zuul 作为springCloud 的全家桶组件之一，有着不可或缺的分量。它作为一个普通java API网关，自有网关的好处：
避免将内部信息暴露给外部；
统一服务端应用入口；
为微服务添加额外的安全层；
支持混合通信协议；
降低构建微服务的复杂性；
微服务模拟与虚拟化；
zuul 基本上已经被springCloud 处理为一个开箱即用的一个组件了，所以基本上只需要添加相应依赖和一些必要配置，该网关就可以跑起来了。（这表面和nginx反向代理部分功能看起来是差不多的）
让我们来快速实践一下吧！
一、zuul入坑基本实践步骤
1.1. 引入 pom 依赖
<parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.0.5.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent> <modelVersion>4.0.0</modelVersion> <groupId>zuul-test</groupId> <artifactId>com.youge</artifactId> <version>1.0</version> <!-- 引入spingcloud 全家桶 --> <dependencyManagement> <dependencies> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-dependencies</artifactId> <version>Finchley.RC2</version> <type>pom</type> <scope>import</scope> </dependency> </dependencies> </dependencyManagement> <dependencies> <!-- 导入服务网关zuul --> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-netflix-zuul</artifactId> </dependency> </dependencies>
以上就是我们整个demo的全部maven依赖了，很简洁吧。这也是springboot的初衷，把所有的工作都移到幕后，让业务更简洁。
1.2. 编写网关入口类
如下为整个网关的入口类，实际上就是两个注解发生了化学反应。@EnableZuulProxy 是本文的主角，它会开启网关相关的服务。
@SpringBootApplication @EnableZuulProxy public class MyZuulGateway { // 只有一个空的main方法 public static void main(String[] args) { SpringApplication.run(MyZuulGateway.class, args); } }
就是这么简单！
1.3. 添加测试配置项
在application.properties配置文件中添加如下配置，主要使用一个路由配置验证即可！
server.port=9000 spring.application.name=my-zuul-gateway #本地环境配置zuul转发的规则： # 忽略所有微服务，只路由指定微服务 # 如下配置为将 /sapi/** 的路径请求，转发到 http://127.0.0.1:8082/fileenc/ 上去。 zuul.ignored-services=* zuul.routes.fileenc1.url=http://127.0.0.1:8082/fileenc/ zuul.routes.fileenc1.path=/sapi/**
如上就可以将网关跑起来了，如果你连后台服务也没有，没关系，自己写一个就好了。
@GetMapping("hello")
public Object hello() {
return "hello, world";
}
1.4. 测试网关
以上就已经将整个网关搞好了，run一下就ok. 测试方式就是直接浏览器里访问下该网关地址就好了:
http://localhost:9000/sapi/test/hello?a=1&b=22 .
如果你看到 “hello, world”, 恭喜你，zuul已入坑。
二、zuul是如何转发请求的？
根据上面的观察，zuul已经基本可以满足我们的开发需求了，后续更多要做的可能就是一些安全相关，业务相关，优化相关的东西了。不过在做这些之前，我们可以先多问一个问题，zuul是如何将请求转发给后台服务的呢？
这实际上和zuul的架构相关：
zuul的中核心概念是：Filter. 运行时逻辑上分为多种类型的Filter，各类型Filter处理时机不同！ PRE：这种过滤器在请求被路由之前调用；ROUTING：这种过滤器将请求路由到微服务；POST：这种过滤器在路由到微服务以后执行；ERROR：在其他阶段发生错误时执行该过滤器；
所以，整体上来说，它的转发流程会经过一系列的过滤器，然后再进行实际的转发。
如果只想了解其最终是如何转的可以直奔主题，而如果要添加你的功能，则需要编写一些对应生命周期的过滤器。
原本要分析zuul是如何处理请求的，但是实际上，zuul被整合到spring之后，就完全地符合了一个springmvc的编程模型了。所有对该网关的请求会先调用 ZuulController 进行请求的接收，然后到 service处理，再到响应这么一个过程。
整个 ZuulController 非常地简单：就是一个请求的委托过程！
// org.springframework.cloud.netflix.zuul.web.ZuulController public class ZuulController extends ServletWrappingController { public ZuulController() { setServletClass(ZuulServlet.class); setServletName("zuul"); setSupportedMethods((String[]) null); // Allow all } @Override public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception { try { // We don't care about the other features of the base class, just want to // handle the request return super.handleRequestInternal(request, response); } finally { // @see com.netflix.zuul.context.ContextLifecycleFilter.doFilter RequestContext.getCurrentContext().unset(); } } } // org.springframework.web.servlet.mvc.ServletWrappingController#handleRequestInternal /** * Invoke the wrapped Servlet instance. * @see javax.servlet.Servlet#service(javax.servlet.ServletRequest, javax.servlet.ServletResponse) */ @Override protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response) throws Exception { Assert.state(this.servletInstance != null, "No Servlet instance"); // 该 servletInstance 是 ZuulServlet, 整个zuul的实现框架由其控制 this.servletInstance.service(request, response); return null; } // com.netflix.zuul.http.ZuulServlet#service @Override public void service(javax.servlet.ServletRequest servletRequest, javax.servlet.ServletResponse servletResponse) throws ServletException, IOException { try { // 初始化请求，由 zuulRunner 处理 init((HttpServletRequest) servletRequest, (HttpServletResponse) servletResponse); // Marks this request as having passed through the "Zuul engine", as opposed to servlets // explicitly bound in web.xml, for which requests will not have the same data attached // setZuulEngineRan 会旋转一个标识： "zuulEngineRan", true RequestContext context = RequestContext.getCurrentContext(); context.setZuulEngineRan(); try { // 前置过滤器 preRoute(); } catch (ZuulException e) { error(e); // 异常时直接调用后置路由完成请求 postRoute(); return; } try { // 正常的路由请求处理 route(); } catch (ZuulException e) { error(e); postRoute(); return; } try { // 正常地后置路由处理 postRoute(); } catch (ZuulException e) { error(e); return; } } catch (Throwable e) { error(new ZuulException(e, 500, "UNHANDLED_EXCEPTION_" + e.getClass().getName())); } finally { // 重置上下文，以备下次使用 RequestContext.getCurrentContext().unset(); } }
以上就是整个zuul对于普通请求的处理框架部分了。逻辑还是比较清晰的，简单的，前置+转发+后置处理。我们就几个重点部分说明一下：
2.1. 请求初始化
该部分主要是将外部请求，接入到 zuul 的处理流程上，当然下面的实现主要是使用了 ThreadLocal 实现了上下文的衔接。
// com.netflix.zuul.http.ZuulServlet#init /** * initializes request * * @param servletRequest * @param servletResponse */ void init(HttpServletRequest servletRequest, HttpServletResponse servletResponse) { zuulRunner.init(servletRequest, servletResponse); } // com.netflix.zuul.ZuulRunner#init /** * sets HttpServlet request and HttpResponse * * @param servletRequest * @param servletResponse */ public void init(HttpServletRequest servletRequest, HttpServletResponse servletResponse) { // RequestContext 使用 ThreadLocal 进行保存，且保证有值 // 且 RequestContext 继承了 ConcurrentHashMap, 保证了操作的线程安全 RequestContext ctx = RequestContext.getCurrentContext(); if (bufferRequests) { ctx.setRequest(new HttpServletRequestWrapper(servletRequest)); } else { ctx.setRequest(servletRequest); } ctx.setResponse(new HttpServletResponseWrapper(servletResponse)); }
以上就是一个 zuul 请求的初始化了，简单地说就是设置好请求上下文，备用。
2.2. 前置处理过滤器
前置处理过滤器主要用于标记一些请求类型，权限验证，安全过滤等等。是不可或缺一环。具体实现自行处理！我们来看一个整体的通用流程：
// com.netflix.zuul.http.ZuulServlet#preRoute /** * executes "pre" filters * * @throws ZuulException */ void preRoute() throws ZuulException { zuulRunner.preRoute(); } // com.netflix.zuul.ZuulRunner#preRoute /** * executes "pre" filterType ZuulFilters * * @throws ZuulException */ public void preRoute() throws ZuulException { // FilterProcessor 是个单例 FilterProcessor.getInstance().preRoute(); } // com.netflix.zuul.FilterProcessor#preRoute /** * runs all "pre" filters. These filters are run before routing to the orgin. * * @throws ZuulException */ public void preRoute() throws ZuulException { try { // 调用Type 为 pre 的过滤器 runFilters("pre"); } catch (ZuulException e) { throw e; } catch (Throwable e) { throw new ZuulException(e, 500, "UNCAUGHT_EXCEPTION_IN_PRE_FILTER_" + e.getClass().getName()); } } // com.netflix.zuul.FilterProcessor#runFilters /** * 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; // 通过 FilterLoader 的单例，获取所有注册为 sType 的过滤器 // 存放 Filters 的容器自然也是线程安全的，为 ConcurrentHashMap // - org.springframework.cloud.netflix.zuul.filters.pre.ServletDetectionFilter // - org.springframework.cloud.netflix.zuul.filters.pre.Servlet30WrapperFilter // - org.springframework.cloud.netflix.zuul.filters.pre.FormBodyWrapperFilter // - org.springframework.cloud.netflix.zuul.filters.pre.DebugFilter // - org.springframework.cloud.netflix.zuul.filters.pre.PreDecorationFilter List<ZuulFilter> list = FilterLoader.getInstance().getFiltersByType(sType); if (list != null) { for (int i = 0; i < list.size(); i++) { ZuulFilter zuulFilter = list.get(i); // 依次处理每个 filter Object result = processZuulFilter(zuulFilter); if (result != null && result instanceof Boolean) { bResult |= ((Boolean) result); } } } return bResult; } // 获取相应的 filters // com.netflix.zuul.FilterLoader#getFiltersByType /** * Returns a list of filters by the filterType specified * * @param filterType * @return a List<ZuulFilter> */ public List<ZuulFilter> getFiltersByType(String filterType) { List<ZuulFilter> list = hashFiltersByType.get(filterType); if (list != null) return list; list = new ArrayList<ZuulFilter>(); Collection<ZuulFilter> filters = filterRegistry.getAllFilters(); for (Iterator<ZuulFilter> iterator = filters.iterator(); iterator.hasNext(); ) { ZuulFilter filter = iterator.next(); if (filter.filterType().equals(filterType)) { list.add(filter); } } Collections.sort(list); // sort by priority hashFiltersByType.putIfAbsent(filterType, list); return list; } // com.netflix.zuul.FilterProcessor#processZuulFilter /** * 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(); } // 调用各filter的 runFilter() 方法，触发filter作用 // 如果filter被禁用，则不会调用 zuul.ServletDetectionFilter.pre.disable=true, 代表禁用 pre // 具体实现逻辑由各 filter 决定 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(); // 使用 StringBuilder 记录请求处理日志 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; } // 只要发生异常，则抛出 if (t != null) throw t; // 请求计数器增加 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; } } } // com.netflix.zuul.ZuulFilter#runFilter /** * runFilter checks !isFilterDisabled() and shouldFilter(). The run() method is invoked if both are true. * * @return the return from ZuulFilterResult */ public ZuulFilterResult runFilter() { ZuulFilterResult zr = new ZuulFilterResult(); // 如果被禁用则不会触发真正地调用 if (!isFilterDisabled()) { // shouldFilter() 由各filter决定，返回true时执行filter if (shouldFilter()) { Tracer t = TracerFactory.instance().startMicroTracer("ZUUL::" + this.getClass().getSimpleName()); try { Object res = run(); zr = new ZuulFilterResult(res, ExecutionStatus.SUCCESS); } catch (Throwable e) { t.setName("ZUUL::" + this.getClass().getSimpleName() + " failed"); zr = new ZuulFilterResult(ExecutionStatus.FAILED); zr.setException(e); } finally { t.stopAndLog(); } } else { // 打上跳过标识 zr = new ZuulFilterResult(ExecutionStatus.SKIPPED); } } return zr; } // run样例： org.springframework.cloud.netflix.zuul.filters.pre.ServletDetectionFilter#run @Override public Object run() { RequestContext ctx = RequestContext.getCurrentContext(); HttpServletRequest request = ctx.getRequest(); if (!(request instanceof HttpServletRequestWrapper) && isDispatcherServletRequest(request)) { ctx.set(IS_DISPATCHER_SERVLET_REQUEST_KEY, true); } else { ctx.set(IS_DISPATCHER_SERVLET_REQUEST_KEY, false); } return null; }
如上，就是一个preFilter的处理流程了：
1. 从 FilterLoader 中获取所有 pre 类型的filter;
2. 依次调用各filter的runFilter()方法，触发filter;
3. 调用前先调用 shouldFilter() 进行判断该filter对于此次请求是否有用, 各filter实现可以从上下文中取得相应的信息，各自判定;
4. 计数器加1;
5. 默认就会有多个filter可调用, 不够满足业务场景再自行添加，各业务执行方法为 run();
2.3. 正常路由处理
zuul 的本职工作，是对路径的转发路由（正向代理 or 反向代理），如下处理：
// com.netflix.zuul.http.ZuulServlet#route /** * executes "route" filters * * @throws ZuulException */ void route() throws ZuulException { zuulRunner.route(); } // com.netflix.zuul.ZuulRunner#route /** * executes "route" filterType ZuulFilters * * @throws ZuulException */ public void route() throws ZuulException { FilterProcessor.getInstance().route(); } // com.netflix.zuul.FilterProcessor#route /** * Runs all "route" filters. These filters route calls to an origin. * * @throws ZuulException if an exception occurs. */ public void route() throws ZuulException { try { // 同样，获取filter类型为 route 的 filters, 进行调用处理即可 // - org.springframework.cloud.netflix.zuul.filters.route.RibbonRoutingFilter // - org.springframework.cloud.netflix.zuul.filters.route.SimpleHostRoutingFilter // - org.springframework.cloud.netflix.zuul.filters.route.SendForwardFilter runFilters("route"); } catch (ZuulException e) { throw e; } catch (Throwable e) { throw new ZuulException(e, 500, "UNCAUGHT_EXCEPTION_IN_ROUTE_FILTER_" + e.getClass().getName()); } } // 其中，Ribbon 的处理需要有 ribbon 组件的引入和配置 // org.springframework.cloud.netflix.zuul.filters.route.RibbonRoutingFilter#shouldFilter @Override public boolean shouldFilter() { RequestContext ctx = RequestContext.getCurrentContext(); // 判断是否有 serviceId, 且 sendZuulResponse=true 才会进行 ribbon 处理 return (ctx.getRouteHost() == null && ctx.get(SERVICE_ID_KEY) != null && ctx.sendZuulResponse()); } 以下是普通路由转发的实现,只要配置了相应的路由信息，则会进行相关转发： // org.springframework.cloud.netflix.zuul.filters.route.SimpleHostRoutingFilter#shouldFilter @Override public boolean shouldFilter() { return RequestContext.getCurrentContext().getRouteHost() != null && RequestContext.getCurrentContext().sendZuulResponse(); } @Override public Object run() { RequestContext context = RequestContext.getCurrentContext(); // step1. 构建http请求头信息 HttpServletRequest request = context.getRequest(); MultiValueMap<String, String> headers = this.helper .buildZuulRequestHeaders(request); // step2. 构建 params 信息, 如: a=111&&b=222 MultiValueMap<String, String> params = this.helper .buildZuulRequestQueryParams(request); // 获取请求类型, GET,POST,PUT,DELETE String verb = getVerb(request); // step3. 构建请求体信息，如文件 InputStream requestEntity = getRequestBody(request); // 如果没有 Content-Length 字段，则设置 chunkedRequestBody:true if (getContentLength(request) < 0) { context.setChunkedRequestBody(); } // step4. 构建要转发的uri地址信息 String uri = this.helper.buildZuulRequestURI(request); this.helper.addIgnoredHeaders(); try { // step5. 请求转发出去，等待响应 // 具体如何转发请求，是在 forward 中处理的 CloseableHttpResponse response = forward(this.httpClient, verb, uri, request, headers, params, requestEntity); // 将结果放到上下文中，以备后续filter处理 setResponse(response); } catch (Exception ex) { throw new ZuulRuntimeException(ex); } return null; } // step1. 构建http请求头信息 // org.springframework.cloud.netflix.zuul.filters.ProxyRequestHelper#buildZuulRequestHeaders public MultiValueMap<String, String> buildZuulRequestHeaders( HttpServletRequest request) { RequestContext context = RequestContext.getCurrentContext(); MultiValueMap<String, String> headers = new HttpHeaders(); Enumeration<String> headerNames = request.getHeaderNames(); // 获取所有的 header 信息，还原到 headers 中 if (headerNames != null) { while (headerNames.hasMoreElements()) { String name = headerNames.nextElement(); // 排除一些特别的的头信息 if (isIncludedHeader(name)) { Enumeration<String> values = request.getHeaders(name); while (values.hasMoreElements()) { String value = values.nextElement(); headers.add(name, value); } } } } // 添加本次路由转发新增的头信息 Map<String, String> zuulRequestHeaders = context.getZuulRequestHeaders(); for (String header : zuulRequestHeaders.keySet()) { headers.set(header, zuulRequestHeaders.get(header)); } headers.set(HttpHeaders.ACCEPT_ENCODING, "gzip"); return headers; } // step2. 构建 params 信息, 如: a=111&&b=222 // org.springframework.cloud.netflix.zuul.filters.ProxyRequestHelper#buildZuulRequestQueryParams public MultiValueMap<String, String> buildZuulRequestQueryParams( HttpServletRequest request) { // 解析 getQueryString 中的 a=111&b=222... 信息 Map<String, List<String>> map = HTTPRequestUtils.getInstance().getQueryParams(); MultiValueMap<String, String> params = new LinkedMultiValueMap<>(); if (map == null) { return params; } for (String key : map.keySet()) { for (String value : map.get(key)) { params.add(key, value); } } return params; } // 解析请求url中的k=v&k2=v2 为 map 格式 // com.netflix.zuul.util.HTTPRequestUtils#getQueryParams /** * returns query params as a Map with String keys and Lists of Strings as values * @return */ public Map<String, List<String>> getQueryParams() { Map<String, List<String>> qp = RequestContext.getCurrentContext().getRequestQueryParams(); if (qp != null) return qp; HttpServletRequest request = RequestContext.getCurrentContext().getRequest(); qp = new LinkedHashMap<String, List<String>>(); if (request.getQueryString() == null) return null; StringTokenizer st = new StringTokenizer(request.getQueryString(), "&"); int i; while (st.hasMoreTokens()) { String s = st.nextToken(); i = s.indexOf("="); if (i > 0 && s.length() >= i + 1) { String name = s.substring(0, i); String value = s.substring(i + 1); try { name = URLDecoder.decode(name, "UTF-8"); } catch (Exception e) { } try { value = URLDecoder.decode(value, "UTF-8"); } catch (Exception e) { } List<String> valueList = qp.get(name); if (valueList == null) { valueList = new LinkedList<String>(); qp.put(name, valueList); } valueList.add(value); } else if (i == -1) { String name=s; String value=""; try { name = URLDecoder.decode(name, "UTF-8"); } catch (Exception e) { } List<String> valueList = qp.get(name); if (valueList == null) { valueList = new LinkedList<String>(); qp.put(name, valueList); } valueList.add(value); } } RequestContext.getCurrentContext().setRequestQueryParams(qp); return qp; } // step3. 构建请求体信息，如文件 // org.springframework.cloud.netflix.zuul.filters.route.SimpleHostRoutingFilter#getRequestBody protected InputStream getRequestBody(HttpServletRequest request) { InputStream requestEntity = null; try { // 先向 requestEntity 中获取输入流，如果没有则向 servlet 中获取 requestEntity = (InputStream) RequestContext.getCurrentContext().get(REQUEST_ENTITY_KEY); if (requestEntity == null) { // 向 HttpServletRequest 中获取原始的输入流 requestEntity = request.getInputStream(); } } catch (IOException ex) { log.error("error during getRequestBody", ex); } return requestEntity; } // step4. 构建要转发的uri地址信息 // org.springframework.cloud.netflix.zuul.filters.ProxyRequestHelper#buildZuulRequestURI public String buildZuulRequestURI(HttpServletRequest request) { RequestContext context = RequestContext.getCurrentContext(); // 原始请求 uri String uri = request.getRequestURI(); // 路由转换之后的请求 uri String contextURI = (String) context.get(REQUEST_URI_KEY); if (contextURI != null) { try { // 防止乱码，urlencode 一下 uri = UriUtils.encodePath(contextURI, characterEncoding(request)); } catch (Exception e) { log.debug( "unable to encode uri path from context, falling back to uri from request", e); } } return uri; } // step5. 请求转发出去，等待响应 // 具体如何转发请求，是在 forward 中处理的 // org.springframework.cloud.netflix.zuul.filters.route.SimpleHostRoutingFilter#forward private CloseableHttpResponse forward(CloseableHttpClient httpclient, String verb, String uri, HttpServletRequest request, MultiValueMap<String, String> headers, MultiValueMap<String, String> params, InputStream requestEntity) throws Exception { Map<String, Object> info = this.helper.debug(verb, uri, headers, params, requestEntity); // 配置的路由地址前缀 URL host = RequestContext.getCurrentContext().getRouteHost(); HttpHost httpHost = getHttpHost(host); // 取出uri uri = StringUtils.cleanPath((host.getPath() + uri).replaceAll("/{2,}", "/")); long contentLength = getContentLength(request); ContentType contentType = null; if (request.getContentType() != null) { contentType = ContentType.parse(request.getContentType()); } // 使用InputStreamEntity封装inputStream请求，该inputStream是从socket接入后的原始输入流 // 后续 httpclient 进行数据读取时，将由其进行提供相应读数据方法 InputStreamEntity entity = new InputStreamEntity(requestEntity, contentLength, contentType); // 构建本次要请求的数据，关键 HttpRequest httpRequest = buildHttpRequest(verb, uri, entity, headers, params, request); try { log.debug(httpHost.getHostName() + " " + httpHost.getPort() + " " + httpHost.getSchemeName()); // 提交给 httpclient 组件执行 http 请求，并返回结果 CloseableHttpResponse zuulResponse = forwardRequest(httpclient, httpHost, httpRequest); this.helper.appendDebug(info, zuulResponse.getStatusLine().getStatusCode(), revertHeaders(zuulResponse.getAllHeaders())); return zuulResponse; } finally { // When HttpClient instance is no longer needed, // shut down the connection manager to ensure // immediate deallocation of all system resources // httpclient.getConnectionManager().shutdown(); } } // org.springframework.cloud.netflix.zuul.filters.route.SimpleHostRoutingFilter#buildHttpRequest protected HttpRequest buildHttpRequest(String verb, String uri, InputStreamEntity entity, MultiValueMap<String, String> headers, MultiValueMap<String, String> params, HttpServletRequest request) { HttpRequest httpRequest; String uriWithQueryString = uri + (this.forceOriginalQueryStringEncoding ? getEncodedQueryString(request) : this.helper.getQueryString(params)); // 根据原始请求的不同类型，做相应类型的转发 // 以下请求处理，都包含了对 文件流一类请求的逻辑 switch (verb.toUpperCase()) { case "POST": HttpPost httpPost = new HttpPost(uriWithQueryString); httpRequest = httpPost; httpPost.setEntity(entity); break; case "PUT": HttpPut httpPut = new HttpPut(uriWithQueryString); httpRequest = httpPut; httpPut.setEntity(entity); break; case "PATCH": HttpPatch httpPatch = new HttpPatch(uriWithQueryString); httpRequest = httpPatch; httpPatch.setEntity(entity); break; case "DELETE": BasicHttpEntityEnclosingRequest entityRequest = new BasicHttpEntityEnclosingRequest( verb, uriWithQueryString); httpRequest = entityRequest; // DELETE 时会做两步操作 entityRequest.setEntity(entity); break; default: // 除以上几种情况，都使用 BasicHttpRequest 进行处理即可 httpRequest = new BasicHttpRequest(verb, uriWithQueryString); log.debug(uriWithQueryString); } // 统一都设置请求头，将map转换为 BasicHeader httpRequest.setHeaders(convertHeaders(headers)); return httpRequest; } // org.springframework.cloud.netflix.zuul.filters.route.SimpleHostRoutingFilter#forwardRequest private CloseableHttpResponse forwardRequest(CloseableHttpClient httpclient, HttpHost httpHost, HttpRequest httpRequest) throws IOException { return httpclient.execute(httpHost, httpRequest); }
可见整个真正的转发流程，主要分几步：
1. 解析http请求头信息，并添加自己部分的头信息;
2. 解析并保留请求参数信息, 如: a=111&&b=222;
3. 获取原始的inputStream信息，如文件;
4. 根据路由配置，构建要转发的uri地址信息;
5. 使用httpclient组件，将请求转发出去，并等待响应，设置到 response中;
实际上，真正的转发仍然是依次做好相应判断，然后还原成对应的请求，再转发后后端服务中。
以上，就是一个普通的服务转发实现了。并没有太多的技巧，而是最基础的步骤：接收请求，解析参数，重新构建请求，请求后端，获得结果。
2.4. 后置过滤器
后置处理器可以做一些请求完服务端之后，对客户端的响应数据，包括正常数据流的输出，错误信息的返回等。如 SendResponseFilter, SendErrorFilter...
// com.netflix.zuul.http.ZuulServlet#postRoute /** * executes "post" ZuulFilters * * @throws ZuulException */ void postRoute() throws ZuulException { zuulRunner.postRoute(); } // com.netflix.zuul.ZuulRunner#postRoute /** * executes "post" filterType ZuulFilters * * @throws ZuulException */ public void postRoute() throws ZuulException { FilterProcessor.getInstance().postRoute(); } // com.netflix.zuul.FilterProcessor#postRoute /** * runs "post" filters which are called after "route" filters. ZuulExceptions from ZuulFilters are thrown. * Any other Throwables are caught and a ZuulException is thrown out with a 500 status code * * @throws ZuulException */ public void postRoute() throws ZuulException { try { // 获取类型为 post 的 filter, 调用 // 默认为: org.springframework.cloud.netflix.zuul.filters.post.SendResponseFilter runFilters("post"); } catch (ZuulException e) { throw e; } catch (Throwable e) { throw new ZuulException(e, 500, "UNCAUGHT_EXCEPTION_IN_POST_FILTER_" + e.getClass().getName()); } } // org.springframework.cloud.netflix.zuul.filters.post.SendResponseFilter#shouldFilter @Override public boolean shouldFilter() { // 有响应的数据，就可以进行处理 RequestContext context = RequestContext.getCurrentContext(); return context.getThrowable() == null && (!context.getZuulResponseHeaders().isEmpty() || context.getResponseDataStream() != null || context.getResponseBody() != null); } // org.springframework.cloud.netflix.zuul.filters.post.SendResponseFilter#run @Override public Object run() { try { // 添加header信息 addResponseHeaders(); // 输出数据流到请求端 writeResponse(); } catch (Exception ex) { ReflectionUtils.rethrowRuntimeException(ex); } return null; } // org.springframework.cloud.netflix.zuul.filters.post.SendResponseFilter#addResponseHeaders private void addResponseHeaders() { RequestContext context = RequestContext.getCurrentContext(); HttpServletResponse servletResponse = context.getResponse(); if (this.zuulProperties.isIncludeDebugHeader()) { @SuppressWarnings("unchecked") List<String> rd = (List<String>) context.get(ROUTING_DEBUG_KEY); if (rd != null) { StringBuilder debugHeader = new StringBuilder(); for (String it : rd) { debugHeader.append("[[[" + it + "]]]"); } servletResponse.addHeader(X_ZUUL_DEBUG_HEADER, debugHeader.toString()); } } // 向 response 中添加header List<Pair<String, String>> zuulResponseHeaders = context.getZuulResponseHeaders(); if (zuulResponseHeaders != null) { for (Pair<String, String> it : zuulResponseHeaders) { servletResponse.addHeader(it.first(), it.second()); } } if (includeContentLengthHeader(context)) { Long contentLength = context.getOriginContentLength(); if(useServlet31) { servletResponse.setContentLengthLong(contentLength); } else { //Try and set some kind of content length if we can safely convert the Long to an int if (isLongSafe(contentLength)) { servletResponse.setContentLength(contentLength.intValue()); } } } } // org.springframework.cloud.netflix.zuul.filters.post.SendResponseFilter#writeResponse() private void writeResponse() throws Exception { RequestContext context = RequestContext.getCurrentContext(); // there is no body to send if (context.getResponseBody() == null && context.getResponseDataStream() == null) { return; } HttpServletResponse servletResponse = context.getResponse(); if (servletResponse.getCharacterEncoding() == null) { // only set if not set servletResponse.setCharacterEncoding("UTF-8"); } OutputStream outStream = servletResponse.getOutputStream(); InputStream is = null; try { if (context.getResponseBody() != null) { String body = context.getResponseBody(); is = new ByteArrayInputStream( body.getBytes(servletResponse.getCharacterEncoding())); } else { is = context.getResponseDataStream(); if (is!=null && context.getResponseGZipped()) { // if origin response is gzipped, and client has not requested gzip, // decompress stream before sending to client // else, stream gzip directly to client if (isGzipRequested(context)) { servletResponse.setHeader(ZuulHeaders.CONTENT_ENCODING, "gzip"); } else { is = handleGzipStream(is); } } } if (is!=null) { writeResponse(is, outStream); } } finally { /** * We must ensure that the InputStream provided by our upstream pooling mechanism is ALWAYS closed * even in the case of wrapped streams, which are supplied by pooled sources such as Apache's * PoolingHttpClientConnectionManager. In that particular case, the underlying HTTP connection will * be returned back to the connection pool iif either close() is explicitly called, a read * error occurs, or the end of the underlying stream is reached. If, however a write error occurs, we will * end up leaking a connection from the pool without an explicit close() * * @author Johannes Edmeier */ if (is != null) { try { is.close(); } catch (Exception ex) { log.warn("Error while closing upstream input stream", ex); } } try { Object zuulResponse = context.get("zuulResponse"); if (zuulResponse instanceof Closeable) { ((Closeable) zuulResponse).close(); } outStream.flush(); // The container will close the stream for us } catch (IOException ex) { log.warn("Error while sending response to client: " + ex.getMessage()); } } } // org.springframework.cloud.netflix.zuul.filters.post.SendResponseFilter#writeResponse private void writeResponse(InputStream zin, OutputStream out) throws Exception { // 默认大小 8192 byte[] bytes = buffers.get(); int bytesRead = -1; // 依次向 outputStream 中写入字节流 while ((bytesRead = zin.read(bytes)) != -1) { out.write(bytes, 0, bytesRead); } }
同样，对客户端的输出，就是这么简单：解析出header信息，将response write() 到客户端的socket中。即完成任务。
以上，我们主要看了几个非常普通的filter的处理过程，理解了下 zuul 的运行流程，当然主要的目的分析zuul是如何转发请求的。基本上上面所有的filter都会继承 ZuulFilter 的抽象，它提供两个重要的统一的方法：isFilterDisabled() 和 shouldFilter() 方法用于控制过虑器是否启用或者是否应该使用，并统一了返回结果。
zuul 整体实现也是非常简单明了，基于模板方法模式 和 责任链模式 和 单例模式，基本搞定。只是更多的花需要应用自己去玩了。
三、自行实现一个业务filter
要想做到通用的框架，这点事情是必须要做的。当然，还必须要足够简单，如下：一个注解加一个继承实现即可！
// 一个注解，@Component, 成功 spring bean 组件 // 一个继承，ZuulFilter, 以使 zuul 框架可以按照规范进行filter 的接入 @Component public class MyOneFilter extends ZuulFilter { private final UrlPathHelper urlPathHelper = new UrlPathHelper(); @Autowired private ZuulProperties zuulProperties; @Autowired private RouteLocator routeLocator; public MyOneFilter() { } public MyOneFilter(ZuulProperties zuulProperties, RouteLocator routeLocator) { this.routeLocator = routeLocator; this.zuulProperties = zuulProperties; } @Override public String filterType() { // 自定义过滤器的类型，知道为什么不用枚举类吗？嘿嘿 return PRE_TYPE; } @Override public int filterOrder() { // 定义过滤器的出场顺序，越小越牛 return 1; } @Override public boolean shouldFilter() { // 是否可以启用当前filter, 按你的业务规则来说了算 return true; } @Override public Object run() { // 如果满足了过滤条件，你想怎么做都行，RequestContext中有你想要的一切 RequestContext ctx = RequestContext.getCurrentContext(); Route route = routeLocator.getMatchingRoute( urlPathHelper.getPathWithinApplication(ctx.getRequest())); System.out.println("in my one filter"); return null; } }
至于其他配置项什么的，自行查看官网即可！ https://www.springcloud.cc/spring-cloud-greenwich.html#_router_and_filter_zuul
四、几点思考
zuul 既然作为cloud的通用网关，必然会承受着比其他应用更大的流量，同时也要担起着比其他应用更高的QOC。可谓责任重大！
然而纵观前面的实现，并没有什么牛逼的技术。相反，看到更多是为了业务的需要，需要进行反复的数据拷贝。
很显然，网关类的服务，是非常典型的IO密集型应用，但似乎并没有看到它在这方面的努力(默认web服务器是tomcat，这就是其上限，如果换成netty又当如何)。也许，它还得需要前置网关，负载均衡，流量分发，才能够发挥其应有的作用。（把它当作普通应用就没事了，虽然它也在做负载均衡流量分发）
对于大文件的上传，它是通过先将文件流存储到本地临时文件，再上传后端服务中，这个过程必然会导致响应缓慢以及应对异常能力的变弱。 而且，普通网关请求 zuul 中对于会从servlet中获取输入流，并转化为byte数组，也就是说他会保持全量上传数据，这对于超大文件来说，肯定是不可取的。所以，官网上也特别说你得如何小心处理大文件的上传！