1.概述

网关在出错时，会有响应信息，我们有时需要自定义网关数据返回格式。我们可以通过扩展springgateway 来实现错误响应自定义。

2.实现代码

2.1 定义错误处理器

package com.redxun.gateway.exception;

import com.redxun.common.utils.SysPropertiesUtil;
import org.springframework.boot.autoconfigure.web.ErrorProperties;
import org.springframework.boot.autoconfigure.web.ResourceProperties;
import org.springframework.boot.autoconfigure.web.reactive.error.DefaultErrorWebExceptionHandler;
import org.springframework.boot.web.error.ErrorAttributeOptions;
import org.springframework.boot.web.reactive.error.ErrorAttributes;
import org.springframework.context.ApplicationContext;
import org.springframework.http.HttpStatus;
import org.springframework.security.oauth2.common.exceptions.InvalidTokenException;
import org.springframework.web.reactive.function.server.*;

import java.util.HashMap;
import java.util.Map;

/**
 * 自定义异常处理
 */
public class JsonErrorWebExceptionHandler extends DefaultErrorWebExceptionHandler {
    public JsonErrorWebExceptionHandler(ErrorAttributes errorAttributes, ResourceProperties resourceProperties,
                                        ErrorProperties errorProperties, ApplicationContext applicationContext) {
        super(errorAttributes, resourceProperties, errorProperties, applicationContext);
    }

    /**
     * 获取异常属性
     */
    @Override
    protected Map<String, Object> getErrorAttributes(ServerRequest request, ErrorAttributeOptions options) {
        Throwable error = super.getError(request);
        return responseError(request, error);
    }

    /**
     * 指定响应处理方法为JSON处理的方法
     * @param errorAttributes
     */
    @Override
    protected RouterFunction<ServerResponse> getRoutingFunction(ErrorAttributes errorAttributes) {
        return RouterFunctions.route(RequestPredicates.all(), this::renderErrorResponse);
    }

    /**
     * 根据code获取对应的HttpStatus
     * @param errorAttributes
     */
    @Override
    protected int getHttpStatus(Map<String, Object> errorAttributes) {
        Integer httpStatus = (Integer) errorAttributes.get("code");
        return httpStatus != null ? httpStatus : HttpStatus.INTERNAL_SERVER_ERROR.value();
    }

    /**
     * 构建异常信息
     * @param request
     * @param ex
     * @return
     */
    private String buildMessage(ServerRequest request, Throwable ex) {
        if(ex instanceof  InvalidTokenException){
            return ex.getMessage();
        }
        StringBuilder message = new StringBuilder("Failed to handle request [");
        message.append(request.methodName());
        message.append(" ");
        message.append(request.uri());
        message.append("]");
        if (ex != null) {
            message.append(": ");
            message.append(ex.getMessage());
        }
        return message.toString();
    }

    /**
     * 构建返回的JSON数据格式
     */
    private Map<String, Object> responseError(ServerRequest request, Throwable error) {
        String ctxPath= SysPropertiesUtil.getString("ctxPath");
        String errorMessage = buildMessage(request, error);
        int httpStatus = getHttpStatus(error);
        Map<String, Object> map = new HashMap<>();
        map.put("success", false);
        map.put("message", errorMessage);
        map.put("data", ctxPath);
        map.put("code", httpStatus);
        return map;
    }

    private int getHttpStatus(Throwable error) {
        int httpStatus;
        if (error instanceof InvalidTokenException) {
            InvalidTokenException ex = (InvalidTokenException)error;
            httpStatus = ex.getHttpErrorCode();
        } else {
            httpStatus = HttpStatus.INTERNAL_SERVER_ERROR.value();
        }
        return httpStatus;
    }
}

2.2 定义配置类

package com.redxun.gateway.exception;

import org.springframework.beans.factory.ObjectProvider;
import org.springframework.boot.autoconfigure.AutoConfigureBefore;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication;
import org.springframework.boot.autoconfigure.web.ResourceProperties;
import org.springframework.boot.autoconfigure.web.ServerProperties;
import org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.boot.web.reactive.error.ErrorAttributes;
import org.springframework.boot.web.reactive.error.ErrorWebExceptionHandler;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.Ordered;
import org.springframework.core.annotation.Order;
import org.springframework.http.codec.ServerCodecConfigurer;
import org.springframework.web.reactive.config.WebFluxConfigurer;
import org.springframework.web.reactive.result.view.ViewResolver;

import java.util.Collections;
import java.util.List;

/**
 * 自定义异常处理
 *
 */
@Configuration
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.REACTIVE)
@ConditionalOnClass(WebFluxConfigurer.class)
@AutoConfigureBefore(WebFluxAutoConfiguration.class)
@EnableConfigurationProperties({ServerProperties.class, ResourceProperties.class})
public class CustomErrorWebFluxAutoConfiguration {
    private final ServerProperties serverProperties;

    private final ApplicationContext applicationContext;

    private final ResourceProperties resourceProperties;

    private final List<ViewResolver> viewResolvers;

    private final ServerCodecConfigurer serverCodecConfigurer;

    public CustomErrorWebFluxAutoConfiguration(ServerProperties serverProperties,
                                               ResourceProperties resourceProperties,
                                               ObjectProvider<List<ViewResolver>> viewResolversProvider,
                                               ServerCodecConfigurer serverCodecConfigurer,
                                               ApplicationContext applicationContext) {
        this.serverProperties = serverProperties;
        this.applicationContext = applicationContext;
        this.resourceProperties = resourceProperties;
        this.viewResolvers = viewResolversProvider.getIfAvailable(Collections::emptyList);
        this.serverCodecConfigurer = serverCodecConfigurer;
    }

    @Bean
    @Order(Ordered.HIGHEST_PRECEDENCE)
    public ErrorWebExceptionHandler errorWebExceptionHandler(ErrorAttributes errorAttributes) {
        JsonErrorWebExceptionHandler exceptionHandler = new JsonErrorWebExceptionHandler(
                errorAttributes,
                this.resourceProperties,
                this.serverProperties.getError(),
                this.applicationContext);
        exceptionHandler.setViewResolvers(this.viewResolvers);
        exceptionHandler.setMessageWriters(this.serverCodecConfigurer.getWriters());
        exceptionHandler.setMessageReaders(this.serverCodecConfigurer.getReaders());
        return exceptionHandler;
    }
}

这样当网关出错时，就会响应我们自定义的错误信息。