Springboot自动装配整理

首先写一个咱们本身的HelloWorld配置类

一、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代码写一个咱们本身的标签

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

@EnableFeignClients Import的是FeignClientsRegistrar.class，而咱们这里导入的是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

二、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，经过@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中全部的属性方法，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<String,Object> annotationAttributes = importingClassMetadata
                .getAnnotationAttributes(EnableServer.class.getName());
        //获取名为type的属性方法，而且强制转换成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便可

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);
        //建立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...