gateway 网关（转发，跨域，拦截器等）

1，所需依赖

<!-- 网关依赖 -->
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-gateway</artifactId>
</dependency>

2，配置路径映射

spring:
  cloud:
    gateway:
      discovery:
        locator:
          # 开启项目名称映射功能，即通过服务名访问项目，不需要写明具体IP地址
          enabled: true
          # 请求路由全部转小写字母，如 Aa/Bb 会被转为 aa/bb
          lower-case-service-id: true
      routes:
          # 路由规则的唯一标识，任意齐名，建议和服务名一致
        - id: sc-web-admin-back
          # 转发到的节点，lb:// 为 http，lb:ws:// 为 websocket
          uri: lb://sc-web-admin-back/
          predicates:
              # 断言规则，这里设置匹配的路由规则
            - Path=/admin-back/**
          # 过滤规则
          filters:
            # 转发到具体项目去掉路由首单词，如 /admin-back/a 转发为 /a
            - StripPrefix=1

如上，便配置了一个接管以 admin-back 开头的路由，并转发给项目 sc-web-admin-back

3，跨域配置

spring:
  cloud:
    gateway:
      globalcors:
        # 全局允许跨域访问
        cors-configurations:
          '[/**]':
            allow-credentials: true
            allowed-origins: "*"
            allowed-headers: "*"
            allowed-methods:
              - OPTIONS
              - GET
              - POST
              - PUT
              - DELETE

4，全局异常处理

日常开发中，我们难免会有忘记处理的异常，程序也很难保重不出错，这时候我们就需要一个能够全局捕捉异常的功能来未我们兜底，防止错误被用户看到影响体验

package com.hwq.gateway.handler;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.hwq.gateway.vo.ResultVO;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Primary;
import org.springframework.core.Ordered;
import org.springframework.core.annotation.Order;
import org.springframework.http.HttpStatus;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.stereotype.Component;
import org.springframework.web.server.ResponseStatusException;
import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.server.WebExceptionHandler;
import reactor.core.publisher.Mono;

@Component
@Primary   // 同类型带有该注解的 Bean 优先背识别
@Order(Ordered.HIGHEST_PRECEDENCE)
@Slf4j
public class JsonExceptionHandler implements WebExceptionHandler {

    @Autowired
    private ObjectMapper objectMapper;

    /**
     * 所有异常都会在这里被集中处理
     * @param exchange 上下文
     * @param ex       异常
     * SuppressWarnings("NullableProblems")：屏蔽 @NonNullApi 的警告
     */
    @Override
    @SuppressWarnings("NullableProblems")
    public Mono<Void> handle(ServerWebExchange exchange, Throwable ex) {
        ServerHttpResponse response = exchange.getResponse();
        ResultVO<Object> vo;
        if (ex instanceof ResponseStatusException && ((ResponseStatusException) ex).getStatus() == HttpStatus.NOT_FOUND) {
            vo = ResultVO.fail("当前访问的地址不存在，请修改后重试！");
        } else {
            vo = ResultVO.error(ex.getMessage());
        }
        return response.writeWith(Mono.fromSupplier(() -> {
            byte[] bytes;
            try {
                bytes = objectMapper.writeValueAsBytes(vo);
            } catch (JsonProcessingException e) {
                response.setStatusCode(HttpStatus.INTERNAL_SERVER_ERROR);
                bytes = "JSON 转换异常！".getBytes();
            }
            return response.bufferFactory().wrap(bytes);
        }));
    }

}

5，捕获转发项目传来的异常

上面的类只能捕捉网关本身发生的异常，而如果其调用（转发）的项目发生异常，返回错误时不能拦截，这时候我们就需要一个过滤器，能把哪些错误的返回拦截掉，并触发上面全局异常处理

package com.hwq.gateway.filter;

import org.reactivestreams.Publisher;
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.core.io.buffer.DataBufferUtils;
import org.springframework.http.HttpStatus;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.http.server.reactive.ServerHttpResponseDecorator;
import org.springframework.stereotype.Component;
import org.springframework.web.server.ResponseStatusException;
import org.springframework.web.server.ServerWebExchange;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import java.nio.charset.StandardCharsets;

@Component
public class ExceptionFilter implements Ordered, GlobalFilter {

    /**
     * 如果需要拦截返回值并处理，这里则需要返回负数
     */
    @Override
    public int getOrder() {
        return -1;
    }

    /**
     * 异常拦截，拦截响应值不是 200 的数据，并抛给全局异常处理
     */
    @Override
    @SuppressWarnings({"unchecked", "NullableProblems"})
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        ServerHttpResponse response = exchange.getResponse();
        ServerHttpResponseDecorator decorated = new ServerHttpResponseDecorator(response) {
            @Override
            public Mono<Void> writeWith(Publisher<? extends DataBuffer> body) {
                if (body instanceof Flux) {
                    Flux<? extends DataBuffer> fluxBody = (Flux<? extends DataBuffer>) body;
                    return super.writeWith(fluxBody.map(dataBuffer -> {
                        if (response.getStatusCode() == HttpStatus.NOT_FOUND) {
                            throw new ResponseStatusException(HttpStatus.NOT_FOUND);
                        }
                        if (response.getStatusCode() != HttpStatus.OK) {
                            byte[] content = new byte[dataBuffer.readableByteCount()];
                            dataBuffer.read(content);
                            DataBufferUtils.release(dataBuffer); // 释放掉内存
                            String errMsg = new String(content, StandardCharsets.UTF_8);
                            throw new RuntimeException(errMsg);
                        }
                        return dataBuffer;
                    }));
                }
                return super.writeWith(body);
            }
        };
        return chain.filter(exchange.mutate().response(decorated).build());
    }

}

6，普通的过滤器

package com.hwq.gateway.filter;

import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.core.Ordered;
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;

@Component
public class UserFilter implements Ordered, GlobalFilter {

    /**
     * 这里的返回值决定拦截器的优先级，数字越小越先被触发，支持负数
     */
    @Override
    public int getOrder() {
        return 1;
    }

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {

        // 这里可以获取 请求对象 和 响应对象
        ServerHttpRequest request = exchange.getRequest();
        ServerHttpResponse response = exchange.getResponse();

        // 逻辑处理
        

        // 逻辑处理

        // 传递给下一级别的过滤器
        return chain.filter(exchange);
    }
}