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 {

    @Override
    public 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);
    }

    @Override
    public 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);

	}

}