SpringCloud Finchley Gateway 统一异常处理

SpringCloud Finchley Gateway 统一异常处理

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• 1 . 问题：使用SpringCloud Gateway时，会出现各种系统级异常，默认返回HTML.
• 2 . Finchley版本的Gateway，使用WebFlux形式作为底层框架，而不是Servlet容器，所以常规的异常处理无法使用
• 翻阅源码，默认是使用DefaultErrorWebExceptionHandler这个类实现结构如下：

• 可以实现参考DefaultErrorWebExceptionHandler和AbstractErrorWebExceptionHandler自定义实现ErrorWebExceptionHandler，然后，注册为Bean到Spring容器中即可（Bean Name:"errorWebExceptionHandler"）
• 具体实现代码如下：

package pro.chenggang.example.spring.cloud.gateway.support;

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
 * @createTime: 2018/10/30
 */
public class JsonExceptionHandler implements ErrorWebExceptionHandler {

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

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

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

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

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

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

    /**
     * 参考AbstractErrorWebExceptionHandler
     * @param viewResolvers
     */
    public void setViewResolvers(List<ViewResolver> viewResolvers) {
        this.viewResolvers = viewResolvers;
    }

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

    @Override
    public Mono<Void> 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<String,Object> result = new HashMap<>(2,1);
        result.put("httpStatus",httpStatus);
        result.put("body",body);
        /**
         * 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
     * @param request
     * @return
     */
    protected Mono<ServerResponse> renderErrorResponse(ServerRequest request) {
        Map<String,Object> result = exceptionHandlerResult.get();
        return ServerResponse.status((HttpStatus) result.get("httpStatus"))
                .contentType(MediaType.APPLICATION_JSON_UTF8)
                .body(BodyInserters.fromObject(result.get("body")));
    }

    /**
     * 参考AbstractErrorWebExceptionHandler
     * @param exchange
     * @param response
     * @return
     */
    private Mono<? extends Void> 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<HttpMessageWriter<?>> messageWriters() {
            return JsonExceptionHandler.this.messageWriters;
        }

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

    }
}

• 注册Bean

    /**
     * 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
     * @param viewResolversProvider
     * @param serverCodecConfigurer
     * @return
     */
    @Primary
    @Bean
    @Order(Ordered.HIGHEST_PRECEDENCE)
    public ErrorWebExceptionHandler errorWebExceptionHandler(ObjectProvider<List<ViewResolver>> viewResolversProvider,
                                                             ServerCodecConfigurer serverCodecConfigurer) {

        JsonExceptionHandler jsonExceptionHandler = new JsonExceptionHandler();
        jsonExceptionHandler.setViewResolvers(viewResolversProvider.getIfAvailable(Collections::emptyList));
        jsonExceptionHandler.setMessageWriters(serverCodecConfigurer.getWriters());
        jsonExceptionHandler.setMessageReaders(serverCodecConfigurer.getReaders());
        log.debug("Init Json Exception Handler Instead Default ErrorWebExceptionHandler Success");
        return jsonExceptionHandler;
    }

• [@@]注意事项：

  • 1 .注册Bean时依赖的Bean，都会从Spring容器中获取到
  • 2 .参考此方法思路，可实现统一异常处理，统一封装错误信息。