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，對所有的請求生效，可以用來做權限控制，攔截到非法請求后如何返回自定義信息和將請求重定向到指定URL。

一、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）。

這里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", "鑒權失敗");
            byte[] bits = message.toJSONString().getBytes(StandardCharsets.UTF_8);
            DataBuffer buffer = response.bufferFactory().wrap(bits);
            response.setStatusCode(HttpStatus.UNAUTHORIZED);
            //指定編碼，否則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;
    }
}

　　

二、重定向(redirect)到指定頁面

對於瀏覽器，通常是發現沒有權限后跳轉到登錄頁面。響應狀態碼需要為HttpStatus.SEE_OTHER（303）。

重定向（redirect）會丟失之前請求的參數，對於需要轉發到目標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)到登錄頁面
        if (StringUtils.isBlank(token)) {
            String url = "http://想跳轉的網址";
            ServerHttpResponse response = exchange.getResponse();
            //303狀態碼表示由於請求對應的資源存在着另一個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;
    }
}