Spring Cloud之Eureka Server启动流程分析

待我称王封你为后i 2021-11-16 14:42 308阅读 0赞

## 启动流程分析图如下： ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3RocXR6cQ_size_16_color_FFFFFF_t_70]

1.  Eureka Server启动类：

/**
     1. 启动一个服务注册中心，只需要一个注解@EnableEurekaServer
     */
    @EnableEurekaServer
    @SpringBootApplication
    public class EurekaServerApplication {
        public static void main(String[] args) {
            SpringApplication.run(EurekaServerApplication.class, args);
        }
    }

1.  注解@EnableEurekaServer源码：我们看到该注解导入了EurekaServerMarkerConfiguration类

@Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Import(EurekaServerMarkerConfiguration.class)
    public @interface EnableEurekaServer {
    
    }

1.  EurekaServerMarkerConfiguration类作为配置文件，引入Marker类，激活 EurekaServerAutoConfiguration

/**
     *  激活 EurekaServerAutoConfiguration 的开关 
     * Responsible for adding in a marker bean to activate
     * {@link EurekaServerAutoConfiguration}.
     *
     * @author Biju Kunjummen
     */
    @Configuration
    public class EurekaServerMarkerConfiguration {
    
    	@Bean
    	public Marker eurekaServerMarkerBean() {
    		return new Marker();
    	}
    	class Marker {
    	}
    }

我们看到只是实例化了一个空类，没有任何实现，从注释中可以看到 EurekaServerMarkerConfiguration 是一个激活 EurekaServerAutoConfiguration 的开关。我们在项目源码的 META-INF/spring.factories中看到

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
      org.springframework.cloud.netflix.eureka.server.EurekaServerAutoConfiguration

进入EurekaServerMarkerConfiguration，点击idea左上角的圆标，即可看到：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3RocXR6cQ_size_16_color_FFFFFF_t_70 1]

1.  EurekaServerAutoConfiguration源码：  
    真正的配置信息在 EurekaServerAutoConfiguration 中，我们看到 @ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class) 只有存在 Marker 实例的时候，才会继续加载配置项，这也就要求必须有 @EnableEurekaServer 注解，才能正常的启动。

@Configuration
    @Import(EurekaServerInitializerConfiguration.class)
    @ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class)
    @EnableConfigurationProperties({ EurekaDashboardProperties.class,
    		InstanceRegistryProperties.class })
    @PropertySource("classpath:/eureka/server.properties")
    public class EurekaServerAutoConfiguration extends WebMvcConfigurerAdapter {
    
    }

在源码中我们可以看到一个很重要的注解 @Import(EurekaServerInitializerConfiguration.class) ，该注解是真正的的启动了服务

1、@Configuration 表明这是一个配置类
    2、@Import(EurekaServerInitializerConfiguration.class) 导入启动EurekaServer的bean
    3、@ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class) 这个是表示只有在spring容器
    里面含有Market这个实例的时候，才会加载当前这个Bean（EurekaServerAutoConfiguration ），这个就是控制
    是否开启EurekaServer的关键，
    
    4、@EnableConfigurationProperties({ EurekaDashboardProperties.class, InstanceRegistryProperties.class })
    加载配置
    5、@PropertySource(“classpath:/eureka/server.properties”) 加载配置文件。

1.  EurekaServerInitializerConfiguration源码核心代码如下：

@Configuration
    public class EurekaServerInitializerConfiguration
    		implements ServletContextAware, SmartLifecycle, Ordered {
    	@Autowired
    	private EurekaServerConfig eurekaServerConfig;
    
    	private ServletContext servletContext;
    
    	@Autowired
    	private ApplicationContext applicationContext;
    
    	@Autowired
    	private EurekaServerBootstrap eurekaServerBootstrap;
    
    	@Override
    	public void start() {
    		new Thread(new Runnable() {
    			@Override
    			public void run() {
    				try {
    					//1，初始化eurekaServer，同时启动eurekaServer
    					eurekaServerBootstrap.contextInitialized(
    							EurekaServerInitializerConfiguration.this.servletContext);
    					log.info("Started Eureka Server");
    					//2，发布Eureka注册事件
    					publish(new EurekaRegistryAvailableEvent(getEurekaServerConfig()));
    					//3，设置EurekaServer的状态为true
    					EurekaServerInitializerConfiguration.this.running = true;
    					//4，发布EurekaServer启动事件
    					publish(new EurekaServerStartedEvent(getEurekaServerConfig()));
    				}
    				catch (Exception ex) {
    					log.error("Could not initialize Eureka servlet context", ex);
    				}
    			}
    		}).start();
    	}
    }

该类继承了SmartLifecycle，重写了它的start()方法，开启一个线程做了一些初始化的工作。

1.  EurekaServerBootstrap类做的一些启动事件：

public void contextInitialized(ServletContext context) {
    		try {
    			//1，初始化Eureka执行环境
    			initEurekaEnvironment();
    			//2，初始化Eureka上下文
    			initEurekaServerContext();
    			context.setAttribute(EurekaServerContext.class.getName(), this.serverContext);
    		}
    		catch (Throwable e) {
    			log.error("Cannot bootstrap eureka server :", e);
    			throw new RuntimeException("Cannot bootstrap eureka server :", e);
    		}
    	}

1.  EurekaServerBootstrap -> contextInitialized() -> initEurekaEnvironment()，初始化Eureka环境

protected void initEurekaEnvironment() throws Exception {
    		log.info("Setting the eureka configuration..");
    		//1，设置数据中心，启动时获取的是null，所以设置为默认值
    		String dataCenter = ConfigurationManager.getConfigInstance()
    				.getString(EUREKA_DATACENTER);
    		if (dataCenter == null) {
    			log.info(
    					"Eureka data center value eureka.datacenter is not set, defaulting to default");
    			ConfigurationManager.getConfigInstance()
    					.setProperty(ARCHAIUS_DEPLOYMENT_DATACENTER, DEFAULT);
    		}
    		else {
    			ConfigurationManager.getConfigInstance()
    					.setProperty(ARCHAIUS_DEPLOYMENT_DATACENTER, dataCenter);
    		}
    		//2，设置环境值，启动时也是null，设置为默认值
    		String environment = ConfigurationManager.getConfigInstance()
    				.getString(EUREKA_ENVIRONMENT);
    		if (environment == null) {
    			ConfigurationManager.getConfigInstance()
    					.setProperty(ARCHAIUS_DEPLOYMENT_ENVIRONMENT, TEST);
    			log.info(
    					"Eureka environment value eureka.environment is not set, defaulting to test");
    		}
    		else {
    			ConfigurationManager.getConfigInstance()
    					.setProperty(ARCHAIUS_DEPLOYMENT_ENVIRONMENT, environment);
    		}
    	}

1.  EurekaServerBootstrap -> contextInitialized() -> initEurekaServerContext()，初始化Eureka上下文

protected void initEurekaServerContext() throws Exception {
    		// For backward compatibility
    		JsonXStream.getInstance().registerConverter(new V1AwareInstanceInfoConverter(),
    				XStream.PRIORITY_VERY_HIGH);
    		XmlXStream.getInstance().registerConverter(new V1AwareInstanceInfoConverter(),
    				XStream.PRIORITY_VERY_HIGH);
    
    		if (isAws(this.applicationInfoManager.getInfo())) {
    			this.awsBinder = new AwsBinderDelegate(this.eurekaServerConfig,
    					this.eurekaClientConfig, this.registry, this.applicationInfoManager);
    			this.awsBinder.start();
    		}
    
    		EurekaServerContextHolder.initialize(this.serverContext);
    		log.info("Initialized server context");
    		//1，从邻近的eureka结点复制注册表
    		int registryCount = this.registry.syncUp();
    		this.registry.openForTraffic(this.applicationInfoManager, registryCount);
    
    		// 2，注册所有监控统计信息
    		EurekaMonitors.registerAllStats();
    	}

## 总结： ##

至此，EurekaServer启动完毕, EurekaServerBootstrap是完全复制了原生EurekaBootstrap的代码， 因为原生的Eureka是在servlet应用，但是spring cloud的应用是运行在内嵌的Tomcat的WEB服务器里面的，所以就使用EurekaServerBootstrap来做替换，最终使Eureka能够在spring boot中使用。

参考博客：[https://blog.csdn.net/u010647035/article/details/83048894][https_blog.csdn.net_u010647035_article_details_83048894]

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3RocXR6cQ_size_16_color_FFFFFF_t_70 1]: /images/20211116/294b74bb9875475caaa893cec90a7410.png
[https_blog.csdn.net_u010647035_article_details_83048894]: https://blog.csdn.net/u010647035/article/details/83048894