what's @EnableZuulProxy 是什么 ?

秒速五厘米 2022-02-13 21:30 242阅读 0赞

/*
     * Copyright 2013-2017 the original author or authors.
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     *      http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */
    
    package org.springframework.cloud.netflix.zuul;
    
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
    import org.springframework.context.annotation.Import;
    
    /**
     * Sets up a Zuul server endpoint and installs some reverse proxy filters in it, so it can
     * forward requests to backend servers. The backends can be registered manually through
     * configuration or via DiscoveryClient.
     *
     * @see EnableZuulServer for how to get a Zuul server without any proxying
     *
     * @author Spencer Gibb
     * @author Dave Syer
     * @author Biju Kunjummen
     */
    @EnableCircuitBreaker
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Import(ZuulProxyMarkerConfiguration.class)
    public @interface EnableZuulProxy {
    }

可以看到, 它同时含有注解 @EnableCircuitBreaker

它的定义为:

package org.springframework.cloud.client.circuitbreaker;
    
    import java.lang.annotation.Documented;
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Inherited;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    import org.springframework.context.annotation.Import;
    
    /**
     * Annotation to enable a CircuitBreaker implementation.
     * http://martinfowler.com/bliki/CircuitBreaker.html
     * @author Spencer Gibb
     */
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Inherited
    @Import(EnableCircuitBreakerImportSelector.class)
    public @interface EnableCircuitBreaker {
    
    }

同时, 也会注意到, 它有一个引入Configuration的地方:  @Import(ZuulProxyMarkerConfiguration.class)

其详细内容为:

package org.springframework.cloud.netflix.zuul;
    
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.Configuration;
    
    /**
     * 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 {
    	}
    }

那么, 引发两个问题:

1- 什么Marker bean?

(vjia:  @Configuration注解, 就相当于一个 xml实行的 bean定义的xml文件; 也就是说, 这里定义一个@Configuration的ZuulProxyMarkerCOnfiguration纯粹是为了定义并注入一个 Marker类型的 bean)

注意看这里的注释:

> Responsible for adding in a marker bean to trigger activation of ZuulProxyAutoConfiguration

可以猜测, 类 ZuulProxyAutoConfiguration肯定有个@ConditionOnBean注解.

验证, 打开 类 ZuulProxyAutoConfiguration:

package org.springframework.cloud.netflix.zuul;
    
    import java.util.Collections;
    import java.util.List;
    
    import com.netflix.zuul.filters.FilterRegistry;
    import org.apache.http.impl.client.CloseableHttpClient;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.boot.actuate.condition.ConditionalOnEnabledEndpoint;
    import org.springframework.boot.actuate.endpoint.Endpoint;
    import org.springframework.boot.actuate.trace.TraceRepository;
    import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
    import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
    import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
    import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingClass;
    import org.springframework.cloud.client.actuator.HasFeatures;
    import org.springframework.cloud.client.discovery.DiscoveryClient;
    import org.springframework.cloud.client.discovery.event.HeartbeatEvent;
    import org.springframework.cloud.client.discovery.event.HeartbeatMonitor;
    import org.springframework.cloud.client.discovery.event.InstanceRegisteredEvent;
    import org.springframework.cloud.client.discovery.event.ParentHeartbeatEvent;
    import org.springframework.cloud.client.serviceregistry.Registration;
    import org.springframework.cloud.commons.httpclient.ApacheHttpClientConnectionManagerFactory;
    import org.springframework.cloud.commons.httpclient.ApacheHttpClientFactory;
    import org.springframework.cloud.commons.httpclient.HttpClientConfiguration;
    import org.springframework.cloud.netflix.ribbon.support.RibbonRequestCustomizer;
    import org.springframework.cloud.netflix.zuul.filters.ProxyRequestHelper;
    import org.springframework.cloud.netflix.zuul.filters.RouteLocator;
    import org.springframework.cloud.netflix.zuul.filters.TraceProxyRequestHelper;
    import org.springframework.cloud.netflix.zuul.filters.ZuulProperties;
    import org.springframework.cloud.netflix.zuul.filters.discovery.DiscoveryClientRouteLocator;
    import org.springframework.cloud.netflix.zuul.filters.discovery.ServiceRouteMapper;
    import org.springframework.cloud.netflix.zuul.filters.discovery.SimpleServiceRouteMapper;
    import org.springframework.cloud.netflix.zuul.filters.pre.PreDecorationFilter;
    import org.springframework.cloud.netflix.zuul.filters.route.RibbonCommandFactory;
    import org.springframework.cloud.netflix.zuul.filters.route.RibbonRoutingFilter;
    import org.springframework.cloud.netflix.zuul.filters.route.SimpleHostRoutingFilter;
    import org.springframework.cloud.netflix.zuul.web.ZuulHandlerMapping;
    import org.springframework.context.ApplicationEvent;
    import org.springframework.context.ApplicationListener;
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.Configuration;
    import org.springframework.context.annotation.Import;
    
    /**
     * @author Spencer Gibb
     * @author Dave Syer
     * @author Biju Kunjummen
     */
    @Configuration
    @Import({ RibbonCommandFactoryConfiguration.RestClientRibbonConfiguration.class,
    		RibbonCommandFactoryConfiguration.OkHttpRibbonConfiguration.class,
    		RibbonCommandFactoryConfiguration.HttpClientRibbonConfiguration.class,
    		HttpClientConfiguration.class })
    @ConditionalOnBean(ZuulProxyMarkerConfiguration.Marker.class)
    public class ZuulProxyAutoConfiguration extends ZuulServerAutoConfiguration {
    
    	@SuppressWarnings("rawtypes")
    	@Autowired(required = false)
    	private List<RibbonRequestCustomizer> requestCustomizers = Collections.emptyList();
    
    	@Autowired(required = false)
    	private Registration registration;
    
    	@Autowired
    	private DiscoveryClient discovery;
    
    	@Autowired
    	private ServiceRouteMapper serviceRouteMapper;
    
    	@Override
    	public HasFeatures zuulFeature() {
    		return HasFeatures.namedFeature("Zuul (Discovery)",
    				ZuulProxyAutoConfiguration.class);
    	}
    
    	@Bean
    	@ConditionalOnMissingBean(DiscoveryClientRouteLocator.class)
    	public DiscoveryClientRouteLocator discoveryRouteLocator() {
    		return new DiscoveryClientRouteLocator(this.server.getServletPrefix(),
    				this.discovery, this.zuulProperties, this.serviceRouteMapper, this.registration);
    	}
    
    	// 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;
    	}
    
    	@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);
    	}
    
    	@Bean
    	public ApplicationListener<ApplicationEvent> zuulDiscoveryRefreshRoutesListener() {
    		return new ZuulDiscoveryRefreshListener();
    	}
    
    	@Bean
    	@ConditionalOnMissingBean(ServiceRouteMapper.class)
    	public ServiceRouteMapper serviceRouteMapper() {
    		return new SimpleServiceRouteMapper();
    	}
    
    	@Configuration
    	@ConditionalOnMissingClass("org.springframework.boot.actuate.endpoint.Endpoint")
    	protected static class NoActuatorConfiguration {
    
    		@Bean
    		public ProxyRequestHelper proxyRequestHelper(ZuulProperties zuulProperties) {
    			ProxyRequestHelper helper = new ProxyRequestHelper();
    			helper.setIgnoredHeaders(zuulProperties.getIgnoredHeaders());
    			helper.setTraceRequestBody(zuulProperties.isTraceRequestBody());
    			return helper;
    		}
    
    	}
    
    	@Configuration
    	@ConditionalOnClass(Endpoint.class)
    	protected static class EndpointConfiguration {
    
    		@Autowired(required = false)
    		private TraceRepository traces;
    
    		@ConditionalOnEnabledEndpoint("routes")
    		@Bean
    		public RoutesEndpoint routesEndpoint(RouteLocator routeLocator) {
    			return new RoutesEndpoint(routeLocator);
    		}
    
    		@ConditionalOnEnabledEndpoint("routes")
    		@Bean
    		public RoutesMvcEndpoint routesMvcEndpoint(RouteLocator routeLocator,
    				RoutesEndpoint endpoint) {
    			return new RoutesMvcEndpoint(endpoint, routeLocator);
    		}
    
    		@ConditionalOnEnabledEndpoint("filters")
    		@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;
    		}
    	}
    
    	private static class ZuulDiscoveryRefreshListener
    			implements ApplicationListener<ApplicationEvent> {
    
    		private HeartbeatMonitor monitor = new HeartbeatMonitor();
    
    		@Autowired
    		private ZuulHandlerMapping zuulHandlerMapping;
    
    		@Override
    		public void onApplicationEvent(ApplicationEvent event) {
    			if (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.monitor.update(value)) {
    				reset();
    			}
    		}
    
    		private void reset() {
    			this.zuulHandlerMapping.setDirty(true);
    		}
    
    	}
    
    }

\--TBC--