SpringCloud gateway全局异常处理，以及后台的服务异常response的异常包装

gateway自己服务的全局异常处理，参考这篇https://segmentfault.com/a/1190000016854364?utm_source=tag-newest

有两个类

/**
 * @author wuweifeng wrote on 2018/11/2.
 */
@Configuration
public class ExceptionConfig {
    /**
     * 自定义异常处理[@@]注册Bean时依赖的Bean，会从容器中直接获取，所以直接注入即可
     */
    @Primary
    @Bean
    @Order(Ordered.HIGHEST_PRECEDENCE)
    public ErrorWebExceptionHandler errorWebExceptionHandler(ObjectProvider> viewResolversProvider,
                                                             ServerCodecConfigurer serverCodecConfigurer) {
        JsonExceptionHandler jsonExceptionHandler = new JsonExceptionHandler();
        jsonExceptionHandler.setViewResolvers(viewResolversProvider.getIfAvailable(Collections::emptyList));
        jsonExceptionHandler.setMessageWriters(serverCodecConfigurer.getWriters());
        jsonExceptionHandler.setMessageReaders(serverCodecConfigurer.getReaders());
        return jsonExceptionHandler;
    }
}

package com.maimeng.apigateway.config.exception;

/**
 * @author wuweifeng wrote on 2018/11/2.
 */

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.web.reactive.error.ErrorWebExceptionHandler;
import org.springframework.cloud.gateway.support.NotFoundException;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.codec.HttpMessageReader;
import org.springframework.http.codec.HttpMessageWriter;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.util.Assert;
import org.springframework.web.reactive.function.BodyInserters;
import org.springframework.web.reactive.function.server.RequestPredicates;
import org.springframework.web.reactive.function.server.RouterFunctions;
import org.springframework.web.reactive.function.server.ServerRequest;
import org.springframework.web.reactive.function.server.ServerResponse;
import org.springframework.web.reactive.result.view.ViewResolver;
import org.springframework.web.server.ResponseStatusException;
import org.springframework.web.server.ServerWebExchange;
import reactor.core.publisher.Mono;

import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * @classDesc: 统一异常处理, 参考{@link org.springframework.web.server.AbstractErrorWebExceptionHandler}修改
 * @author: chenggang
 */
public class JsonExceptionHandler implements ErrorWebExceptionHandler {

    private static final Logger log = LoggerFactory.getLogger(JsonExceptionHandler.class);

    /**
     * MessageReader
     */
    private List> messageReaders = Collections.emptyList();

    /**
     * MessageWriter
     */
    private List> messageWriters = Collections.emptyList();

    /**
     * ViewResolvers
     */
    private List viewResolvers = Collections.emptyList();

    /**
     * 存储处理异常后的信息
     */
    private ThreadLocal> exceptionHandlerResult = new ThreadLocal<>();

    /**
     * 参考AbstractErrorWebExceptionHandler
     */
    public void setMessageReaders(List> messageReaders) {
        Assert.notNull(messageReaders, "'messageReaders' must not be null");
        this.messageReaders = messageReaders;
    }

    /**
     * 参考AbstractErrorWebExceptionHandler
     */
    public void setViewResolvers(List viewResolvers) {
        this.viewResolvers = viewResolvers;
    }

    /**
     * 参考AbstractErrorWebExceptionHandler
     */
    public void setMessageWriters(List> messageWriters) {
        Assert.notNull(messageWriters, "'messageWriters' must not be null");
        this.messageWriters = messageWriters;
    }

    @Override
    public Mono handle(ServerWebExchange exchange, Throwable ex) {
        // 按照异常类型进行处理
        HttpStatus httpStatus;
        String body;
        if (ex instanceof NotFoundException) {
            httpStatus = HttpStatus.NOT_FOUND;
            body = "Service Not Found";
        } else if (ex instanceof ResponseStatusException) {
            ResponseStatusException responseStatusException = (ResponseStatusException) ex;
            httpStatus = responseStatusException.getStatus();
            body = responseStatusException.getMessage();
        } else {
            httpStatus = HttpStatus.INTERNAL_SERVER_ERROR;
            body = "Internal Server Error";
        }
        //封装响应体,此body可修改为自己的jsonBody
        Map result = new HashMap<>(2, 1);
        result.put("httpStatus", httpStatus);

        String msg = "{\"code\":" + httpStatus + ",\"message\": \"" + body + "\"}";
        result.put("body", msg);
        //错误记录
        ServerHttpRequest request = exchange.getRequest();
        log.error("[全局异常处理]异常请求路径:{},记录异常信息:{}", request.getPath(), ex.getMessage());
        //参考AbstractErrorWebExceptionHandler
        if (exchange.getResponse().isCommitted()) {
            return Mono.error(ex);
        }
        exceptionHandlerResult.set(result);
        ServerRequest newRequest = ServerRequest.create(exchange, this.messageReaders);
        return RouterFunctions.route(RequestPredicates.all(), this::renderErrorResponse).route(newRequest)
                .switchIfEmpty(Mono.error(ex))
                .flatMap((handler) -> handler.handle(newRequest))
                .flatMap((response) -> write(exchange, response));

    }

    /**
     * 参考DefaultErrorWebExceptionHandler
     */
    protected Mono renderErrorResponse(ServerRequest request) {
        Map result = exceptionHandlerResult.get();
        return ServerResponse.status((HttpStatus) result.get("httpStatus"))
                .contentType(MediaType.APPLICATION_JSON_UTF8)
                .body(BodyInserters.fromObject(result.get("body")));
    }

    /**
     * 参考AbstractErrorWebExceptionHandler
     */
    private Mono write(ServerWebExchange exchange,
                                       ServerResponse response) {
        exchange.getResponse().getHeaders()
                .setContentType(response.headers().getContentType());
        return response.writeTo(exchange, new ResponseContext());
    }

    /**
     * 参考AbstractErrorWebExceptionHandler
     */
    private class ResponseContext implements ServerResponse.Context {

        @Override
        public List> messageWriters() {
            return JsonExceptionHandler.this.messageWriters;
        }

        @Override
        public List viewResolvers() {
            return JsonExceptionHandler.this.viewResolvers;
        }

    }
}

那么gateway代理的后台服务，如果出现了异常没有处理，网关也是会直接原文返回给客户端的。

譬如在gateway后面有一个服务出了异常，当客户端请求时：

如果我们通用的返回值，并不是这么定义的，譬如我都是用code=200，message=xxx之类的json。那么当这样的返回值给客户端时，就会有问题了，因为不统一。而且我们无法保证网关后面的微服务都能捕获异常并返回统一的格式，所以，就需要在网关处做一层封装。对返回值、尤其是非正常的返回值做一个包装。

这一步的关键点就在于怎么获取服务的返回值。这个上一篇我们已经讲过了，https://blog.csdn.net/tianyaleixiaowu/article/details/83618037。

通过这篇文章获取到返回值后，可以通过判断json字符串是否包含code:xxx的字样，来判断后台的服务是否异常了。然后通过修改返回值，加上我们通用的返回值字段即可。