Eureka启动，原生启动与SpringCloudEureka启动异同
我们先看看作为原生的EurekaServer启动的过程，作为一个Servlet应用，他的启动入口就是他的主要ServletContextListener类（这里是EurekaBootStrap）的contextInitialized方法
EurekaServerBootstrap
@Override
public void contextInitialized(ServletContextEvent event) {
try {
initEurekaEnvironment();
initEurekaServerContext();
ServletContext sc = event.getServletContext();
sc.setAttribute(EurekaServerContext.class.getName(), serverContext);
} catch (Throwable e) {
logger.error("Cannot bootstrap eureka server :", e);
throw new RuntimeException("Cannot bootstrap eureka server :", e);
}
}
可以看出主要做了两件事，initEurekaEnvironment()与initEurekaServerContext()
对于initEurekaEnvironment()只是初始化一些必要的环境变量，由于Eureka配置基于Spring的配置中间件Archaius，这些环境变量都是针对这个配置中间件使用的。
initEurekaServerContext()是我们重点需要关心的，它初始化了EurekaServer需要的所有组件：
protected void initEurekaServerContext() throws Exception {
EurekaServerConfig eurekaServerConfig = new DefaultEurekaServerConfig();
//设置json与xml序列化工具
JsonXStream.getInstance().registerConverter(new V1AwareInstanceInfoConverter(), XStream.PRIORITY_VERY_HIGH);
XmlXStream.getInstance().registerConverter(new V1AwareInstanceInfoConverter(), XStream.PRIORITY_VERY_HIGH);
logger.info("Initializing the eureka client...");
logger.info(eurekaServerConfig.getJsonCodecName());
ServerCodecs serverCodecs = new DefaultServerCodecs(eurekaServerConfig);
ApplicationInfoManager applicationInfoManager = null;
//初始化EurekaClient，EurekaClient用来与其他EurekaServer进行交互
//有可能通过guice初始化Eureka，这时eurekaClient和ApplicationInfoManager通过依赖注入先被初始化
if (eurekaClient == null) {
EurekaInstanceConfig instanceConfig = isCloud(ConfigurationManager.getDeploymentContext())
? new CloudInstanceConfig()
: new MyDataCenterInstanceConfig();
applicationInfoManager = new ApplicationInfoManager(
instanceConfig, new EurekaConfigBasedInstanceInfoProvider(instanceConfig).get());
EurekaClientConfig eurekaClientConfig = new DefaultEurekaClientConfig();
eurekaClient = new DiscoveryClient(applicationInfoManager, eurekaClientConfig);
} else {
applicationInfoManager = eurekaClient.getApplicationInfoManager();
}
//初始化PeerAwareInstanceRegistry, 这个类里面的方法就是与集群内其他EurekaServer实例保持业务同步的机制
PeerAwareInstanceRegistry registry;
if (isAws(applicationInfoManager.getInfo())) {
registry = new AwsInstanceRegistry(
eurekaServerConfig,
eurekaClient.getEurekaClientConfig(),
serverCodecs,
eurekaClient
);
awsBinder = new AwsBinderDelegate(eurekaServerConfig, eurekaClient.getEurekaClientConfig(), registry, applicationInfoManager);
awsBinder.start();
} else {
registry = new PeerAwareInstanceRegistryImpl(
eurekaServerConfig,
eurekaClient.getEurekaClientConfig(),
serverCodecs,
eurekaClient
);
}
//初始化PeerEurekaNodes，里面有定时维护Eureka集群的业务逻辑
PeerEurekaNodes peerEurekaNodes = getPeerEurekaNodes(
registry,
eurekaServerConfig,
eurekaClient.getEurekaClientConfig(),
serverCodecs,
applicationInfoManager
);
//初始化EurekaServer上下文
serverContext = new DefaultEurekaServerContext(
eurekaServerConfig,
serverCodecs,
registry,
peerEurekaNodes,
applicationInfoManager
);
EurekaServerContextHolder.initialize(serverContext);
serverContext.initialize();
logger.info("Initialized server context");
//从其他节点中读取注册信息，并开放服务注册
// Copy registry from neighboring eureka node
int registryCount = registry.syncUp();
registry.openForTraffic(applicationInfoManager, registryCount);
// Register all monitoring statistics.
EurekaMonitors.registerAllStats();
}
总结下来，总共如下几点：
1.初始化并设置序列化反序列化工具
2.初始化通信客户端EurekaClient
3.初始化集群通信类PeerAwareInstanceRegistry与PeerEurekaNodes
4.初始化EurekaServer上下文serverContext
5.从其他节点中读取注册信息，并开放服务注册
然后，由于原生的EurekaServer利用Jersey框架初始化restApi，这里还有：
6.载入Jersey，初始化Restful服务api
对于胶水代码，实现了大致同样的但是略微有些区别的功能：
一、 Server 有哪些功能:
提供服务注册功能。
消费者可以获取服务列表。
服务可以续约。
Server 集群之间的数据共享
二、 提供服务注册功能
我们使用 EurekaServer 的时候，需要在启动类上加入 @EnableEurekaServer注解，这个注解肯定就是我们研究的入口。
EnableEurekaServer 类：
/**
- Annotation to activate Eureka Server related configuration.
- {@link EurekaServerAutoConfiguration}
- @author Dave Syer
- @author Biju Kunjummen
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(EurekaServerMarkerConfiguration.class)
public @interface EnableEurekaServer {
}
EurekaServerAutoConfiguration
@Configuration
@Import(EurekaServerInitializerConfiguration.class)
@ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class)
@EnableConfigurationProperties({ EurekaDashboardProperties.class,
InstanceRegistryProperties.class })
@PropertySource("classpath:/eureka/server.properties")
public class EurekaServerAutoConfiguration extends WebMvcConfigurerAdapter{
...
}
EurekaServerInitializerConfiguration 由于实现了SmartLifecycle, 初始化启动start()方法； 额外新创建一个线程初始化initEurekaServerContext() , 发布事件等工作
@Configuration
public class EurekaServerInitializerConfiguration
implements ServletContextAware, SmartLifecycle, Ordered {
@Override
public void start() {
new Thread(new Runnable() {
@Override
public void run() {
try {
// TODO: is this class even needed now?
eurekaServerBootstrap.contextInitialized(
EurekaServerInitializerConfiguration.this.servletContext);
log.info("Started Eureka Server");
publish(new EurekaRegistryAvailableEvent(getEurekaServerConfig()));
EurekaServerInitializerConfiguration.this.running = true;
publish(new EurekaServerStartedEvent(getEurekaServerConfig()));
}
catch (Exception ex) {
// Help!
log.error("Could not initialize Eureka servlet context", ex);
}
}
}).start();
}
}
EurekaServerAutoConfiguration 中注入EurekaServerContext
@Bean
public EurekaServerContext eurekaServerContext(ServerCodecs serverCodecs,
PeerAwareInstanceRegistry registry, PeerEurekaNodes peerEurekaNodes) {
return new DefaultEurekaServerContext(this.eurekaServerConfig, serverCodecs,
registry, peerEurekaNodes, this.applicationInfoManager);
}
在初始化化DefaultEurekaServerContext 类的时候，会初始化initialize（）方法，是因为在此方法上面@PostConstruct注解. peerEurekaNodes.start() 中。使用单定时任务线程池，维护eureka节点
@PostConstruct
@Override
public void initialize() {
logger.info("Initializing ...");
peerEurekaNodes.start();
try {
registry.init(peerEurekaNodes);
} catch (Exception e) {
throw new RuntimeException(e);
}
logger.info("Initialized");
}