zuul 1.x 是如何实现请求转发的
文档写的再好，也不如源码写的好
源码地址：
GitHub: https://github.com/Netflix/zuul
Gitee: https://gitee.com/github_mirror_plus/zuul
目录
- 简介
- 实现逻辑
- 源码
- 基于 Servlet 的请求转发
- ZuulServlet 核心代码
- ZuulRunner 核心代码
- RequestContext 核心代码
- FilterProcessor 核心代码
- 在官方示例中，提供了两个简单的 Route 的 ZuulFilter 实现
- 总结
- 参考
简介
官方简介，其实你要看这篇，说明你知道 zuul
Zuul is an edge service that provides dynamic routing, monitoring, resiliency, security, and more. Please view the wiki for usage, information, HOWTO, etc https://github.com/Netflix/zuul/wiki
Here are some links to help you learn more about the Zuul Project. Feel free to PR to add any other info, presentations, etc.
实现逻辑
上一篇文章 Go | Go 结合 Consul 实现动态反向代理 里面简单的实现了一个反向代理，并简述了一下步骤，这里复述一下
根据代理的描述一共分成几个步骤：
- 代理接收到客户端的请求，复制了原来的请求对象
- 根据一些规则，修改新请求的请求指向
- 把新请求发送到根据服务器端，并接收到服务器端返回的响应
- 将上一步的响应根据需求处理一下，然后返回给客户端
源码
注意：这里的源码指的是 1.x 分支的代码
基于 Servlet 的请求转发
在一开始学习 Java Web 时，Servlet 是一个绕不过去的坎，zuul 也是基于 Servlet 实现的，在源码
<?在这里需要重点关注下 com.netflix.zuul.http.ZuulServlet 和 com.netflix.zuul.context.ContextLifecycleFilter
ZuulServlet 核心代码
代码在 com.netflix.zuul.http.ZuulServlet
下面的代码中省略了一部分，在这个过程中主要做了以下几件事
- 将 将原始的 Request，Response 保存在 ThreadLocal 中，方便以后处理。因为 Tomcat 等 Servlet 容器默认使用了一个请求一个线程处理的方式，所以存在 ThreadLocal 即可在以后的处理流程中方便处理
- 执行前置过滤器
preRoute() - 执行转发中过滤器
route() - 执行后置过滤器
postRoute()
其中转发的关键就在 route() 方法
public class ZuulServlet extends HttpServlet { private ZuulRunner zuulRunner; @Override public void service(javax.servlet.ServletRequest servletRequest, javax.servlet.ServletResponse servletResponse) throws ServletException, IOException { try { // 这一步是将原始的 Request，Response 保存在 ThreadLocal 中 init((HttpServletRequest) servletRequest, (HttpServletResponse) servletResponse); RequestContext context = RequestContext.getCurrentContext(); context.setZuulEngineRan(); try { // 前置处理 preRoute(); } catch (ZuulException e) { error(e); postRoute(); return; } try { // 转发中处理 route(); } catch (ZuulException e) { error(e); postRoute(); return; } try { // 后置处理 postRoute(); } catch (ZuulException e) { // 异常处理 error(e); return; } } catch (Throwable e) { error(new ZuulException(e, 500, "UNHANDLED_EXCEPTION_" + e.getClass().getName())); } finally { RequestContext.getCurrentContext().unset(); } } void postRoute() throws ZuulException { zuulRunner.postRoute(); } void route() throws ZuulException { zuulRunner.route(); } void preRoute() throws ZuulException { zuulRunner.preRoute(); } void init(HttpServletRequest servletRequest, HttpServletResponse servletResponse) { zuulRunner.init(servletRequest, servletResponse); } void error(ZuulException e) { RequestContext.getCurrentContext().setThrowable(e); zuulRunner.error(); }}ZuulRunner 核心代码
从上面的代码可以看出转发的关键在于 ZuulServlet#route()， 而 ZuulServlet#route() 在于 zuulRunner.route()
ZuulRunner 主要功能
init将 Request 和 Response 保存到RequestContext.getCurrentContext(), 这里面就是上面提到的ThreadLocal的处理类- 调用下
FilterProcessor.getInstance().route()
public class ZuulRunner { private boolean bufferRequests; public ZuulRunner() { this.bufferRequests = true; } public ZuulRunner(boolean bufferRequests) { this.bufferRequests = bufferRequests; } public void init(HttpServletRequest servletRequest, HttpServletResponse servletResponse) { RequestContext ctx = RequestContext.getCurrentContext(); if (bufferRequests) { ctx.setRequest(new HttpServletRequestWrapper(servletRequest)); } else { ctx.setRequest(servletRequest); } ctx.setResponse(new HttpServletResponseWrapper(servletResponse)); } public void route() throws ZuulException { FilterProcessor.getInstance().route(); }}RequestContext 核心代码
主要是 ThreadLocal 和 copy
public class RequestContext extends ConcurrentHashMap<String, Object> { private static final Logger LOG = LoggerFactory.getLogger(RequestContext.class); protected static Class<? extends RequestContext> contextClass = RequestContext.class; private static RequestContext testContext = null; protected static final ThreadLocal<? extends RequestContext> threadLocal = new ThreadLocal<RequestContext>() { @Override protected RequestContext initialValue() { try { return contextClass.newInstance(); } catch (Throwable e) { throw new RuntimeException(e); } } }; /** * sets the "responseBody" value as a String. This is the response sent back to the client. * * @param body */ public void setResponseBody(String body) { set("responseBody", body); } /** * Use this instead of response.setStatusCode() * * @param nStatusCode */ public void setResponseStatusCode(int nStatusCode) { getResponse().setStatus(nStatusCode); set("responseStatusCode", nStatusCode); } /** * Mkaes a copy of the RequestContext. This is used for debugging. * * @return */ public RequestContext copy() { RequestContext copy = new RequestContext(); // 这里省略了一部分代码，意思就是把原来的 request 深度复制一份 return copy; }}FilterProcessor 核心代码
主要逻辑就是找到对应 type 的 List<ZuulFilter> 并执行 runFilter()
public class FilterProcessor { static FilterProcessor INSTANCE = new FilterProcessor(); /** * @return the singleton FilterProcessor */ public static FilterProcessor getInstance() { return INSTANCE; } /** * Runs all "route" filters. These filters route calls to an origin. * * @throws ZuulException if an exception occurs. */ public void route() throws ZuulException { try { runFilters("route"); } catch (ZuulException e) { throw e; } catch (Throwable e) { throw new ZuulException(e, 500, "UNCAUGHT_EXCEPTION_IN_ROUTE_FILTER_" + e.getClass().getName()); } } /** * runs all filters of the filterType sType/ Use this method within filters to run custom filters by type * * @param sType the filterType. * @return * @throws Throwable throws up an arbitrary exception */ public Object runFilters(String sType) throws Throwable { if (RequestContext.getCurrentContext().debugRouting()) { Debug.addRoutingDebug("Invoking {" + sType + "} type filters"); } boolean bResult = false; List<ZuulFilter> list = FilterLoader.getInstance().getFiltersByType(sType); if (list != null) { for (int i = 0; i < list.size(); i++) { ZuulFilter zuulFilter = list.get(i); Object result = processZuulFilter(zuulFilter); if (result != null && result instanceof Boolean) { bResult |= ((Boolean) result); } } } return bResult; } /** * Processes an individual ZuulFilter. This method adds Debug information. Any uncaught Thowables are caught by this method and converted to a ZuulException with a 500 status code. * * @param filter * @return the return value for that filter * @throws ZuulException */ public Object processZuulFilter(ZuulFilter filter) throws ZuulException { RequestContext ctx = RequestContext.getCurrentContext(); boolean bDebug = ctx.debugRouting(); final String metricPrefix = "zuul.filter-"; long execTime = 0; String filterName = ""; try { long ltime = System.currentTimeMillis(); filterName = filter.getClass().getSimpleName(); RequestContext copy = null; Object o = null; Throwable t = null; if (bDebug) { Debug.addRoutingDebug("Filter " + filter.filterType() + " " + filter.filterOrder() + " " + filterName); copy = ctx.copy(); } ZuulFilterResult result = filter.runFilter(); ExecutionStatus s = result.getStatus(); execTime = System.currentTimeMillis() - ltime; switch (s) { case FAILED: t = result.getException(); ctx.addFilterExecutionSummary(filterName, ExecutionStatus.FAILED.name(), execTime); break; case SUCCESS: o = result.getResult(); ctx.addFilterExecutionSummary(filterName, ExecutionStatus.SUCCESS.name(), execTime); if (bDebug) { Debug.addRoutingDebug("Filter {" + filterName + " TYPE:" + filter.filterType() + " ORDER:" + filter.filterOrder() + "} Execution time = " + execTime + "ms"); Debug.compareContextState(filterName, copy); } break; default: break; } if (t != null) throw t; usageNotifier.notify(filter, s); return o; } catch (Throwable e) { if (bDebug) { Debug.addRoutingDebug("Running Filter failed " + filterName + " type:" + filter.filterType() + " order:" + filter.filterOrder() + " " + e.getMessage()); } usageNotifier.notify(filter, ExecutionStatus.FAILED); if (e instanceof ZuulException) { throw (ZuulException) e; } else { ZuulException ex = new ZuulException(e, "Filter threw Exception", 500, filter.filterType() + ":" + filterName); ctx.addFilterExecutionSummary(filterName, ExecutionStatus.FAILED.name(), execTime); throw ex; } } } /** * Publishes a counter metric for each filter on each use. */ public static class BasicFilterUsageNotifier implements FilterUsageNotifier { private static final String METRIC_PREFIX = "zuul.filter-"; @Override public void notify(ZuulFilter filter, ExecutionStatus status) { DynamicCounter.increment(METRIC_PREFIX + filter.getClass().getSimpleName(), "status", status.name(), "filtertype", filter.filterType()); } }}通过上面的代码中，可以看到得到简单的流程图
在官方示例中，提供了两个简单的 Route 的 ZuulFilter 实现
SimpleHostRoutingFilter.groovy
在这个示例中，在 Filter 实现中将请求复制并转发到目标服务，这个是简单的逻辑
class SimpleHostRoutingFilter extends ZuulFilter { // 声明这个过滤器是 route 类型 @Override String filterType() { return 'route' } // 过滤器的执行逻辑 Object run() { HttpServletRequest request = RequestContext.getCurrentContext().getRequest(); Header[] headers = buildZuulRequestHeaders(request) String verb = getVerb(request); InputStream requestEntity = request.getInputStream(); CloseableHttpClient httpclient = CLIENT.get() String uri = request.getRequestURI() if (RequestContext.getCurrentContext().requestURI != null) { uri = RequestContext.getCurrentContext().requestURI } try { // 将请求转发到指定服务器 HttpResponse response = forward(httpclient, verb, uri, request, headers, requestEntity) setResponse(response) } catch (Exception e) { throw e; } return null } HttpResponse forward(CloseableHttpClient httpclient, String verb, String uri, HttpServletRequest request, Header[] headers, InputStream requestEntity) { requestEntity = debug(verb, uri, request, headers, requestEntity) HttpHost httpHost = getHttpHost() HttpRequest httpRequest; switch (verb) { case 'POST': httpRequest = new HttpPost(uri + getQueryString()) InputStreamEntity entity = new InputStreamEntity(requestEntity, request.getContentLength()) httpRequest.setEntity(entity) break case 'PUT': httpRequest = new HttpPut(uri + getQueryString()) InputStreamEntity entity = new InputStreamEntity(requestEntity, request.getContentLength()) httpRequest.setEntity(entity) break; default: httpRequest = new BasicHttpRequest(verb, uri + getQueryString()) } try { httpRequest.setHeaders(headers) return forwardRequest(httpclient, httpHost, httpRequest) } finally { //httpclient.close(); } } HttpResponse forwardRequest(HttpClient httpclient, HttpHost httpHost, HttpRequest httpRequest) { return httpclient.execute(httpHost, httpRequest); }}ZuulNFRequest 结合 Netflix 的 route 过滤器
这个示例中，从 HttpClient 转发改为了使用 RibbonCommand 转发，从而使用了 Ribbon 的功能。关于 Ribbon 以后有时间再说
class ZuulNFRequest extends ZuulFilter { @Override String filterType() { return 'route' } boolean shouldFilter() { return NFRequestContext.currentContext.getRouteHost() == null && RequestContext.currentContext.sendZuulResponse() } Object run() { NFRequestContext context = NFRequestContext.currentContext HttpServletRequest request = context.getRequest(); MultivaluedMap<String, String> headers = buildZuulRequestHeaders(request) MultivaluedMap<String, String> params = buildZuulRequestQueryParams(request) Verb verb = getVerb(request); Object requestEntity = getRequestBody(request) IClient restClient = ClientFactory.getNamedClient(context.getRouteVIP()); String uri = request.getRequestURI() if (context.requestURI != null) { uri = context.requestURI } //remove double slashes uri = uri.replace("//", "/") HttpResponse response = forward(restClient, verb, uri, headers, params, requestEntity) setResponse(response) return response } def HttpResponse forward(RestClient restClient, Verb verb, uri, MultivaluedMap<String, String> headers, MultivaluedMap<String, String> params, InputStream requestEntity) { debug(restClient, verb, uri, headers, params, requestEntity)// restClient.apacheHttpClient.params.setVirtualHost(headers.getFirst("host")) String route = NFRequestContext.getCurrentContext().route if (route == null) { String path = RequestContext.currentContext.requestURI if (path == null) { path = RequestContext.currentContext.getRequest() getRequestURI() } route = "route" //todo get better name } route = route.replace("/", "_") RibbonCommand<AbstractLoadBalancerAwareClient<HttpRequest, HttpResponse>> command = new RibbonCommand<>(restClient, verb, uri, headers, params, requestEntity); try { HttpResponse response = command.execute(); return response } catch (HystrixRuntimeException e) { if (e?.fallbackException?.cause instanceof ClientException) { ClientException ex = e.fallbackException.cause as ClientException throw new ZuulException(ex, "Forwarding error", 500, ex.getErrorType().toString()) } throw new ZuulException(e, "Forwarding error", 500, e.failureType.toString()) } }}总结
从 zuul 实现中看，还是基于 Servlet 的，并在过程中加入 前、中、后和异常处理链。因为基于 Servlet 其处理流程是阻塞的，性能会有所下降。
在 zuul 里面采用了 java 和 groovy 混合编程的方式，编程更加灵活。通过自定了一个 GroovyCompiler 来加载指定路径的 groovy 文件来实现在运行中动态添加 ZuulFilter 这种动态机制在一定程度上实现了热更新 ZuulFilter 功能，也是值得学习的。
参考
GitHub: https://github.com/Netflix/zuul
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zuul1.x是如何实现请求转发的文档写的再好，也不如源码写的好源码地址：GitHub:https://github.com/Netflix/zuulGitee:https://gitee.com/github_mirror_plus/zuul目录简介实现逻辑源码基于Servlet的请求转发ZuulServlet核心代码ZuulRunner核心代码RequestContext核心代码FilterP
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