首先写一个我们自己的HelloWorld配置类

1、基于"注解驱动"实现@Enable模块

@Configuration public class HelloWorldConfiguration {
@Bean
public String helloWorld() {
return "Hello,World";
}
}

再模仿Spring Cloud Feign源码解析 中的@EnableFeignClients代码写一个我们自己的标签

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented @Import(HelloWorldConfiguration.class)
public @interface EnableHelloWorld {
}

@EnableFeignClients Import的是FeignClientsRegistrar.class，而我们这里导入的是HelloWorldConfiguration.class

再编写一个引导类来看一下效果。

@EnableHelloWorld @Configuration public class EnabledHelloWorldBootstrap {
public static void main(String[] args) {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
context.register(EnabledHelloWorldBootstrap.class);
context.refresh();
String helloWorld = context.getBean("helloWorld", String.class);
System.out.printf("helloWorld = %s \n",helloWorld);
context.close();
}
}

运行结果(部分)

15:00:46.060 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Returning cached instance of singleton bean 'lifecycleProcessor'
15:00:46.065 [main] DEBUG org.springframework.core.env.PropertySourcesPropertyResolver - Could not find key 'spring.liveBeansView.mbeanDomain' in any property source
15:00:46.069 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Returning cached instance of singleton bean 'helloWorld'
helloWorld = Hello,World
15:00:46.069 [main] INFO org.springframework.context.annotation.AnnotationConfigApplicationContext - Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@31a5c39e: startup date [Thu Nov 21 15:00:45 CST 2019]; root of context hierarchy
15:00:46.070 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Returning cached instance of singleton bean 'lifecycleProcessor'
15:00:46.070 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Destroying singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@5427c60c: defining beans [org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.event.internalEventListenerProcessor,org.springframework.context.event.internalEventListenerFactory,enabledHelloWorldBootstrap,com.cloud.demo.config.HelloWorldConfiguration,helloWorld]; root of factory hierarchy

2、基于"接口编程"实现@Enable模块

基于ImportSelector接口实现

假设当前应用支持两种服务类型:HTTP和FTP，通过@EnableServer设置服务器类型(type)提供对应的服务

先定义一个服务接口

public interface Server {
/** * 启动服务器 */ void start();
/** * 关闭服务器 */ void stop();
/** * 服务器类型 */ enum Type {
HTTP, //HTTP服务器
FTP //FTP服务器
}
}

两个实现类

@Component public class HTTPServer implements Server {
@Override
public void start() {
System.out.println("HTTP服务器启动中...");
}

@Override

public void stop() {
System.out.println("HTTP服务器关闭中...");
}
}

@Component public class FTPServer implements Server {
@Override
public void start() {
System.out.println("FTP服务器启动中...");
}

@Override

public void stop() {
System.out.println("FTP服务器关闭中...");
}
}

实现@Enable模块驱动

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented @Import(ServerImportSelector.class)
public @interface EnableServer {
/** * 设置服务器类型 * @return */ Server.Type type(); }

实现Server ImportSelector接口

public class ServerImportSelector implements ImportSelector {
@Override
public String[] selectImports(AnnotationMetadata importingClassMetadata) {
//读取EnableServer中所有的属性方法，本例中仅有type()属性方法
//其中key为属性方法的名称，value为属性方法的返回对象 Map annotationAttributes = importingClassMetadata
.getAnnotationAttributes(EnableServer.class.getName());
//获取名为type的属性方法，并且强制转换成Server.Type类型
Server.Type type = (Server.Type) annotationAttributes.get("type");
//导入的类名称数组
String[] importClassNames = new String[0];
switch (type) {
case HTTP:
importClassNames = new String[]{HTTPServer.class.getName()};
break; case FTP:
importClassNames = new String[]{FTPServer.class.getName()};
break; }
return importClassNames;
}
}

标注@EnableServer到引导类EnableServerBootstrap

@Configuration @EnableServer(type = Server.Type.HTTP)
public class EnableServerBootstrap {
public static void main(String[] args) {
//构建Annotation配置驱动Spring上下文
AnnotationConfigApplicationContext context = new
AnnotationConfigApplicationContext();
//注册当前引导类(被@Configuration标注)到Spring上下文
context.register(EnableServerBootstrap.class);
//启动上下文
context.refresh();
//获取Server Bean对象，实际为HttpServer
Server server = context.getBean(Server.class);
//启动服务器
server.start();
//关闭服务器
server.stop();
}
}

运行结果(部分)

16:52:08.966 [main] DEBUG org.springframework.context.annotation.AnnotationConfigApplicationContext - Unable to locate LifecycleProcessor with name 'lifecycleProcessor': using default [org.springframework.context.support.DefaultLifecycleProcessor@2fb3536e]
16:52:08.967 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Returning cached instance of singleton bean 'lifecycleProcessor'
16:52:08.975 [main] DEBUG org.springframework.core.env.PropertySourcesPropertyResolver - Could not find key 'spring.liveBeansView.mbeanDomain' in any property source
16:52:08.979 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Returning cached instance of singleton bean 'com.cloud.demo.server.HTTPServer'
HTTP服务器启动中...
HTTP服务器关闭中...

基于ImportBeanDefinitionRegistrar接口实现

替换上例中的ServerImportSelector即可

public class ServerImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
//复用 {@link ServerImportSelector} 实现，避免重复劳动
ImportSelector importSelector = new ServerImportSelector();
//筛选Class名称集合
String[] selectedClassNames = importSelector.selectImports(importingClassMetadata);
//创建Bean定义
Stream.of(selectedClassNames)
//转化为BeanDefinitionBuilder对象
.map(BeanDefinitionBuilder::genericBeanDefinition)
//转化为BeanDefinition
.map(BeanDefinitionBuilder::getBeanDefinition)
//注册BeanDefinition到BeanDefinitionRegistry
.forEach(beanDefinition -> BeanDefinitionReaderUtils
.registerWithGeneratedName(beanDefinition,registry));
}
}

替换@EnableServer的@Import

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented @Import(ServerImportBeanDefinitionRegistrar.class)
public @interface EnableServer {
/** * 设置服务器类型 * @return */ Server.Type type(); }

运行结果

17:38:53.147 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Returning cached instance of singleton bean 'lifecycleProcessor'
17:38:53.150 [main] DEBUG org.springframework.core.env.PropertySourcesPropertyResolver - Could not find key 'spring.liveBeansView.mbeanDomain' in any property source
17:38:53.152 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Returning cached instance of singleton bean 'com.cloud.demo.server.HTTPServer#0'
HTTP服务器启动中...
HTTP服务器关闭中...

结束语

以往，配置和设置像数据库这样的服务可能需要数周时间，甚至更长的时间。通过使用云平台，组织可以在一个下午就建立数据库并将应用程序连接到该数据库。如引言中所述，这极大地提升了组织的敏捷性，让组织及其开发者可以专注于核心业务目标。

您在本练习中可能已经注意到一个问题，即，需要手动与 Kubernetes 进行大量交互。 尽管在这种小规模练习中这不算什么大问题，而且这对熟悉 Kubernetes 和 kubectl 很有用，但这在实际应用程序中会成为无法衡量的问题。在本系列教程的下一个教程中，我们将研究如何设置流水线以自动完成构建、测试和部署应用程序的过程。