1、首先自定义一个类，实现GlobalFilter和Ordered接口
2、重写filter和getOrder方法
3、在filter方法中，使用参数exchange获取请求对象和响应对象

ServerHttpRequest request = exchange.getRequest();
ServerHttpResponse response = exchange.getResponse();

4、使用请求对象request，分别获取请求的路径和请求参数中token的值

// 获取请求路径
String path = request.getPath().toString();
// 获取请求参数中token的值
String token = request.getQueryParams().getFirst("token");

5、定义静态常量

 private static final String PATH = "/login";
 private static final String CHARSET_NAME = "utf-8";
 private static final String ADMIN = "admin";

6、进行判断请求路径中是否有login或者请求参数token的值是否为admin

// 判断是否请求的login页面
if (path.contains(PATH)) {
    //  请求路径中含有/login,则放行
    return chain.filter(exchange);
        // 没有访问登录页面，判断请求参数中token的值是否为admin
        } else if(!token.isEmpty() && ADMIN.equals(token)){
            // 若请求参数token的值为admin，则放行
            return chain.filter(exchange);
        // 请求路径中没有login，并且请求参数的token的值不为admin，进行拦截
        } else {
            // 响应结果，响应数据为JSON数据
            HashMap data = new HashMap();
            DataBuffer buffer = null;
            try {
                data.put("code",404);
                data.put("msg","请先登录");

                byte[] bytes = JSON.toJSONString(data).getBytes(CHARSET_NAME);
                buffer = response.bufferFactory().wrap(bytes);
                response.setStatusCode(HttpStatus.UNAUTHORIZED);
                response.getHeaders().add("Content-Type","application/json;charset=UTF-8");
            }catch (Exception e) {
                e.printStackTrace();
            }
            return response.writeWith(Mono.just(buffer));
}

整体代码如下所示：

package com.lyq.apigateway.filter;

import com.alibaba.fastjson.JSON;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.core.Ordered;
import org.springframework.core.io.buffer.DataBuffer;
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 reactor.core.publisher.Mono;

import java.util.HashMap;

/**
 * @program: springcloud-nacos-077
 * @description: 全局过滤器
 * @author: Lv Yongqi
 * @create: 2021-07-08 19:10
 **/
@Component
public class AuthGlobalFilter implements GlobalFilter, Ordered {

    private static final String PATH = "/login";
    private static final String CHARSET_NAME = "utf-8";
    private static final String ADMIN = "admin";

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        ServerHttpRequest request = exchange.getRequest();
        ServerHttpResponse response = exchange.getResponse();

        // 获取请求路径，
        String path = request.getPath().toString();
        // 获取请求参数中token的值
        String token = request.getQueryParams().getFirst("token");
        // 判断是否请求的login页面
        if (path.contains(PATH)) {
            return chain.filter(exchange);
            // 没有访问登录页面，判断用户是否有token
        } else if(!token.isEmpty() && ADMIN.equals(token)){
            return chain.filter(exchange);
        } else {
            // 响应结果，
            HashMap data = new HashMap();
            DataBuffer buffer = null;
            try {
                data.put("code",404);
                data.put("msg","请先登录");

                byte[] bytes = JSON.toJSONString(data).getBytes(CHARSET_NAME);
                buffer = response.bufferFactory().wrap(bytes);
                response.setStatusCode(HttpStatus.UNAUTHORIZED);
                response.getHeaders().add("Content-Type","application/json;charset=UTF-8");
            }catch (Exception e) {
                e.printStackTrace();
            }
            return response.writeWith(Mono.just(buffer));
        }

    }

    /**
     * 权重，值越小优先级越高
     * @return
     */
    @Override
    public int getOrder() {
        return 0;
    }

}