启用EurekaServer
@SpringBootApplication
@EnableEurekaServer
public class EurekaApplication {
public static void main(String[] args) {
SpringApplication.run(EurekaApplication.class, args);
}
}
@EnableEurekaServer 源码：
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(EurekaServerMarkerConfiguration.class)
public @interface EnableEurekaServer {
}
将配置类 EurekaServerMarkerConfiguration 加入spring 容器。
EurekaServerMarkerConfiguration 的源码
/**
*
* 激活 EurekaServerAutoConfiguration 的开关
*/
@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
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 {
}
简单的梳理一下 @EnableEurekaServer 的流程为：
EurekaServerAutoConfiguration 源码
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，下面我们就看一下它都有哪些操作
@Configuration
@Import(EurekaServerInitializerConfiguration.class)
@ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class)
@EnableConfigurationProperties({ EurekaDashboardProperties.class,
InstanceRegistryProperties.class })
@PropertySource("classpath:/eureka/server.properties")
public class EurekaServerAutoConfiguration extends WebMvcConfigurerAdapter {
}
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。
EurekaServerInitializerConfiguration 实现了SmartLifecycle.start方法，在spring 初始化的时候，会被调用
@Configuration
@CommonsLog
public class EurekaServerInitializerConfiguration
implements ServletContextAware, SmartLifecycle, Ordered {
@Autowired
private EurekaServerConfig eurekaServerConfig;
private ServletContext servletContext;
@Autowired
private ApplicationContext applicationContext;
@Autowired
private EurekaServerBootstrap eurekaServerBootstrap;
private boolean running;
private int order = 1;
@Override
public void setServletContext(ServletContext servletContext) {
this.servletContext = servletContext;
}
@Override
public void start() {
// 启动一个线程
new Thread(new Runnable() {
@Override
public void run() {
try {
//初始化EurekaServer，同时启动Eureka Server
eurekaServerBootstrap.contextInitialized(EurekaServerInitializerConfiguration.this.servletContext);
log.info("Started Eureka Server");
// 发布EurekaServer的注册事件
publish(new EurekaRegistryAvailableEvent(getEurekaServerConfig()));
// 设置启动的状态为true
EurekaServerInitializerConfiguration.this.running = true;
// 发布Eureka Start 事件，另外还有其他事件，我们可以根据需要监听这些事件，然后做一些特定的业务需求
publish(new EurekaServerStartedEvent(getEurekaServerConfig()));
}
catch (Exception ex) {
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);
}
.................省略...............
}
eurekaServerBootstrap是spring cloud定义的类，其代码完全拷贝了Eureka启动类的实现。 这里看到在Eureka启动后，会向外发送EurekaRegistryAvailableEvent 和 EurekaServerStartedEvent 事件，我们可以根据需要订阅这两个事件，做具体的处理操作。
接着我们一下 EurekaServerBootstrap 做了哪些具体的操作，从源码中可以看到方法 contextInitialized(ServletContext context) 进行了环境和上下文的初始化工作，下面我们分别看一下：
EurekaServerBootstrap > contextInitialized
public void contextInitialized(ServletContext context) {
try {
//初始化执行环境
initEurekaEnvironment();
//初始化上下文
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);
}
}
EurekaServerBootstrap > contextInitialized > initEurekaEnvironment
protected void initEurekaEnvironment() throws Exception {
log.info("Setting the eureka configuration..");
//设置数据中心
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);
}
//设置 Eureka 环境
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);
}
}
EurekaServerBootstrap > contextInitialized > initEurekaEnvironment
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");
// 从邻近的eureka节点复制注册表
int registryCount = this.registry.syncUp();
this.registry.openForTraffic(this.applicationInfoManager, registryCount);
// 注册所有监控统计信息
EurekaMonitors.registerAllStats();
}
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等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。