer));
       }
       return chain.filter(exchange);
   }

   @Override
   public int getOrder() {
       return -100;
   }
}

二、重定向(redirect)到指定页面
对于浏览器，通常是发现没有权限后跳转到登录页面。响应状态码需要为HttpStatus.SEE_OTHER（303）。

重定向（redirect）会丢失之前请求的参数，对于需要转发到目标URL的参数，需手工添加。

import java.net.URI;
import java.nio.charset.StandardCharsets;

import org.apache.commons.lang3.StringUtils;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.cloud.gateway.support.ServerWebExchangeUtils;
import org.springframework.core.Ordered;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.stereotype.Component;
import org.springframework.web.server.ServerWebExchange;

@Component
public class AuthFilter implements GlobalFilter, Ordered {

   @Override
   public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
       String token = exchange.getRequest().getQueryParams().getFirst("authToken");
       //重定向(redirect)到登录页面
       if (StringUtils.isBlank(token)) {
           String url = "http://想跳转的网址";
           ServerHttpResponse response = exchange.getResponse();
           //303状态码表示由于请求对应的资源存在着另一个URI，应使用GET方法定向获取请求的资源
           response.setStatusCode(HttpStatus.SEE_OTHER);
           response.getHeaders().set(HttpHeaders.LOCATION, url);
           return response.setComplete();
       }
       return chain.filter(exchange);
   }

   @Override
   public int getOrder() {
       return -100;
   }
}