Bean的生命周期

理解Bean生命周期对于掌握Spring框架至关重要，它定义了Bean从创建到销毁的完整过程。

生命周期四个阶段

实例化 → 属性赋值 → 初始化 → 销毁

完整生命周期流程

1. 实例化 Bean
       ↓
2. 属性赋值（依赖注入）
       ↓
3. 处理 Aware 接口
   - BeanNameAware
   - BeanFactoryAware
   - ApplicationContextAware
       ↓
4. BeanPostProcessor.postProcessBeforeInitialization()
       ↓
5. 初始化方法
   - @PostConstruct
   - InitializingBean.afterPropertiesSet()
   - init-method
       ↓
6. BeanPostProcessor.postProcessAfterInitialization()
       ↓
7. Bean 就绪，可使用
       ↓
8. 销毁方法
   - @PreDestroy
   - DisposableBean.destroy()
   - destroy-method

代码示例

定义Bean

@Component
public class LifecycleBean implements BeanNameAware, InitializingBean, DisposableBean {

    private String beanName;

    // 1. 实例化（构造器）
    public LifecycleBean() {
        System.out.println("1. 构造器执行");
    }

    // 2. 属性赋值（依赖注入）
    @Autowired
    public void setOtherBean(OtherBean otherBean) {
        System.out.println("2. 属性赋值");
    }

    // 3. BeanNameAware回调
    @Override
    public void setBeanName(String name) {
        this.beanName = name;
        System.out.println("3. BeanNameAware: " + name);
    }

    // 4. @PostConstruct初始化
    @PostConstruct
    public void init() {
        System.out.println("4. @PostConstruct初始化");
    }

    // 5. InitializingBean回调
    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("5. InitializingBean.afterPropertiesSet()");
    }

    // 6. 自定义init-method
    public void customInit() {
        System.out.println("6. customInit()");
    }

    // 7. @PreDestroy销毁
    @PreDestroy
    public void preDestroy() {
        System.out.println("7. @PreDestroy销毁");
    }

    // 8. DisposableBean回调
    @Override
    public void destroy() throws Exception {
        System.out.println("8. DisposableBean.destroy()");
    }

    // 9. 自定义destroy-method
    public void customDestroy() {
        System.out.println("9. customDestroy()");
    }
}

BeanPostProcessor

@Component
public class CustomBeanPostProcessor implements BeanPostProcessor {

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) {
        System.out.println("BeanPostProcessor前置处理: " + beanName);
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) {
        System.out.println("BeanPostProcessor后置处理: " + beanName);
        return bean;
    }
}

初始化方法对比

销毁方法对比

XML配置方式

<bean id="lifecycleBean"
      class="com.example.LifecycleBean"
      init-method="customInit"
      destroy-method="customDestroy"/>

Aware接口说明

要点总结

1. 生命周期四阶段：实例化、属性赋值、初始化、销毁
2. 初始化方法执行顺序：@PostConstruct → InitializingBean → init-method
3. 销毁方法执行顺序：@PreDestroy → DisposableBean → destroy-method
4. BeanPostProcessor在初始化前后执行，常用于AOP代理创建
5. 推荐使用注解方式（@PostConstruct/@PreDestroy）更简洁