SpringBoot复习：（20）如何把bean手动注册到容器？

可以通过实现BeanDefinitionRegistryPostProcessor接口，它的父接口是BeanFactoryPostProcessor.
步骤：
一、自定义一个组件类：

package com.example.demo.service;public class MusicService {public MusicService() {System.out.println("music service constructed!");}
}

二、定义类实现BeanDefinitionRegistryPostProcessor:

package com.example.demo.component;import com.example.demo.service.MusicService;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.beans.factory.support.RootBeanDefinition;
import org.springframework.stereotype.Component;@Component
public class MyBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {@Overridepublic void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {System.out.println(registry.getBeanDefinitionCount());//定义BeanDefinition对象RootBeanDefinition rootBeanDefinition = new RootBeanDefinition(MusicService.class);//将BeanDefinition对象注册到容器registry.registerBeanDefinition("musicBean", rootBeanDefinition);}@Overridepublic void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {System.out.println( beanFactory.getBeanDefinitionCount() );}
}

通过@Component注解，Spring就能够扫描到MyBeanDefinitionRegistryPostProcessor,也就能够把MusicService这个组件注册到容器。
三、可以获取在容器中通过MyBeanDefinitionRegistryPostProcessor注册的bean

package com.example.demo;import com.example.demo.service.MusicService;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.PropertySource;@SpringBootApplication
@PropertySource("classpath:my.properties")
public class DemoApplication {public static void main(String[] args) {ConfigurableApplicationContext context = SpringApplication.run(DemoApplication.class, args);System.out.println("abc");MusicService musicService = context.getBean("musicBean", MusicService.class);System.out.println(musicService);}}