Spring - Bean 的初始化过程

---

1、创建一个Bean

@Component
public class OnBean {
}

2、让该Bean 实现Spring 的一些钩子函数

@Slf4j
@Component
public class OnBean
    implements BeanNameAware,
        BeanFactoryAware,
        ApplicationContextAware,
        BeanPostProcessor,
        InitializingBean,
        DisposableBean {

  private String beanName;
  private BeanFactory beanFactory;
  private ApplicationContext applicationContext;

  @Override
  public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
    log.info("ApplicationContextAware.setApplicationContext");
    this.applicationContext = applicationContext;
  }

  @Override
  public void setBeanName(String s) {
    log.info("BeanNameAware.setBeanName");
    this.beanName = s;
  }

  @Override
  public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
    log.info("BeanFactoryAware.setBeanFactory");
    this.beanFactory = beanFactory;
  }

  @Override
  public void destroy() throws Exception {
    log.info("DisposableBean.destroy");
  }

  @Override
  public void afterPropertiesSet() throws Exception {
    log.info("InitializingBean.afterPropertiesSet");
  }

  @Override
  public Object postProcessBeforeInitialization(Object bean, String beanName)
      throws BeansException {
    // log.info("所有bean 都会调用本方法 post Process Before Initialization");
    return null;
  }

  @Override
  public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
    // log.info("所有bean 都会调用本方法 post Process After Initialization");
    return null;
  }

  @PostConstruct
  void init() {
    log.info("init");
  }

  @PreDestroy
  void destory() {
    log.info("destory");
  }
}

3、追踪bean 的初始化过程

2019-09-01 22:08:33.134  INFO 68840 --- [           main] com.wretchant.timer.OnBean               : BeanNameAware.setBeanName
2019-09-01 22:08:33.134  INFO 68840 --- [           main] com.wretchant.timer.OnBean               : BeanFactoryAware.setBeanFactory
2019-09-01 22:08:33.134  INFO 68840 --- [           main] com.wretchant.timer.OnBean               : ApplicationContextAware.setApplicationContext
2019-09-01 22:08:33.134  INFO 68840 --- [           main] com.wretchant.timer.OnBean               : init
2019-09-01 22:08:33.135  INFO 68840 --- [           main] com.wretchant.timer.OnBean               : InitializingBean.afterPropertiesSet

执行顺序

• BeanNameAware.setBeanName
• BeanFactoryAware.setBeanFactory
• ApplicationContextAware.setApplicationContext
• @PostConstruct
• InitializingBean.afterPropertiesSet
• BeanPostProcessor.postProcessBeforeInitialization
• BeanPostProcessor.postProcessAfterInitialization

销毁时

2019-09-01 22:13:10.272  INFO 111588 --- [       Thread-5] com.wretchant.timer.OnBean               : destory
2019-09-01 22:13:10.272  INFO 111588 --- [       Thread-5] com.wretchant.timer.OnBean               : DisposableBean.destroy

执行顺序

• @PreDestroy
• DisposableBean.destroy

4、Spring 初始化 Bean 的源码

	/**
	 * Initialize the given bean instance, applying factory callbacks
	 * as well as init methods and bean post processors.
	 * <p>Called from {@link #createBean} for traditionally defined beans,
	 * and from {@link #initializeBean} for existing bean instances.
	 * @param beanName the bean name in the factory (for debugging purposes)
	 * @param bean the new bean instance we may need to initialize
	 * @param mbd the bean definition that the bean was created with
	 * (can also be {@code null}, if given an existing bean instance)
	 * @return the initialized bean instance (potentially wrapped)
	 * @see BeanNameAware
	 * @see BeanClassLoaderAware
	 * @see BeanFactoryAware
	 * @see #applyBeanPostProcessorsBeforeInitialization
	 * @see #invokeInitMethods
	 * @see #applyBeanPostProcessorsAfterInitialization
	 */
	protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
		if (System.getSecurityManager() != null) {
			AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
				invokeAwareMethods(beanName, bean);
				return null;
			}, getAccessControlContext());
		}
		else {
			invokeAwareMethods(beanName, bean);
		}

		Object wrappedBean = bean;
		if (mbd == null || !mbd.isSynthetic()) {
			wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
		}

		try {
			invokeInitMethods(beanName, wrappedBean, mbd);
		}
		catch (Throwable ex) {
			throw new BeanCreationException(
					(mbd != null ? mbd.getResourceDescription() : null),
					beanName, "Invocation of init method failed", ex);
		}
		if (mbd == null || !mbd.isSynthetic()) {
			wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
		}

		return wrappedBean;
	}