SpringCloud学习之Zuul统一异常处理及回退

　　其实在SpringCloud的Edgware SR2版本中对于ZuulFilter中的错误有统一的处理，但是在实际开发当中对于错误的响应方式，我想每个团队都有自己的处理规范。那么如何做到自定义的异常处理呢？

我们可以先参考一下SpringCloud提供的SendErrorFilter:

/*
 * Copyright 2013-2015 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.cloud.netflix.zuul.filters.post;

import javax.servlet.RequestDispatcher;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.cloud.netflix.zuul.util.ZuulRuntimeException;
import org.springframework.util.ReflectionUtils;
import org.springframework.util.StringUtils;

import com.netflix.zuul.ZuulFilter;
import com.netflix.zuul.context.RequestContext;
import com.netflix.zuul.exception.ZuulException;

import static org.springframework.cloud.netflix.zuul.filters.support.FilterConstants.ERROR_TYPE;
import static org.springframework.cloud.netflix.zuul.filters.support.FilterConstants.SEND_ERROR_FILTER_ORDER;

/**
 * Error {@link ZuulFilter} that forwards to /error (by default) if {@link RequestContext#getThrowable()} is not null.
 *
 * @author Spencer Gibb
 */
//TODO: move to error package in Edgware
public class SendErrorFilter extends ZuulFilter {

    private static final Log log = LogFactory.getLog(SendErrorFilter.class);
    protected static final String SEND_ERROR_FILTER_RAN = "sendErrorFilter.ran";

    @Value("${error.path:/error}")
    private String errorPath;

    @Override
    public String filterType() {
        return ERROR_TYPE;
    }

    @Override
    public int filterOrder() {
        return SEND_ERROR_FILTER_ORDER;
    }

    @Override
    public boolean shouldFilter() {
        RequestContext ctx = RequestContext.getCurrentContext();
        // only forward to errorPath if it hasn't been forwarded to already
        return ctx.getThrowable() != null
                && !ctx.getBoolean(SEND_ERROR_FILTER_RAN, false);
    }

    @Override
    public Object run() {
        try {
            RequestContext ctx = RequestContext.getCurrentContext();
            ZuulException exception = findZuulException(ctx.getThrowable());
            HttpServletRequest request = ctx.getRequest();

            request.setAttribute("javax.servlet.error.status_code", exception.nStatusCode);

            log.warn("Error during filtering", exception);
            request.setAttribute("javax.servlet.error.exception", exception);

            if (StringUtils.hasText(exception.errorCause)) {
                request.setAttribute("javax.servlet.error.message", exception.errorCause);
            }

            RequestDispatcher dispatcher = request.getRequestDispatcher(
                    this.errorPath);
            if (dispatcher != null) {
                ctx.set(SEND_ERROR_FILTER_RAN, true);
                if (!ctx.getResponse().isCommitted()) {
                    ctx.setResponseStatusCode(exception.nStatusCode);
                    dispatcher.forward(request, ctx.getResponse());
                }
            }
        }
        catch (Exception ex) {
            ReflectionUtils.rethrowRuntimeException(ex);
        }
        return null;
    }

    ZuulException findZuulException(Throwable throwable) {
        if (throwable.getCause() instanceof ZuulRuntimeException) {
            // this was a failure initiated by one of the local filters
            return (ZuulException) throwable.getCause().getCause();
        }

        if (throwable.getCause() instanceof ZuulException) {
            // wrapped zuul exception
            return (ZuulException) throwable.getCause();
        }

        if (throwable instanceof ZuulException) {
            // exception thrown by zuul lifecycle
            return (ZuulException) throwable;
        }

        // fallback, should never get here
        return new ZuulException(throwable, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, null);
    }

    public void setErrorPath(String errorPath) {
        this.errorPath = errorPath;
    }

}

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