Spring Cloud Gateway全局過濾器GlobalFilter：返回消息和重定向

Spring Cloud Gateway的全局過濾器GlobalFilter，顧名思義，聲明後會對全部的請求生效，能夠用來作權限控制，這裏簡單記錄一下攔截到非法請求後如何返回自定義信息和將請求重定向到指定URL。spring-cloud-gateway版本爲2.0.1.RELEASE。

1、返回401狀態碼和提示信息

只要將自定義的GlobalFilter聲明成Spring Bean就會自動生效，Ordered接口用來指定攔截器生效順序（數字越小優先級越高）。

這裏假設用來驗證權限的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狀態碼和提示信息
        if (StringUtils.isBlank(token)) {
            ServerHttpResponse response = exchange.getResponse();
            JSONObject message = new JSONObject();
            message.put("status", -1);
            message.put("data", "鑑權失敗");
            byte[] bits = message.toJSONString().getBytes(StandardCharsets.UTF_8);
            DataBuffer buffer = response.bufferFactory().wrap(bits);
            response.setStatusCode(HttpStatus.UNAUTHORIZED);
            //指定編碼，不然在瀏覽器中會中文亂碼
            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;
    }
}

2、重定向(redirect)到指定頁面

對於瀏覽器，一般是發現沒有權限後跳轉到登陸頁面。響應狀態碼須要爲HttpStatus.SEE_OTHER（303）。

重定向（redirect）會丟失以前請求的參數，對於須要轉發到目標URL的參數，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)到登陸頁面
        if (StringUtils.isBlank(token)) {
            String url = "http://想跳轉的網址";
            ServerHttpResponse response = exchange.getResponse();
            //303狀態碼錶示因爲請求對應的資源存在着另外一個URI，應使用GET方法定向獲取請求的資源
            response.setStatusCode(HttpStatus.SEE_OTHER);
            response.getHeaders().set(HttpHeaders.LOCATION, url);
            return response.setComplete();
        }
        return chain.filter(exchange);
    }

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