DefaultListableBeanFactory

DefaultListableBeanFactory 是一个完整的、功能成熟的 IoC 容器，如果你的需求很简单，甚至可以直接使用 DefaultListableBeanFactory，如果你的需求比较复杂，那么通过扩展 DefaultListableBeanFactory 的功能也可以达到，可以说 DefaultListableBeanFactory 是整个 Spring IoC 容器的始祖。

新建两个实体类User和UserMessage类和一个配置类MyConfig

@Data
@AllArgsConstructor
@NoArgsConstructor
public class UserMessage {private String phone;private String address;
}@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {private String username;@Autowiredprivate UserMessage userMessage;
}public class MyConfig {@Beanpublic User user(){return new User();}@Beanpublic UserMessage userMessage(){return new UserMessage("17860397188","123456");}
}

 动态注册 Bean，这是 DefaultListableBeanFactory 的功能之一，不过准确来说应该是动态注册 BeanDefinition 。

DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();AbstractBeanDefinition beanDefinition = BeanDefinitionBuilder.genericBeanDefinition(MyConfig.class).getBeanDefinition();beanFactory.registerBeanDefinition("config",beanDefinition);AnnotationConfigUtils.registerAnnotationConfigProcessors(beanFactory); //为beanfactory添加后处理器//beanfactory 后处理器解析@Bean等注解Map<String, BeanFactoryPostProcessor> beansOfType = beanFactory.getBeansOfType(BeanFactoryPostProcessor.class);beansOfType.values().forEach(i->i.postProcessBeanFactory(beanFactory));//Bean后处理器，针对Bean生命周期的各个阶段提供扩展，例如@AutowiredbeanFactory.getBeansOfType(BeanPostProcessor.class).values().forEach(beanFactory::addBeanPostProcessor);Arrays.stream(beanFactory.getBeanDefinitionNames()).forEach(i-> System.out.println(i));User user = (User) beanFactory.getBean("user");System.out.println(user.getUserMessage());

Bean 的懒加载。这个时候先把 BeanDefinition 定义好，等到真正调用 Bean 的时候，才会去初始化 Bean。在 DefaultListableBeanFactory 中还有一个 preInstantiateSingletons 方法可以提前注册 Bean，该方法是在 ConfigurableListableBeanFactory 接口中声明的，DefaultListableBeanFactory 类实现了 ConfigurableListableBeanFactory 接口并实现了接口中的方法。

@Override
public void preInstantiateSingletons() throws BeansException {if (logger.isTraceEnabled()) {logger.trace("Pre-instantiating singletons in " + this);}// Iterate over a copy to allow for init methods which in turn register new bean definitions.// While this may not be part of the regular factory bootstrap, it does otherwise work fine.List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);// Trigger initialization of all non-lazy singleton beans...for (String beanName : beanNames) {RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {if (isFactoryBean(beanName)) {Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);if (bean instanceof FactoryBean) {final FactoryBean<?> factory = (FactoryBean<?>) bean;boolean isEagerInit;if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>)((SmartFactoryBean<?>) factory)::isEagerInit,getAccessControlContext());}else {isEagerInit = (factory instanceof SmartFactoryBean &&((SmartFactoryBean<?>) factory).isEagerInit());}if (isEagerInit) {getBean(beanName);}}}else {getBean(beanName);}}}// Trigger post-initialization callback for all applicable beans...for (String beanName : beanNames) {Object singletonInstance = getSingleton(beanName);if (singletonInstance instanceof SmartInitializingSingleton) {final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;if (System.getSecurityManager() != null) {AccessController.doPrivileged((PrivilegedAction<Object>) () -> {smartSingleton.afterSingletonsInstantiated();return null;}, getAccessControlContext());}else {smartSingleton.afterSingletonsInstantiated();}}}
}