Bean 的生命周期

IoC 容器的操作流程

IoC 中最重要的方法是 refresh 方法，其中规范了整个容器的创建流程。其实主要的就那么几步：

1. 加载 BeanDefinition
2. 执行 BeanFactoryPostProcessor 修改 BeanFactory
3. 注册 BeanPostProcessor
4. 创建出一个观察者模式
5. 实例化单例 Bean
6. Bean 创建完成事件广播

Spring流程

Bean 对象的创建流程

bean创建流程

public abstract class AbstractBeanFactory {
    @Override
    public Object getBean(String name) throws BeansException {
        // 真正的操作都是在 doXXX 中实现的
       return doGetBean(name, null);
    }

    protected <T> T doGetBean(final String name, final Object[] args) {
        Object sharedInstance = getSingleton(name);
        if (sharedInstance != null) {
            // 如果是 FactoryBean，则需要调用 FactoryBean#getObject
            return (T) getObjectForBeanInstance(sharedInstance, name);
        }
        // 从BeanFactory中获取目标的BeanDefinition信息
        BeanDefinition beanDefinition = getBeanDefinition(name);
        // 抽象方法 由AbstractAutowireCapableBeanFactory实现
        Object bean = createBean(name, beanDefinition, args);
        return (T) getObjectForBeanInstance(bean, name);
    }
}

public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFactory implements AutowireCapableBeanFactory {
    // 注册单例bean
    @Override
    protected Object createBean(String beanName, BeanDefinition beanDefinition, Object[] args) throws BeansException {
        Object bean = null;
        try {
            // 判断是否返回代理对象
            bean = resolveBeforeInstantiation(beanName, beanDefinition);
            if (null != bean) {
                return bean;
            }
            // 实例化bean
            bean = createBeanInstance(beanDefinition, beanName, args);
            // 在设置Bean属性前，允许 BeanPostProcessor 修改属性值
            // 但只能是InstantiationAwareBeanPostProcessor这个接口的
            applyBeanPostProcessorsBeforeApplyingPropertyValues(beanName, bean, beanDefinition);
            // 给 Bean 填充属性
            applyPropertyValues(beanName, bean, beanDefinition);
            // 执行Bean的初始化方法和 BeanPostProcessor 的前置后置方法
            bean = initializeBean(beanName, bean, beanDefinition);
        } catch (Exception e) {
            throw new BeansException("Instantiation of bean failed", e);
        }

        // 注册实现了 DisposableBean 接口的 Bean 对象,将其保存到需要销毁bean的集合中
        registerDisposableBeanIfNecessary(beanName, bean, beanDefinition);

        // DefaultSingletonBeanRegistry.registerSingleton()
        // 单例Bean和多例Bean的区别：是否把其放到内存中，及是否调用 registerSingleton()
        if (beanDefinition.isSingleton()) {
            registerSingleton(beanName, bean);
        }
        return bean;
    }

    protected void applyBeanPostProcessorsBeforeApplyingPropertyValues(String beanName, Object bean, BeanDefinition beanDefinition) {
        for (BeanPostProcessor beanPostProcessor : getBeanPostProcessors()) {
            if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
                PropertyValues pvs = ((InstantiationAwareBeanPostProcessor) beanPostProcessor).postProcessPropertyValues(beanDefinition.getPropertyValues(), bean, beanName);
                if (null != pvs) {
                    for (PropertyValue propertyValue : pvs.getPropertyValues()) {
                        beanDefinition.getPropertyValues().addPropertyValue(propertyValue);
                    }
                }
            }
        }
    }

    private Object initializeBean(String beanName, Object bean, BeanDefinition beanDefinition) {
        // 如果目标Bean实现了Aware接口，先添加Aware功能
        if (bean instanceof Aware) {
            if (bean instanceof BeanFactoryAware) {
                ((BeanFactoryAware) bean).setBeanFactory(this);
            }
            if (bean instanceof BeanClassLoaderAware) {
                ((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader());
            }
            if (bean instanceof BeanNameAware) {
                ((BeanNameAware) bean).setBeanName(beanName);
            }
        }
        // 1. 执行 BeanPostProcessor Before处理
        Object wrappedBean = applyBeanPostProcessorsBeforeInitialization(bean, beanName);
        // 执行 Bean 对象的初始化方法
        try {
            invokeInitMethods(beanName, wrappedBean, beanDefinition);
        } catch (Exception e) {
            throw new BeansException("Invocation of init method of bean[" + beanName + "] failed", e);
        }

        // 2. 执行 BeanPostProcessor After 处理
        // AOP功能在这里添加
        wrappedBean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
        return wrappedBean;
    }

    private void invokeInitMethods(String beanName, Object bean, BeanDefinition beanDefinition) throws Exception {
        // 1. 如果实现接口 InitializingBean
        if (bean instanceof InitializingBean) {
            ((InitializingBean) bean).afterPropertiesSet();
        }
        // 2. 下面的initMethod方法就是xml配置中的 init-method
        String initMethodName = beanDefinition.getInitMethodName();
        if (StrUtil.isNotEmpty(initMethodName) && !(bean instanceof InitializingBean)) {
            Method initMethod = beanDefinition.getBeanClass().getMethod(initMethodName);
            if (null == initMethod) {
                throw new BeansException("Could not find an init method named '" + initMethodName + "' on bean with name '" + beanName + "'");
            }
            initMethod.invoke(bean);
        }
    }
}