@EnableEurekaServer注解
@EnableEurekaServer
1.1 在项目启动类上使用@EnableEurekaServer，可以将项目作为SpringCloud中的注册中心。那么这个注解做了哪些事呢？
1.2 点进去@EnableEurekaServer 这个注解，可以看到介绍时是这样的：
Annotation to activate Eureka Server related configuration {@link EurekaServerAutoConfiguration}（**Eureka服务器相关配置EurekaServerAutoConfiguration的注释）
可以将@EnableEurekaServer 这个注解看作是一个开关，开启时，会**相关配置，会作为注册中心。同时，他又引入了EurekaServerMarkerConfiguration类。
1.3 点进去EurekaServerMarkerConfiguration这个类，可以看到介绍是这样的：
Responsible for adding in a marker bean to activate {@link EurekaServerAutoConfiguration}。（负责添加一个标记来**配置类EurekaServerAutoConfiguration）
这个类中，向容器注入了一个类EurekaServerMarkerConfiguration.Marker，作用就是**配置类。源代码是这样的：
@Configuration
public class EurekaServerMarkerConfiguration {
@Bean
public Marker eurekaServerMarkerBean() {
return new Marker();
}
class Marker {
}
}
1.4 下面来看配置类EurekaServerAutoConfiguration。这个类上面有三个比较重要的注释：
@Configuration
@Import(EurekaServerInitializerConfiguration.class)
@ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class)
@EnableConfigurationProperties({ EurekaDashboardProperties.class,
InstanceRegistryProperties.class })
@Configuration注解表示这是一个配置类，通过@Bean注解声明一些注入到Spring IOC容器中的Bean。
@Import(EurekaServerInitializerConfiguration.class)注解表示它导入了EurekaServerInitializerConfiguration这个类。
@ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class)注解表示只要Spring容器中有EurekaServerMarkerConfiguration.Marker.class类的实例存在，那么就会将这个EurekaServerAutoConfiguration也注入到Spring容器中。
@EnableConfigurationProperties注解 将EurekaDashboardProperties和InstanceRegistryProperties对应的配置属性类注入容器中
查看EurekaServerAutoConfiguration的源代码，可以发现它向Spring容器中注入了一些bean。举几个例子：
这个bean中保存了这个实例的一些信息，名称为"Eureka Server"
@Bean
public HasFeatures eurekaServerFeature() {
return HasFeatures.namedFeature("Eureka Server",
EurekaServerAutoConfiguration.class);
}
//matchIfMissing属性表示缺少该property时是否可以加载。如果为true，没有该property也会正常加载；反之报错
//这个是仪表盘相关的Bean
@Bean
@ConditionalOnProperty(prefix = "eureka.dashboard", name = "enabled", matchIfMissing = true)
public EurekaController eurekaController() {
return new EurekaController(this.applicationInfoManager);
}
这两个实例来自com.netflix.eureka，将相应的处理逻辑交到com.netflix.eureka中，它们接手了真正的EurekaServer的启动逻
辑，SpringCloud 只是在容器中将这些Bean初始化。
//
@Bean
public EurekaServerContext eurekaServerContext(ServerCodecs serverCodecs,
PeerAwareInstanceRegistry registry, PeerEurekaNodes peerEurekaNodes) {
return new DefaultEurekaServerContext(this.eurekaServerConfig, serverCodecs,
registry, peerEurekaNodes, this.applicationInfoManager);
}
@Bean
public EurekaServerBootstrap eurekaServerBootstrap(PeerAwareInstanceRegistry registry,
EurekaServerContext serverContext) {
return new EurekaServerBootstrap(this.applicationInfoManager,
this.eurekaClientConfig, this.eurekaServerConfig, registry,
serverContext);
}
向容器中初始化一个Jersey 过滤器。
tips:使用FilterRegistrationBean向Spring中注册过滤器十分方便。
@Bean
public FilterRegistrationBean jerseyFilterRegistration(
javax.ws.rs.core.Application eurekaJerseyApp) {
FilterRegistrationBean bean = new FilterRegistrationBean();
bean.setFilter(new ServletContainer(eurekaJerseyApp));
bean.setOrder(Ordered.LOWEST_PRECEDENCE);
bean.setUrlPatterns(
Collections.singletonList(EurekaConstants.DEFAULT_PREFIX + "/*"));
return bean;
}
1.5 现在，在回过头来看一下配置类EurekaServerAutoConfiguration导入的EurekaServerInitializerConfiguration
这个类。
首先可以发现它使用了@Configuration注解。然后实现了ServletContextAware, SmartLifecycle, Ordered三个接口，实现了这些接口的方法。
@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();
}
private EurekaServerConfig getEurekaServerConfig() {
return this.eurekaServerConfig;
}
private void publish(ApplicationEvent event) {
this.applicationContext.publishEvent(event);
}
@Override
public void stop() {
this.running = false;
eurekaServerBootstrap.contextDestroyed(this.servletContext);
}
上面代码主要实现了start() 和 stop()方法。这两个方法的主要作用是初始化servlet相关上下文，在start的时候调用EurekaServerBootstrap.contextInitialized，在stop的时候调用eurekaServerBootstrap.contextDestroyed，都是借助eurekaServerBootstrap类来实现，而eurekaServerBootstrap里头部分调用了EurekaServerContext。再来看EurekaServerBootstrap中contextInitialized()方法的代码：
public void contextInitialized(ServletContext context) {
try {
initEurekaEnvironment();
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);
}
}
protected void initEurekaEnvironment() throws Exception {
log.info("Setting the eureka configuration..");
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);
}
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);
}
}
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");
// Copy registry from neighboring eureka node
int registryCount = this.registry.syncUp();
this.registry.openForTraffic(this.applicationInfoManager, registryCount);
// Register all monitoring statistics.
EurekaMonitors.registerAllStats();
}
主要是调用了initEurekaEnvironment()和initEurekaServerContext()方法，来初始化环境配置和初始化上下文。可以看到
initEurekaEnvironment()是设置了一些属性值，在initEurekaServerContext()方法中主要调用了 EurekaServerContextHolder.initialize(this.serverContext),this.registry.syncUp(),
this.registry.openForTraffic(this.applicationInfoManager, registryCount),这三个方法。EurekaServerContextHolder.initialize(this.serverContext),this.registry.syncUp()主要是给非IOC容器引用EurekaServerContext,registry.syncUp()从其他eureka server获取实例信息，然后注册到本server，然后复制到其他server节点上。registry.openForTraffic()标识自身server的状态为UP，表示可以开始接收请求。