SpringCloud之zuul源碼解析

                                              Zuul源碼解析    

    zuul各版本實現存在一些微小的變化，總的實現思想未改變，以spring-cloud-netflix-core-1.3.6.RELEASE爲例

     1、zuul的重要的初始化類

    org.springframework.cloud.netflix.zuul.ZuulServerAutoConfiguration

    org.springframework.cloud.netflix.zuul.ZuulProxyAutoConfiguration

     org.springframework.cloud.netflix.zuul.ZuulFilterInitializer

     org.springframework.cloud.netflix.zuul.RibbonCommandFactoryConfiguration

      ZuulServerAutoConfiguration

      初始化路由規則

      初始化一些重要的filter如 PreDecorationFilter，RibbonRoutingFilter

      初始化ZuulFilterInitializer

      初始化ZuulHandlerMapping

      代碼以下

//路由規則
    @Bean
	@ConditionalOnMissingBean(DiscoveryClientRouteLocator.class)
	public DiscoveryClientRouteLocator discoveryRouteLocator() {
		return new DiscoveryClientRouteLocator(this.server.getServletPrefix(), this.discovery, this.zuulProperties,
				this.serviceRouteMapper);
	}
     
	// pre filters
	@Bean
	public PreDecorationFilter preDecorationFilter(RouteLocator routeLocator, ProxyRequestHelper proxyRequestHelper) {
		return new PreDecorationFilter(routeLocator, this.server.getServletPrefix(), this.zuulProperties,
				proxyRequestHelper);
	}

	// route filters
	@Bean
	public RibbonRoutingFilter ribbonRoutingFilter(ProxyRequestHelper helper,
			RibbonCommandFactory<?> ribbonCommandFactory) {
		RibbonRoutingFilter filter = new RibbonRoutingFilter(helper, ribbonCommandFactory, this.requestCustomizers);
		return filter;
	}

  	@Configuration
	protected static class ZuulFilterConfiguration {

		@Autowired
		private Map<String, ZuulFilter> filters;

		@Bean
		public ZuulFilterInitializer zuulFilterInitializer(
				CounterFactory counterFactory, TracerFactory tracerFactory) {
			FilterLoader filterLoader = FilterLoader.getInstance();
			FilterRegistry filterRegistry = FilterRegistry.instance();
			return new ZuulFilterInitializer(this.filters, counterFactory, tracerFactory, filterLoader, filterRegistry);
		}

	}
	@Bean
	public ZuulController zuulController() {
		return new ZuulController();
	}

	@Bean
	public ZuulHandlerMapping zuulHandlerMapping(RouteLocator routes) {
		ZuulHandlerMapping mapping = new ZuulHandlerMapping(routes, zuulController());
		mapping.setErrorController(this.errorController);
		return mapping;
	}

ZuulProxyAutoConfiguration

 zuulProxAutoConfiguration繼承ZuulServerAutoConfiguration功能上和zuulServerAutoConfiguration

主要功能是增長了RibbonCommandFactoryConfiguration的配置，初始化全部的實現ribbon的方式如apache,okhttp。

 ZuulFilterInitializer

   該類的做用主要是把初始化的過濾器註冊到zuul的FilterRegistry，FilterRegistry是一個單例用於初始化路由信息，在ZuulRunner中使用

RibbonCommandFactoryConfiguration

  主要做用是配置轉發的實現，實現主要有apache，okhttp

2、zuul的轉發實現

   首先第一步轉到ZuulHandlerMapping中的lookupHandler方法，把轉發轉到zuulController中

@Override
	protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception {
		if (this.errorController != null && urlPath.equals(this.errorController.getErrorPath())) {
			return null;
		}
		String[] ignored = this.routeLocator.getIgnoredPaths().toArray(new String[0]);
		if (PatternMatchUtils.simpleMatch(ignored, urlPath)) {
			return null;
		}
		RequestContext ctx = RequestContext.getCurrentContext();
		if (ctx.containsKey("forward.to")) {
			return null;
		}
		if (this.dirty) {
			synchronized (this) {
				if (this.dirty) {
					registerHandlers();
					this.dirty = false;
				}
			}
		}
		return super.lookupHandler(urlPath, request);
	}

  第一次訪問時dirty爲true會初始化一次請求規則以下

private void registerHandlers() {
		Collection<Route> routes = this.routeLocator.getRoutes();
		if (routes.isEmpty()) {
			this.logger.warn("No routes found from RouteLocator");
		}
		else {
			for (Route route : routes) {
				registerHandler(route.getFullPath(), this.zuul);
			}
		}
	}

第二步ZuulController繼承ServletWrappingController的會把請求轉到ZuulServlet中以下

/**
 * @author Spencer Gibb
 */
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();
		}
	}

}

第三步ZuulServlet的service方法以下主要執行pre,route,postRoute三種路由器

@Override
    public void service(javax.servlet.ServletRequest servletRequest, javax.servlet.ServletResponse servletResponse) throws ServletException, IOException {
        try {
            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
            RequestContext context = RequestContext.getCurrentContext();
            context.setZuulEngineRan();

            try {
                preRoute();
            } catch (ZuulException e) {
                error(e);
                postRoute();
                return;
            }
            try {
                route();
            } catch (ZuulException e) {
                error(e);
                postRoute();
                return;
            }
            try {
                postRoute();
            } catch (ZuulException e) {
                error(e);
                return;
            }

        } catch (Throwable e) {
            error(new ZuulException(e, 500, "UNHANDLED_EXCEPTION_" + e.getClass().getName()));
        } finally {
            RequestContext.getCurrentContext().unset();
        }
    }

4、最後由SendResponseFilter執行返回結果,filterOrder爲1000因此最好post的filter不要超過1000不然影響返回結果