Spring Cloud - Eureka Client源码分析
准备做个Spring Cloud源码分析系列, 作为Spring Cloud的源码分析笔记.
这一篇是Eureka的客户端.
客户端
两种方式, 最终的实现基本一样.
显示指定服务发现的实现类型
使用@EnableEurekaClient注解显示的指定使用Eureka作为服务发现的实现, 并实例化EurekaClient实例. 实际上使用的是@EnableDiscoveryClient注解.
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@EnableDiscoveryClient
public @interface EnableEurekaClient {
}
动态配置实现
使用@EnableDiscoveryClient注解来配置服务发现的实现.
源码分析
EnableDiscoveryClient
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(EnableDiscoveryClientImportSelector.class)
public @interface EnableDiscoveryClient {
}
EnableDiscoveryClient注解的作用主要是用来引入EnableDiscoveryClientImportSelector
EnableDiscoveryClientImportSelector
@Order(Ordered.LOWEST_PRECEDENCE - 100)
public class EnableDiscoveryClientImportSelector
extends SpringFactoryImportSelector<EnableDiscoveryClient> {
@Override
protected boolean isEnabled() {
return new RelaxedPropertyResolver(getEnvironment()).getProperty(
"spring.cloud.discovery.enabled", Boolean.class, Boolean.TRUE);
}
@Override
protected boolean hasDefaultFactory() {
return true;
}
}
EnableDiscoveryClientImportSelector继承了SpringFactoryImportSelector并指定了泛型EnableDiscoveryClient. 这里的泛型是重点.
SpringFactoryImportSelector
public abstract class SpringFactoryImportSelector<T>
implements DeferredImportSelector, BeanClassLoaderAware, EnvironmentAware {
private ClassLoader beanClassLoader;
private Class<T> annotationClass;
protected SpringFactoryImportSelector() {
this.annotationClass = (Class<T>) GenericTypeResolver
.resolveTypeArgument(this.getClass(), SpringFactoryImportSelector.class);
}
public String[] selectImports(AnnotationMetadata metadata) {
...
}
}
这里只截取了部分变量和方法
SpringFactoryImportSelector是spring cloud common包中的一个抽象类, 主要作用是检查泛型T是否有指定的factory实现, 即spring.factories中有对应类的配置.
spring.factories
在spring-cloud-netflix-eureka-client.jar!/META-INF/spring.factories中EnableDiscoveryClient的指定factory实现是
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.cloud.netflix.eureka.config.EurekaClientConfigServerAutoConfiguration,\
org.springframework.cloud.netflix.eureka.config.EurekaDiscoveryClientConfigServiceAutoConfiguration,\
org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration,\
org.springframework.cloud.netflix.ribbon.eureka.RibbonEurekaAutoConfiguration
org.springframework.cloud.bootstrap.BootstrapConfiguration=\
org.springframework.cloud.netflix.eureka.config.EurekaDiscoveryClientConfigServiceBootstrapConfiguration
org.springframework.cloud.client.discovery.EnableDiscoveryClient=\
org.springframework.cloud.netflix.eureka.EurekaDiscoveryClientConfiguration
同时EnableAutoConfiguration中包含了org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration, EurekaClientAutoConfiguration会为EurekaDiscoveryClientConfiguration的实例依赖进行初始化, 如EurekaClient. EurekaClient在构造时会启动一个HeartBeat线程, 线程在运行的时候会做renew的操作, 将Application的信息注册更新到Eureka的服务端.
EurekaDiscoveryClientConfiguration
@Configuration
@EnableConfigurationProperties
@ConditionalOnClass(EurekaClientConfig.class)
@ConditionalOnProperty(value = "eureka.client.enabled", matchIfMissing = true)
@CommonsLog
public class EurekaDiscoveryClientConfiguration implements SmartLifecycle, Ordered {
...
}
