InitializingBean接口

package org.springframework.beans.factory;

/**
 *  //由bean实现的接口，一旦bean工厂设置了它们的所有属性，就需要对其进行响应:
 *	例如，执行定制初始化，或检查所有强制属性是否已设置。
 * Interface to be implemented by beans that need to react once all their
 * properties have been set by a BeanFactory: for example, to perform custom
 * initialization, or merely to check that all mandatory properties have been set.
 *
 * //实现InitializingBean的另一种方法是指定一个定制的init-方法，例如在XML bean定义中
 * <p>An alternative to implementing InitializingBean is specifying a custom
 * init-method, for example in an XML bean definition.
 * For a list of all bean lifecycle methods, see the
 * {@link BeanFactory BeanFactory javadocs}.
 *
 * @author Rod Johnson
 * @see BeanNameAware
 * @see BeanFactoryAware
 * @see BeanFactory
 * @see org.springframework.beans.factory.support.RootBeanDefinition#getInitMethodName
 * @see org.springframework.context.ApplicationContextAware
 */
public interface InitializingBean {

	/**
	 *//在BeanFactory设置了提供的所有bean属性后调用,
	 *//此方法允许bean实例仅在设置了所有bean属性之后才能执行初始化，并在配置错误时抛出异常。
	 *//在发生错误配置(如设置基本属性失败)或初始化失败的情况下会抛出Exception 
	 * Invoked by a BeanFactory after it has set all bean properties supplied
	 * (and satisfied BeanFactoryAware and ApplicationContextAware).
	 * <p>This method allows the bean instance to perform initialization only
	 * possible when all bean properties have been set and to throw an
	 * exception in the event of misconfiguration.
	 * @throws Exception in the event of misconfiguration (such
	 * as failure to set an essential property) or if initialization fails.
	 */
	void afterPropertiesSet() throws Exception;

}

        /**
         * 让bean有机会对其所有属性进行响应，并有机会了解其所属bean工厂(此对象).
         * 这意味着检查bean是否实现了InitializingBean或定义了自定义init方法，
         * 如果实现了，则调用必要的回调。
         */
	/**
	 * Give a bean a chance to react now all its properties are set,
	 * and a chance to know about its owning bean factory (this object).
	 * This means checking whether the bean implements InitializingBean or defines
	 * a custom init method, and invoking the necessary callback(s) if it does.
	 * @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 merged bean definition that the bean was created with
	 * (can also be {@code null}, if given an existing bean instance)
	 * @throws Throwable if thrown by init methods or by the invocation process
	 * @see #invokeCustomInitMethod
	 */
	protected void invokeInitMethods(String beanName, final Object bean, @Nullable RootBeanDefinition mbd)
			throws Throwable {
			
		//判断该bean是否实现了实现了InitializingBean接口，
		//如果实现了InitializingBean接口，则只掉调用bean的afterPropertiesSet方法
		boolean isInitializingBean = (bean instanceof InitializingBean);
		if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
			if (logger.isDebugEnabled()) {
				logger.debug("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
			}
			if (System.getSecurityManager() != null) {
				try {
					AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () -> {
						//调用afterPropertiesSet
						((InitializingBean) bean).afterPropertiesSet();
						return null;
					}, getAccessControlContext());
				}
				catch (PrivilegedActionException pae) {
					throw pae.getException();
				}
			}
			else {
				//调用afterPropertiesSet
				((InitializingBean) bean).afterPropertiesSet();
			}
		}

		if (mbd != null && bean.getClass() != NullBean.class) {
			String initMethodName = mbd.getInitMethodName();
			////判断是否指定了init-method方法，如果指定了init-method方法，则再调用制定的init-method
			if (StringUtils.hasLength(initMethodName) &&
					!(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
					!mbd.isExternallyManagedInitMethod(initMethodName)) {
				//查看该方法的源码，可以发现init-method方法中指定的方法是通过反射实现
				invokeCustomInitMethod(beanName, bean, mbd);
			}
		}
	}