一般我们Server端会像下图一样，引入Eureka，下面就通过这个来分析Eureka服务端源码流程
1、自动配置
@EnableEurekaServer开关
eureka是一个c/s架构的服务治理框架，springcloud将其集成用作服务治理。springcloud使用eureka比较简单，只需要引入依赖以后添加一个@EnableEurekaServer注解即可，如
@SpringBootApplication
@EnableEurekaServer
public class EurekaApplication {
public static void main(String[] args) {
SpringApplication.run(EurekaApplication.class, args);
}
}
@EnableEurekaServer又有什么魔力呢？为什么它能够开关EurekaServer？为此，我们打开@EnableEurekaServer注解
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(EurekaServerMarkerConfiguration.class)
public @interface EnableEurekaServer {
}
可以看到，@EnableEurekaServer的@Import注解导入了一个EurekaServerMarkerConfiguration类。所以，开启@EnableEurekaServer注解也就是导入该类。
那么，EurekaServerMarkerConfiguration这个配置类又做了啥？
@Configuration
public class EurekaServerMarkerConfiguration {
@Bean
public Marker eurekaServerMarkerBean() {
return new Marker();
}
class Marker {
}
}
可以看到，这里只是把一个空的Marker类变成了spring中的Bean。而Marker本身什么功能都没有实现。顾名思义，我们可以这样猜测一下：@EnableEurekaServer注解就是将Marker配置为Bean，而Marker作为Bean的存在，将会触发自动配置，从而达到了一个开关的效果。
EurekaServerAutoConfiguration自动配置类
我们再打开EurekaServerAutoConfiguration这个自动配置类
@Configuration
@Import(EurekaServerInitializerConfiguration.class)
@ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class)
@EnableConfigurationProperties({ EurekaDashboardProperties.class,
InstanceRegistryProperties.class })
@PropertySource(“classpath:/eureka/server.properties”)
public class EurekaServerAutoConfiguration implements WebMvcConfigurer {
// …
}
首先值得注意的是@ConditionalOnBean这个注解，它将判断EurekaServerMarkerConfiguration.Marker这个Bean是否存在。如果存在才会解析这个自动配置类，从而呼应了@EnableEurekaServer这个注解的功能。
@EnableConfigurationProperties注解和@PropertySource注解都加载了一些键值对的属性。
@Import导入了一个初始化类EurekaServerInitializerConfiguration（后面再看它）
EurekaServerAutoConfiguration作为自动配置类，我们看看它主要配置了哪些东西（有所忽略）
看板
服务治理少不了需要一个DashBoard来可视化监控，EurekaController基于springmvc提供DashBoard相关的功能。
@Bean
@ConditionalOnProperty(prefix = “eureka.dashboard”, name = “enabled”,
matchIfMissing = true)
public EurekaController eurekaController() {
return new EurekaController(this.applicationInfoManager);
}
发现注册
发现注册作为主要的核心功能，也是必不可少的
@Bean
public PeerAwareInstanceRegistry peerAwareInstanceRegistry(
ServerCodecs serverCodecs) {
this.eurekaClient.getApplications(); // force initialization
return new InstanceRegistry(this.eurekaServerConfig, this.eurekaClientConfig,
serverCodecs, this.eurekaClient,
this.instanceRegistryProperties.getExpectedNumberOfClientsSendingRenews(),
this.instanceRegistryProperties.getDefaultOpenForTrafficCount());
}
启动引导
@Bean
public EurekaServerBootstrap eurekaServerBootstrap(PeerAwareInstanceRegistry registry,
EurekaServerContext serverContext) {
return new EurekaServerBootstrap(this.applicationInfoManager,
this.eurekaClientConfig, this.eurekaServerConfig, registry,
serverContext);
}
Jersey提供rpc调用
jersey是一个restful风格的基于http的rpc调用框架，eureka使用它来为客户端提供远程服务。
@Bean
public javax.ws.rs.core.Application jerseyApplication(Environment environment,
ResourceLoader resourceLoader) {
ClassPathScanningCandidateComponentProvider provider = new ClassPathScanningCandidateComponentProvider(
false, environment);
// Filter to include only classes that have a particular annotation.
//
provider.addIncludeFilter(new AnnotationTypeFilter(Path.class));
provider.addIncludeFilter(new AnnotationTypeFilter(Provider.class));
// Find classes in Eureka packages (or subpackages)
//
Set<Class<?>> classes = new HashSet<>();
for (String basePackage : EUREKA_PACKAGES) {
Set<BeanDefinition> beans = provider.findCandidateComponents(basePackage);
for (BeanDefinition bd : beans) {
Class<?> cls = ClassUtils.resolveClassName(bd.getBeanClassName(),
resourceLoader.getClassLoader());
classes.add(cls);
}
}
// Construct the Jersey ResourceConfig
Map<String, Object> propsAndFeatures = new HashMap<>();
propsAndFeatures.put(
// Skip static content used by the webapp
ServletContainer.PROPERTY_WEB_PAGE_CONTENT_REGEX,
EurekaConstants.DEFAULT_PREFIX + "/(fonts|images|css|js)/.*");
DefaultResourceConfig rc = new DefaultResourceConfig(classes);
rc.setPropertiesAndFeatures(propsAndFeatures);
return rc;
}
这里将会扫描Resource，并添加到ResourceConfig当中。
EurekaServerInitializerConfiguration初始化
再回过头来，看看@EnableEurekaServer注解导入的EurekaServerInitializerConfiguration类。
@Configuration
public class EurekaServerInitializerConfiguration implements ServletContextAware, SmartLifecycle, Ordered {
// …
@Override
public void start() {
new Thread(() -> {
try {
eurekaServerBootstrap.contextInitialized(EurekaServerInitializerConfiguration.this.servletContext);
publish(new EurekaRegistryAvailableEvent(getEurekaServerConfig()));
EurekaServerInitializerConfiguration.this.running = true;
publish(new EurekaServerStartedEvent(getEurekaServerConfig()));
} catch (Exception ex) {
//
}
}).start();
}
}
初始化过程调用了EurekaServerBootstrap的contextInitialized方法，我们跟进看看
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);
}
}
这里初始化了EurekaEnvironment和EurekaServerContext，EurekaEnvironment无非就是设置了各种配置之类的东西。我们打开initEurekaServerContext看看
protected void initEurekaServerContext() throws Exception {
// …
// Copy registry from neighboring eureka node
int registryCount = this.registry.syncUp();
this.registry.openForTraffic(this.applicationInfoManager, registryCount);
// Register all monitoring statistics.
EurekaMonitors.registerAllStats();
}
这里主要做了两件事：
1）从相邻的集群节点当中同步注册信息
2）注册一个统计器
回到顶部
总结
@EnableEurekaServer注解开启了EurekaServerAutoConfiguration这个配置类的解析，EurekaServerAutoConfiguration这个配置了主要准备了看板、注册发现、启动引导、Jersey等，EurekaServerInitializerConfigration将会触发启动引导，引导过程会从其它Eureka集群节点当中同步注册信息。