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; @Autowired private UserMessage userMessage; } public class MyConfig { @Bean public User user(){ return new User(); } @Bean public 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@Autowired beanFactory.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(); } } } }
