Spring Cloud Gateway的全局異常處理

Spring Cloud Gateway中的全局異常處理不能直接用@ControllerAdvice來處理，經過跟蹤異常信息的拋出，找到對應的源碼，自定義一些處理邏輯來符合業務的需求。

網關都是給接口作代理轉發的，後端對應的都是REST API，返回數據格式都是JSON。若是不作處理，當發生異常時，Gateway默認給出的錯誤信息是頁面，不方便前端進行異常處理。

須要對異常信息進行處理，返回JSON格式的數據給客戶端。下面先看實現的代碼，後面再跟你們講下須要注意的地方。

自定義異常處理邏輯：

package com.cxytiandi.gateway.exception;

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

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.reactive.error.ErrorAttributes;
import org.springframework.context.ApplicationContext;
import org.springframework.http.HttpStatus;
import org.springframework.web.reactive.function.server.RequestPredicates;
import org.springframework.web.reactive.function.server.RouterFunction;
import org.springframework.web.reactive.function.server.RouterFunctions;
import org.springframework.web.reactive.function.server.ServerRequest;
import org.springframework.web.reactive.function.server.ServerResponse;

/**
 * 自定義異常處理
 * 
 * <p>異常時用JSON代替HTML異常信息<p>
 * 
 * @author yinjihuan
 *
 */
public class JsonExceptionHandler extends DefaultErrorWebExceptionHandler {

    public JsonExceptionHandler(ErrorAttributes errorAttributes, ResourceProperties resourceProperties,
            ErrorProperties errorProperties, ApplicationContext applicationContext) {
        super(errorAttributes, resourceProperties, errorProperties, applicationContext);
    }

    /**
     * 獲取異常屬性
     */
    @Override
    protected Map<String, Object> getErrorAttributes(ServerRequest request, boolean includeStackTrace) {
        int code = 500;
        Throwable error = super.getError(request);
        if (error instanceof org.springframework.cloud.gateway.support.NotFoundException) {
            code = 404;
        }
        return response(code, this.buildMessage(request, error));
    }

    /**
     * 指定響應處理方法爲JSON處理的方法
     * @param errorAttributes
     */
    @Override
    protected RouterFunction<ServerResponse> getRoutingFunction(ErrorAttributes errorAttributes) {
        return RouterFunctions.route(RequestPredicates.all(), this::renderErrorResponse);
    }

    /**
     * 根據code獲取對應的HttpStatus
     * @param errorAttributes
     */
    @Override
    protected HttpStatus getHttpStatus(Map<String, Object> errorAttributes) {
        int statusCode = (int) errorAttributes.get("code");
        return HttpStatus.valueOf(statusCode);
    }

    /**
     * 構建異常信息
     * @param request
     * @param ex
     * @return
     */
    private String buildMessage(ServerRequest request, Throwable ex) {
        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();
    }

    /**
     * 構建返回的JSON數據格式
     * @param status        狀態碼
     * @param errorMessage  異常信息
     * @return
     */
    public static Map<String, Object> response(int status, String errorMessage) {
        Map<String, Object> map = new HashMap<>();
        map.put("code", status);
        map.put("message", errorMessage);
        map.put("data", null);
        return map;
    }

}

覆蓋默認的配置：

package com.cxytiandi.gateway.exception;

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

import org.springframework.beans.factory.ObjectProvider;
import org.springframework.boot.autoconfigure.web.ResourceProperties;
import org.springframework.boot.autoconfigure.web.ServerProperties;
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.result.view.ViewResolver;

/**
 * 覆蓋默認的異常處理
 * 
 * @author yinjihuan
 *
 */
@Configuration
@EnableConfigurationProperties({ServerProperties.class, ResourceProperties.class})
public class ErrorHandlerConfiguration {

    private final ServerProperties serverProperties;

    private final ApplicationContext applicationContext;

    private final ResourceProperties resourceProperties;

    private final List<ViewResolver> viewResolvers;

    private final ServerCodecConfigurer serverCodecConfigurer;

    public ErrorHandlerConfiguration(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) {
        JsonExceptionHandler exceptionHandler = new JsonExceptionHandler(
                errorAttributes, 
                this.resourceProperties,
                this.serverProperties.getError(), 
                this.applicationContext);
        exceptionHandler.setViewResolvers(this.viewResolvers);
        exceptionHandler.setMessageWriters(this.serverCodecConfigurer.getWriters());
        exceptionHandler.setMessageReaders(this.serverCodecConfigurer.getReaders());
        return exceptionHandler;
    }
    
}

注意點

• 異常時如何返回JSON而不是HTML?

在org.springframework.boot.autoconfigure.web.reactive.error.DefaultErrorWebExceptionHandler中的getRoutingFunction()方法就是控制返回格式的，原代碼以下：

@Override
protected RouterFunction<ServerResponse> getRoutingFunction(
            ErrorAttributes errorAttributes) {
       return RouterFunctions.route(acceptsTextHtml(), this::renderErrorView)
                .andRoute(RequestPredicates.all(), this::renderErrorResponse);
}

這邊優先是用HTML來顯示的，想用JSON的改下就能夠了，以下：

protected RouterFunction<ServerResponse> getRoutingFunction(ErrorAttributes errorAttributes) {
       return RouterFunctions.route(RequestPredicates.all(), this::renderErrorResponse);
}

• getHttpStatus須要重寫

原始的方法是經過status來獲取對應的HttpStatus的，代碼以下：

protected HttpStatus getHttpStatus(Map<String, Object> errorAttributes) {
      int statusCode = (int) errorAttributes.get("status");
      return HttpStatus.valueOf(statusCode);
}

若是咱們定義的格式中沒有status字段的話，這麼就會報錯，找不到對應的響應碼，要麼返回數據格式中增長status子段，要麼重寫，我這邊返回的是code，因此要重寫，代碼以下：

@Override
protected HttpStatus getHttpStatus(Map<String, Object> errorAttributes) {
    int statusCode = (int) errorAttributes.get("code");
    return HttpStatus.valueOf(statusCode);
}

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