一、eureka服務端自動配置

所有文章

https://www.cnblogs.com/lay2017/p/11908715.html

 

正文

@EnableEurekaServer開關

eureka是一個c/s架構的服務治理框架，springcloud將其集成用作服務治理。springcloud使用eureka比較簡單，只需要引入依賴以后添加一個@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？為什么它能夠開關EurekaServer？為此，我們打開@EnableEurekaServer注解

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

}

可以看到，@EnableEurekaServer的@Import注解導入了一個EurekaServerMarkerConfiguration類。所以，開啟@EnableEurekaServer注解也就是導入該類。

 

那么，EurekaServerMarkerConfiguration這個配置類又做了啥？

@Configuration
public class EurekaServerMarkerConfiguration {

    @Bean
    public Marker eurekaServerMarkerBean() {
        return new Marker();
    }

    class Marker {

    }
}

可以看到，這里只是把一個空的Marker類變成了spring中的Bean。而Marker本身什么功能都沒有實現。顧名思義，我們可以這樣猜測一下：@EnableEurekaServer注解就是將Marker配置為Bean，而Marker作為Bean的存在，將會觸發自動配置，從而達到了一個開關的效果。

 

EurekaServerAutoConfiguration自動配置類

我們再打開EurekaServerAutoConfiguration這個自動配置類

@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這個注解，它將判斷EurekaServerMarkerConfiguration.Marker這個Bean是否存在。如果存在才會解析這個自動配置類，從而呼應了@EnableEurekaServer這個注解的功能。

@EnableConfigurationProperties注解和@PropertySource注解都加載了一些鍵值對的屬性。

@Import導入了一個初始化類EurekaServerInitializerConfiguration（后面再看它）

 

EurekaServerAutoConfiguration作為自動配置類，我們看看它主要配置了哪些東西（有所忽略）

看板

服務治理少不了需要一個DashBoard來可視化監控，EurekaController基於springmvc提供DashBoard相關的功能。

@Bean
@ConditionalOnProperty(prefix = "eureka.dashboard", name = "enabled",
        matchIfMissing = true)
public EurekaController eurekaController() {
    return new EurekaController(this.applicationInfoManager);
}

 

發現注冊

發現注冊作為主要的核心功能，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());
}

 

啟動引導

@Bean
public EurekaServerBootstrap eurekaServerBootstrap(PeerAwareInstanceRegistry registry,
        EurekaServerContext serverContext) {
    return new EurekaServerBootstrap(this.applicationInfoManager,
            this.eurekaClientConfig, this.eurekaServerConfig, registry,
            serverContext);
}

 

Jersey提供rpc調用

jersey是一個restful風格的基於http的rpc調用框架，eureka使用它來為客戶端提供遠程服務。

@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;
}

這里將會掃描Resource，並添加到ResourceConfig當中。

 

EurekaServerInitializerConfiguration初始化

再回過頭來，看看@EnableEurekaServer注解導入的EurekaServerInitializerConfiguration類。

@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();
    }

}

初始化過程調用了EurekaServerBootstrap的contextInitialized方法，我們跟進看看

 

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);
    }
}

這里初始化了EurekaEnvironment和EurekaServerContext，EurekaEnvironment無非就是設置了各種配置之類的東西。我們打開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();
}

這里主要做了兩件事：

1）從相鄰的集群節點當中同步注冊信息

2）注冊一個統計器

 

總結

@EnableEurekaServer注解開啟了EurekaServerAutoConfiguration這個配置類的解析，EurekaServerAutoConfiguration這個配置了主要准備了看板、注冊發現、啟動引導、Jersey等，EurekaServerInitializerConfigration將會觸發啟動引導，引導過程會從其它Eureka集群節點當中同步注冊信息。