Spring Cloud微服务网关Zuul的注解@EnableZuulProxy或@EnableZuulServer做了什么事情

忘是亡心i 2023-09-26 20:23 34阅读 0赞

# 一、Zuul的工作原理 #

Zuul 1.x的版本是由Servlet以及一系列的Filter组成的，各个组件之间协同合作完成功能，且易于扩展。参看官方的架构图我画了张图：

![format_png][]

**Zuul声明周期：**

> HTTP Request -> DispatcherServlet -> ZuulHandlerMapping -> ZuulController -> ZuulServlet -> ZuulRunner -> FilterProcessor -> ZuulFilter -> HTTP Response

1、`ZuulServlet`通过`RequestContext`上下文管理着Zuul众多的Filter组成的核心组件。

2、当有请求进入Zuul时，由`DispatcherServlet`进行分发交给`ZuulHandlerMapping`处理初始化得到路由定位器`RouteLocator`，为后续的请求分发做准备，同时也有基于事件从服务中心拉去服务列表(`ZuulRefreshListener`)。

3、`ZuulController`继承了`ServletWrappingController`重写了handleRequest方法将`ZuulServlet`引入声明周期，之后所有的请求都会经过`ZuulServlet`。

4、在第一次调用的时候会初始化`ZuulRunner`，后面就会按照过滤链的顺序执行。`ZuulRunner`会将请求和相应初始化为`RequestContext`，封装成`FilterProcessor`转化为调用`preRoute()`、`route()`、`postRoute()`、`error()`。所以在Zuul中获取请求都是通过`RequestContext.getCurrentContext()`先获取当前上下文，再通过上下文获取当前的请求。

# 二、@EnableZuulPoxy和@EnableZuulServer注解 #

@EnableCircuitBreaker
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Import(ZuulProxyMarkerConfiguration.class)
    public @interface EnableZuulProxy {
    }
    
    
    
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Import(ZuulServerMarkerConfiguration.class)
    public @interface EnableZuulServer {
    }
    复制代码

在网关的启动类上，添加注解`@EnableZuulPoxy`后就可以启动Zuul网关的功能。从上面的源码可以看到除了`@EnableCircuitBreaker`启动了熔断器外还引入了一个自动配置的类`ZuulProxyMarkerConfiguration`。

/**
     * Responsible for adding in a marker bean to trigger activation of 
     * {@link ZuulProxyAutoConfiguration}
     *
     * @author Biju Kunjummen
     */
    @Configuration
    public class ZuulProxyMarkerConfiguration {
    	@Bean
    	public Marker zuulProxyMarkerBean() {
    		return new Marker();
    	}
    	class Marker {
    	}
    }
    复制代码

`ZuulProxyMarkerConfiguration`的源码十分简单啊！看不出什么来，不过注释里面说了添加`Marker` bean是为了触发`ZuulProxyAutoConfiguration`。

@Configuration
    @Import({ RibbonCommandFactoryConfiguration.RestClientRibbonConfiguration.class,
    		RibbonCommandFactoryConfiguration.OkHttpRibbonConfiguration.class,
    		RibbonCommandFactoryConfiguration.HttpClientRibbonConfiguration.class,
    		HttpClientConfiguration.class })
    @ConditionalOnBean(ZuulProxyMarkerConfiguration.Marker.class)
    public class ZuulProxyAutoConfiguration extends ZuulServerAutoConfiguration {
    	@Autowired(required = false)
    	private List<RibbonRequestCustomizer> requestCustomizers = Collections.emptyList();
    	@Autowired(required = false)
    	private Registration registration;
    	@Autowired
    	private DiscoveryClient discovery;
    	@Autowired
    	private ServiceRouteMapper serviceRouteMapper;
    	...
    }
    复制代码

很明显了`@ConditionalOnBean(ZuulProxyMarkerConfiguration.Marker.class)`条件注入。在`ZuulProxyAutoConfiguration`里面注入了很多的Bean

## 2.1 ZuulProxyAutoConfiguration ##

`ZuulProxyAutoConfiguration`继承了`ZuulServerAutoConfiguration`，拥有其全部功能并新增一下功能：

*  引入HTTP客户端的配置：支持Apache HttpClient 和 OkHttp：通过`@import`注解引入配置，因为Zuul也是要发起HTTP请后网关后的服务，所以是需要HTTP客户端。

@Import({ RibbonCommandFactoryConfiguration.RestClientRibbonConfiguration.class,
    		RibbonCommandFactoryConfiguration.OkHttpRibbonConfiguration.class,
    		RibbonCommandFactoryConfiguration.HttpClientRibbonConfiguration.class,
    		HttpClientConfiguration.class })
    复制代码

*  初始化服务注册、发现监听器：在发生服务注册到注册中心时触发路由刷新，`DiscoveryClientRouteLocator`完成路由新刷新功能。

@Bean
    @ConditionalOnMissingBean(DiscoveryClientRouteLocator.class)
    public DiscoveryClientRouteLocator discoveryRouteLocator() {
    	return new DiscoveryClientRouteLocator(this.server.getServlet().getServletPrefix(), this.discovery, this.zuulProperties,
    			this.serviceRouteMapper, this.registration);
    }
    复制代码

*  初始化服务列表监听器
 *  初始化Zuul自定义Endpoint：

@Configuration
    @ConditionalOnClass(Health.class)
    protected static class EndpointConfiguration {
    	@Autowired(required = false)
    	private HttpTraceRepository traces;
    	@Bean
    	@ConditionalOnEnabledEndpoint
    	public RoutesEndpoint routesEndpoint(RouteLocator routeLocator) {
    		return new RoutesEndpoint(routeLocator);
    	}
    	@ConditionalOnEnabledEndpoint
    	@Bean
    	public FiltersEndpoint filtersEndpoint() {
    		FilterRegistry filterRegistry = FilterRegistry.instance();
    		return new FiltersEndpoint(filterRegistry);
    	}
    	@Bean
    	public ProxyRequestHelper proxyRequestHelper(ZuulProperties zuulProperties) {
    		TraceProxyRequestHelper helper = new TraceProxyRequestHelper();
    		if (this.traces != null) {
    			helper.setTraces(this.traces);
    		}
    		helper.setIgnoredHeaders(zuulProperties.getIgnoredHeaders());
    		helper.setTraceRequestBody(zuulProperties.isTraceRequestBody());
    		return helper;
    	}
    }
    复制代码

*  初始化一些内置的Filter（ZuulServerAutoConfiguration没有的Filter）：根据HttpClient或OkHttp制定负载均衡的过滤器。

// pre filters
    @Bean
    @ConditionalOnMissingBean(PreDecorationFilter.class)
    public PreDecorationFilter preDecorationFilter(RouteLocator routeLocator, ProxyRequestHelper proxyRequestHelpe
    	return new PreDecorationFilter(routeLocator, this.server.getServlet().getServletPrefix(), this.zuulPropert
    			proxyRequestHelper);
    }
    // route filters
    @Bean
    @ConditionalOnMissingBean(RibbonRoutingFilter.class)
    public RibbonRoutingFilter ribbonRoutingFilter(ProxyRequestHelper helper,
    		RibbonCommandFactory<?> ribbonCommandFactory) {
    	RibbonRoutingFilter filter = new RibbonRoutingFilter(helper, ribbonCommandFactory,
    			this.requestCustomizers);
    	return filter;
    }
    @Bean
    @ConditionalOnMissingBean({SimpleHostRoutingFilter.class, CloseableHttpClient.class})
    public SimpleHostRoutingFilter simpleHostRoutingFilter(ProxyRequestHelper helper,
    		ZuulProperties zuulProperties,
    		ApacheHttpClientConnectionManagerFactory connectionManagerFactory,
    		ApacheHttpClientFactory httpClientFactory) {
    	return new SimpleHostRoutingFilter(helper, zuulProperties,
    			connectionManagerFactory, httpClientFactory);
    }
    @Bean
    @ConditionalOnMissingBean({SimpleHostRoutingFilter.class})
    public SimpleHostRoutingFilter simpleHostRoutingFilter2(ProxyRequestHelper helper,
    													   ZuulProperties zuulProperties,
    													   CloseableHttpClient httpClient) {
    	return new SimpleHostRoutingFilter(helper, zuulProperties,
    			httpClient);
    }
    复制代码

## 2.2 ZuulServerAutoConfiguration ##

同时可以看到`ZuulProxyAutoConfiguration`是继承了`ZuulServerAutoConfiguration`。同样`@ConditionalOnBean(ZuulServerMarkerConfiguration.Marker.class)`条件注入。所以说`@EnableZuulProxy`会把`ZuulServerAutoConfiguration`和`ZuulServerAutoConfiguration`注入到Spring容器中。

很大一部分的组件实在`ZuulServerAutoConfiguration`中注入到Spring容器的：

@Configuration
    @EnableConfigurationProperties({ ZuulProperties.class })
    @ConditionalOnClass(ZuulServlet.class)
    @ConditionalOnBean(ZuulServerMarkerConfiguration.Marker.class)
    // Make sure to get the ServerProperties from the same place as a normal web app would
    // FIXME @Import(ServerPropertiesAutoConfiguration.class)
    public class ZuulServerAutoConfiguration {
    	...
    }
    复制代码

*  初始化配置加载器：读取配置文件中的配置

@Autowired
    protected ZuulProperties zuulProperties;
    复制代码

*  初始化路由加载器：这里的路由加载器都是加载本地配置文件中配置的路由信息。如果是想要自己实现路由加载器，例如像`DiscoveryClientRouteLocator`就是注册中心发生注册事件时，加载新的服务路由的加载器。如果是基于数据库存储做动态路由信息，也要自己实现一个路由加载器。

@Bean
    @Primary
    public CompositeRouteLocator primaryRouteLocator(
    		Collection<RouteLocator> routeLocators) {
        // 这里整合所有的路由加载器，像要刷新路由时，会遍历Spring容器内所有的路由加载器一个个去刷新。
    	return new CompositeRouteLocator(routeLocators);
    }
    @Bean
    @ConditionalOnMissingBean(SimpleRouteLocator.class)
    public SimpleRouteLocator simpleRouteLocator() {
        // 这是最基本的路由加载器，无论是DiscoveryClientRouteLocator还是自定义的都需要继承SimpleRouteLocator
        // 所有的路由信息最终都会加载出来，被SimpleRouteLocator管理着
    	return new SimpleRouteLocator(this.server.getServlet().getServletPrefix(),
    			this.zuulProperties);
    }
    复制代码

*  初始化路由映射器：它会根据请求路径，通过路由加载器匹配可以访问的服务

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

*  初始化路由刷新监听器：这个是很核心的配置，因为这里监听着各种会触发路由刷新的事件。

@Bean
    public ApplicationListener<ApplicationEvent> zuulRefreshRoutesListener() {
    	return new ZuulRefreshListener();
    }
    
    private static class ZuulRefreshListener
    		implements ApplicationListener<ApplicationEvent> {
    	@Autowired
    	private ZuulHandlerMapping zuulHandlerMapping;
    	private HeartbeatMonitor heartbeatMonitor = new HeartbeatMonitor();
    	@Override
    	public void onApplicationEvent(ApplicationEvent event) {
    		if (event instanceof ContextRefreshedEvent
    				|| event instanceof RefreshScopeRefreshedEvent
    				|| event instanceof RoutesRefreshedEvent
    				|| event instanceof InstanceRegisteredEvent) {
    			reset();
    		}
    		else if (event instanceof ParentHeartbeatEvent) {
    			ParentHeartbeatEvent e = (ParentHeartbeatEvent) event;
    			resetIfNeeded(e.getValue());
    		}
    		else if (event instanceof HeartbeatEvent) {
    			HeartbeatEvent e = (HeartbeatEvent) event;
    			resetIfNeeded(e.getValue());
    		}
    	}
    	private void resetIfNeeded(Object value) {
    		if (this.heartbeatMonitor.update(value)) {
    			reset();
    		}
    	}
    	private void reset() {
    		this.zuulHandlerMapping.setDirty(true);
    	}
    }
    复制代码

*  初始化ZuulServlet加载器

@Bean
    @ConditionalOnMissingBean(name = "zuulServlet")
    public ServletRegistrationBean zuulServlet() {
    	ServletRegistrationBean<ZuulServlet> servlet = new ServletRegistrationBean<>(new ZuulServlet(),
    			this.zuulProperties.getServletPattern());
    	// The whole point of exposing this servlet is to provide a route that doesn't
    	// buffer requests.
    	servlet.addInitParameter("buffer-requests", "false");
    	return servlet;
    }
    复制代码

*  初始化ZuulController

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

*  初始化Filter执行解析器

@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);
    	}
    }@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);
    	}
    }
    复制代码

*  初始化一些内置的Filter：基本的过滤器，也是经常会在很多Zuul过滤链组成图中经常看到。

@Bean
    public ServletDetectionFilter servletDetectionFilter() {
    	return new ServletDetectionFilter();
    }
    @Bean
    public FormBodyWrapperFilter formBodyWrapperFilter() {
    	return new FormBodyWrapperFilter();
    }
    @Bean
    public DebugFilter debugFilter() {
    	return new DebugFilter();
    }
    @Bean
    public Servlet30WrapperFilter servlet30WrapperFilter() {
    	return new Servlet30WrapperFilter();
    }
    // post filters
    @Bean
    public SendResponseFilter sendResponseFilter(ZuulProperties properties) {
    	return new SendResponseFilter(zuulProperties);
    }
    @Bean
    public SendErrorFilter sendErrorFilter() {
    	return new SendErrorFilter();
    }
    @Bean
    public SendForwardFilter sendForwardFilter() {
    	return new SendForwardFilter();
    }
    复制代码

*  初始化Metrix监控

@Configuration
    protected static class ZuulMetricsConfiguration {
    	@Bean
    	@ConditionalOnMissingBean(CounterFactory.class)
    	public CounterFactory counterFactory() {
    		return new EmptyCounterFactory();
    	}
    	@ConditionalOnMissingBean(TracerFactory.class)
    	@Bean
    	public TracerFactory tracerFactory() {
    		return new EmptyTracerFactory();
    	}
    }
    复制代码

# 三、总结 #

本文配了较多的源码，主要是`ZuulProxyAutoConfiguration`和`ZuulServerAutoConfiguration`这两个SpringBoot自动配置类，涵盖了很多Zuul的组件，花点时间去阅读、debug会让你很快去了解去很多的工作流程和原理。虽然Zuul在国内越来越少人用了，但是源码还是值得学习的。

[format_png]: https://img-blog.csdnimg.cn/img_convert/541abc42c5e4d5b7979b8c3d0df0e2c5.webp?x-oss-process=image/format,png