springcloud -zuul(2-执行流程及源码)

官方图

1.Servlet

zuul.servletPath默认配置为/zuul,故请求为/zuul开头的会跳过dispatcherServlet直接进入ZuulServlet,该配置可以自定义配置,例如用于大文件上传

2.ZuulServlet中service方法

public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
            try {
                this.init((HttpServletRequest)servletRequest, (HttpServletResponse)servletResponse);
                RequestContext context = RequestContext.getCurrentContext();
                context.setZuulEngineRan();

                try {
                    //运行pre过滤器
                    this.preRoute();
                } catch (ZuulException var12) {
                    //有异常,执行errorFilter
                    this.error(var12);
                    //再执行postFilter
                    this.postRoute();
                    return;
                }

                try {
                    //运行rote过滤器
                    this.route();
                } catch (ZuulException var13) {
                    //有异常,执行errorFilter
                    this.error(var13);
                    //再执行postFilter
                    this.postRoute();
                    return;
                }

                try {
                    //运行post过滤器
                    this.postRoute();
                } catch (ZuulException var11) {
                    //有异常,执行errorFilter
                    this.error(var11);
                }
            } catch (Throwable var14) {
                this.error(new ZuulException(var14, 500, "UNHANDLED_EXCEPTION_" + var14.getClass().getName()));
            } finally {
                RequestContext.getCurrentContext().unset();
            }
        }

3.FilterProcessor

其运行交由FilterProcessor中的方法runFilters,根据service中的顺序,取不同的filter类型,执行其中的run方法

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 = (ZuulFilter)list.get(i);
                    Object result = this.processZuulFilter(zuulFilter);//见下面zuulFilter的runFilter()
                    if (result != null && result instanceof Boolean) {
                        bResult |= ((Boolean)result).booleanValue();
                    }
                }
            }

            return bResult;
        }

zuulFilter的runFilter方法，当filter的shouldFilter()返回true时才执行run()方法

public ZuulFilterResult runFilter() {
            ZuulFilterResult zr = new ZuulFilterResult();
            if (!this.isFilterDisabled()) {
                if (this.shouldFilter()) {
                    Tracer t = TracerFactory.instance().startMicroTracer("ZUUL::" + this.getClass().getSimpleName());

                    try {
                        Object res = this.run();
                        zr = new ZuulFilterResult(res, ExecutionStatus.SUCCESS);
                    } catch (Throwable var7) {
                        t.setName("ZUUL::" + this.getClass().getSimpleName() + " failed");
                        zr = new ZuulFilterResult(ExecutionStatus.FAILED);
                        zr.setException(var7);
                    } finally {
                        t.stopAndLog();
                    }
                } else {
                    zr = new ZuulFilterResult(ExecutionStatus.SKIPPED);
                }
            }

            return zr;
        }

4.获取过滤器FilterRegistry

其中的属性private final ConcurrentHashMap<String, ZuulFilter> filters = new ConcurrentHashMap();
保存所有的过滤器
例子中有12个(其中有两个为自定义的)：

[org.springframework.cloud.netflix.zuul.filters.route.SimpleHostRoutingFilter@3dc68586, 
        org.springframework.cloud.netflix.zuul.filters.pre.Servlet30WrapperFilter@4001d8c1, 
        org.springframework.cloud.netflix.zuul.filters.pre.ServletDetectionFilter@60dc1a4e, 
        org.springframework.cloud.netflix.zuul.filters.pre.PreDecorationFilter@7a2fce12, 
        com.example.springbootzuul.filters.AuthFilter@14fc9bd, 
        org.springframework.cloud.netflix.zuul.filters.pre.DebugFilter@74960e9d, 
        org.springframework.cloud.netflix.zuul.filters.post.SendResponseFilter@61037caf, 
        org.springframework.cloud.netflix.zuul.filters.pre.FormBodyWrapperFilter@3c88191b, 
        org.springframework.cloud.netflix.zuul.filters.post.SendErrorFilter@670342a2, 
        com.example.springbootzuul.filters.LoginPostFilter@7ed49a7f, 
        org.springframework.cloud.netflix.zuul.filters.route.RibbonRoutingFilter@357bc488, 
        org.springframework.cloud.netflix.zuul.filters.route.SendForwardFilter@d5e575c]

5.各个filter作用

pre过滤器:

org.springframework.cloud.netflix.zuul.filters.pre.ServletDetectionFilter:
该过滤器order值为-3，是pre阶段第一个过滤器，并且总是会运行。主要用途是判断该请求是被spring的DispatcherServlet处理还是被zuul的ZuulServlet处理，并且将判断结果设置到context中，后续处理中可以依照此结果进行个性化处理
org.springframework.cloud.netflix.zuul.filters.pre.Servlet30WrapperFilter:
该过滤器order值为-2，是pre阶段第二个过滤器，并且总是会运行。Zuul默认仅对servlet2.5兼容，该过滤器可以将request包装成3.0兼容的形式
org.springframework.cloud.netflix.zuul.filters.pre.FormBodyWrapperFilter:
该过滤器order值为-1，是pre阶段第三个过滤器，仅针对两类请求生效，第一种是Context-Type为application/x-www-form-urlencoded，第二种是由spring的DispatcherServlet处理的Context-Type为multipart/form-data的请求。该过滤器的主要目的是将上述两种请求包装成FormBodyRequestWrapper
org.springframework.cloud.netflix.zuul.filters.pre.DebugFilter:
该过滤器order值为1，是pre阶段第四个过滤器，仅在请求参数中出现debug=true（参数名称可设置）时执行。具体执行逻辑就是在context中设置debugRouting=true及debugRequest=true。在后续执行中可以通过这两个值来预埋一些debug信息，用于出现问题时提供排查所需的信息
org.springframework.cloud.netflix.zuul.filters.pre.PreDecorationFilter:
该过滤器order值为5，是pre阶段最后一个过滤器，仅在forward.to和serviceId都没有出现在context中的时候才执行。具体来说就是对请求做一些预处理，包括使用RouteLocator获取路由信息，在context中设置一些后续处理需要的信息，还有就是在请求头中添加一些代理信息，比如X-Forwarded-For
com.example.springbootzuul.filters.AuthFilter 自定义的。。

route:

org.springframework.cloud.netflix.zuul.filters.route.RibbonRoutingFilter:
该过滤器order值为10，是route阶段第一个过滤器，仅在context中存在serviceId的情况下运行。存在serviceId，就是说需要面向服务进行路由，服务的路由信息就是我们上面讲过的两种方式，配置文件（静态）及服务注册。具体就是创建RibbonCommandContext，然后交由ribbon和hystrix向下游服务进行请求
org.springframework.cloud.netflix.zuul.filters.route.SimpleHostRoutingFilter:
该过滤器order值为100，是route阶段第二个过滤器，仅在context中存在routeHost的情况下运行。存在routeHost，就是说我们配置了具体的http或者https url的请求信息。具体逻辑就是通过HttpClient直接向目标url发起请求，不再经过ribbon及hystrix，所以也就没有负载均衡以及熔断
org.springframework.cloud.netflix.zuul.filters.route.SendForwardFilter:
该过滤器order值为500，是route阶段第三个（最后一个）过滤器，仅在context中存在forward.to的情况下运行。存在forward.to，就是说我们配置了类似forward:/index的请求信息。具体就是通过RequestDispatcher进行forward

post:

com.example.springbootzuul.filters.LoginPostFilter 自定义的。。
org.springframework.cloud.netflix.zuul.filters.post.SendResponseFilter:
该过滤器order值为1000，是post阶段最后一个过滤器，仅在context中存在zuulResponseHeaders、responseDataStream、responseBody（三者是或的关系）的情况下运行，简单来说，就是在有响应数据的时候运行。我们以responseBody举例，来看下responseBody是什么时候被设置到context中的。还记得RibbonRoutingFilter吧，在他的run方法中会调用一个setResponse方法，responseBody就是在这个方法中被设置到context中

error:

org.springframework.cloud.netflix.zuul.filters.post.SendErrorFilter@670342a2,
该过滤器order值为0，是error阶段唯一一个过滤器，仅在context中存在throwable的情况下运行，也就是说有异常产生的情况下运行。将错误状态码、错误信息、异常对象设置到request中，然后forward到/error（默认，可配置）。之后我们可以自己定义一个/error端口对错误进行响应

6.关于路由处理

6.1 Zuul在自动配置加载时注入了2个RouteLocator

CompositeRouteLocator:是 @Primary的,它是组合多个RouteLocator的Locator
DiscoveryClientRouteLocator:存放至CompositeRouteLocator的属性routeLocators中,当调用RouteLocator时会调用CompositeRouteLocator中的
DiscoveryClientRouteLocator中的locateRoutes方法运行后就已经加载了配置文件中所有路由信息，以及注册中心中的服务路由信息，有的通过URL路由，有的通过serviceId路由

protected LinkedHashMap<String, ZuulRoute> locateRoutes() {
                //保存ZuulRoute的LinkedHashMap
                LinkedHashMap<String, ZuulRoute> routesMap = new LinkedHashMap<String, ZuulRoute>();
                //调用父类SimpleRouteLocator#locateRoutes()
                //加载ZuulProperties中的所有配置文件中的路由信息
                routesMap.putAll(super.locateRoutes());
                //如果服务发现客户端discovery存在
                if (this.discovery != null) {
                    //将routesMap已经存在的配置文件中的ZuulRoute放入staticServices<serviceId, ZuulRoute>
                    Map<String, ZuulRoute> staticServices = new LinkedHashMap<String, ZuulRoute>();
                    for (ZuulRoute route : routesMap.values()) {
                        String serviceId = route.getServiceId();
                        
                        //如果serviceId为null，以id作为serviceId，此情况适合 zuul.routes.xxxx=/xxxx/** 的情况
                        if (serviceId == null) {
                            serviceId = route.getId();
                        }
                        if (serviceId != null) {
                            staticServices.put(serviceId, route);
                        }
                    }
                    // Add routes for discovery services by default
                    List<String> services = this.discovery.getServices(); //到注册中心找到所有service
                    String[] ignored = this.properties.getIgnoredServices()
                            .toArray(new String[0]);
                    //遍历services
                    for (String serviceId : services) {
                        // Ignore specifically ignored services and those that were manually
                        // configured
                        String key = "/" + mapRouteToService(serviceId) + "/**";
                        //如果注册中心的serviceId在staticServices集合中，并且此路由没有配置URL
                        //那么，更新路由的location为serviceId
                        if (staticServices.containsKey(serviceId)
                                && staticServices.get(serviceId).getUrl() == null) {
                            // Explicitly configured with no URL, cannot be ignored
                            // all static routes are already in routesMap
                            // Update location using serviceId if location is null
                            ZuulRoute staticRoute = staticServices.get(serviceId);
                            if (!StringUtils.hasText(staticRoute.getLocation())) {
                                staticRoute.setLocation(serviceId);
                            }
                        }
                        //如果注册中心的serviceId不在忽略范围内，且routesMap中还没有包含，添加到routesMap
                        //(例子中的配置#忽略所有服务 ignoredServices: '*')
                        if (!PatternMatchUtils.simpleMatch(ignored, serviceId)
                                && !routesMap.containsKey(key)) {
                            // Not ignored
                            routesMap.put(key, new ZuulRoute(key, serviceId));
                        }
                    }
                }
                
                // 如果routesMap中有 /** 的默认路由配置
                if (routesMap.get(DEFAULT_ROUTE) != null) {
                    ZuulRoute defaultRoute = routesMap.get(DEFAULT_ROUTE);
                    // Move the defaultServiceId to the end
                    routesMap.remove(DEFAULT_ROUTE);
                    routesMap.put(DEFAULT_ROUTE, defaultRoute);
                }
                //将routesMap中的数据微调后，放到values<String, ZuulRoute>，返回
                LinkedHashMap<String, ZuulRoute> values = new LinkedHashMap<>();
                for (Entry<String, ZuulRoute> entry : routesMap.entrySet()) {
                    String path = entry.getKey();
                    // Prepend with slash if not already present.
                    if (!path.startsWith("/")) {
                        path = "/" + path;
                    }
                    if (StringUtils.hasText(this.properties.getPrefix())) {
                        path = this.properties.getPrefix() + path;
                        if (!path.startsWith("/")) {
                            path = "/" + path;
                        }
                    }
                    values.put(path, entry.getValue());
                }
                
                return values;
            }

6.2 路由前的预处理:PreDecorationFilter.run()

public Object run() {
                RequestContext ctx = RequestContext.getCurrentContext();
                final String requestURI = this.urlPathHelper.getPathWithinApplication(ctx.getRequest());
                Route route = this.routeLocator.getMatchingRoute(requestURI); //如下.找到匹配的路由
                // ==== 匹配到路由信息
                if (route != null) {
                    String location = route.getLocation();
                    if (location != null) {
                        /** //RequestContext设置 requestURI：路由的pattern路径
                        //RequestContext设置 proxy：路由id
                        //设置需要忽略的敏感头信息，要么用全局默认的，要么用路由自定义的
                        //设置重试信息
                        //如果location是 http/https开头的，RequestContext设置 routeHost：URL
                        //如果location是 forward:开头的，RequestContext设置 forward信息、routeHost：null
                        //其它 RequestContext设置 serviceId、routeHost：null、X-Zuul-ServiceId
                        //是否添加代理头信息 X-Forwarded-For
                        //是否添加Host头信息
                        */
                    }
                }
                // ==== 没有匹配到路由信息
                else {
                    /**............*/
                }
                return null;
            }

RouteLocator.getMatchingRoute(requestURI)

public Route getMatchingRoute(final String path) {
                    return getSimpleMatchingRoute(path);
                }
                
                protected Map<String, ZuulRoute> getRoutesMap() {
                    if (this.routes.get() == null) {
                        this.routes.set(locateRoutes());
                    }
                    return this.routes.get();
                }

                protected Route getSimpleMatchingRoute(final String path) {
                    //未初始化则初始化
                    getRoutesMap();
                    //获取准确的path:根据servlet的类型将path中的serveletPath截取掉
                    String adjustedPath = adjustPath(path);
                    //通过path匹配已初化的ZuulRoute
                    ZuulRoute route = getZuulRoute(adjustedPath);
                    //通过ZuulRoute 获取route
                    return getRoute(route, adjustedPath);
                }

在获取Zuulroute后通过getRoute获取到最后的Route

protected Route getRoute(ZuulRoute route, String path) {
                    if (route == null) {
                        return null;
                    }
                    String targetPath = path;
                    //配置的前缀prefix
                    String prefix = this.properties.getPrefix();
                    if(prefix.endsWith("/")) {
                        prefix = prefix.substring(0, prefix.length() - 1);
                    }
                    //访问path以前缀开头且配置截取前缀为true(不配置默认为true),截取前缀
                    if (path.startsWith(prefix + "/") && this.properties.isStripPrefix()) {
                        targetPath = path.substring(prefix.length());
                    }
                    //配置截取前缀为true(不配置默认为true)
                    if (route.isStripPrefix()) {
                        //路由path有通配符
                        int index = route.getPath().indexOf("*") - 1;
                        if (index > 0) {
                            //最后的targetPath即为各个服务里的路径
                            String routePrefix = route.getPath().substring(0, index);
                            targetPath = targetPath.replaceFirst(routePrefix, "");
                            prefix = prefix + routePrefix;
                        }
                    }
                    //标记是否默认支持重试(未配置默认false)
                    Boolean retryable = this.properties.getRetryable();
                    if (route.getRetryable() != null) {
                        retryable = route.getRetryable();
                    }
                    return new Route(route.getId(), targetPath, route.getLocation(), prefix,
                            retryable,
                            route.isCustomSensitiveHeaders() ? route.getSensitiveHeaders() : null, 
                            route.isStripPrefix());
                }

6.3 处理路由

RibbonRoutingFilter:使用Ribbon、Hystrix和可插入的http客户端发送请求

public Object run() {
                    RequestContext context = RequestContext.getCurrentContext();
                    this.helper.addIgnoredHeaders();
                    try {
                        RibbonCommandContext commandContext = buildCommandContext(context);
                        ClientHttpResponse response = forward(commandContext);
                        setResponse(response);
                        return response;
                    }
                    catch (ZuulException ex) {
                        throw new ZuulRuntimeException(ex);
                    }
                    catch (Exception ex) {
                        throw new ZuulRuntimeException(ex);
                    }
                }

SimpleHostRoutingFilter:简单路由，通过HttpClient向预定的URL发送请求

public Object run() {
                    RequestContext context = RequestContext.getCurrentContext();
                    HttpServletRequest request = context.getRequest();
                    MultiValueMap<String, String> headers = this.helper
                            .buildZuulRequestHeaders(request);
                    MultiValueMap<String, String> params = this.helper
                            .buildZuulRequestQueryParams(request);
                    String verb = getVerb(request);
                    InputStream requestEntity = getRequestBody(request);
                    if (request.getContentLength() < 0) {
                        context.setChunkedRequestBody();
                    }
                    String uri = this.helper.buildZuulRequestURI(request);
                    this.helper.addIgnoredHeaders();
                    try {
                        CloseableHttpResponse response = forward(this.httpClient, verb, uri, request,
                                headers, params, requestEntity);
                        setResponse(response);
                    }
                    catch (Exception ex) {
                        throw new ZuulRuntimeException(ex);
                    }
                    return null;
                }

SendForwardFilter:forward到本地URL

public Object run() {
                    try {
                        RequestContext ctx = RequestContext.getCurrentContext();
                        String path = (String) ctx.get(FORWARD_TO_KEY);
                        RequestDispatcher dispatcher = ctx.getRequest().getRequestDispatcher(path);
                        if (dispatcher != null) {
                            ctx.set(SEND_FORWARD_FILTER_RAN, true);
                            if (!ctx.getResponse().isCommitted()) {
                                dispatcher.forward(ctx.getRequest(), ctx.getResponse());
                                ctx.getResponse().flushBuffer();
                            }
                        }
                    }
                    catch (Exception ex) {
                        ReflectionUtils.rethrowRuntimeException(ex);
                    }
                    return null;
                }

7.其他重要组件

FilterRegistry:使用ConcurrentHashMap存储全部的filter
RequestContext:请求上下文对象,继承于ConcurrentHashMap<String, Object>,用于请求时的所有参数或其他信息,该对象放入线程中的,故在各个filter中都可获取到
//注意这里的ThreadLocal实例的initialValue()方法，当ThreadLocal的get()方法返回null的时候总是会调用initialValue()方法

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);
                    }
                }
            };
            public RequestContext() {
                super();
            }
            public static RequestContext getCurrentContext() {
                /**省略*/
                if (testContext != null) return testContext;
                //当ThreadLocal的get()方法返回null的时候总是会调用initialValue()方法，所以这里是"无则新建RequestContext"的逻辑
                RequestContext context = threadLocal.get();
                return context;
            }

 参考资料:

　　https://www.cnblogs.com/liangzs/p/8946740.html

　　https://www.jianshu.com/p/2cc9e2ba2256