003-Spring4 扩展分析-spring类初始化@PostConstruct > InitializingBean > init-method、ApplicationContext、BeanPostProcessor、BeanFactoryPostProcessor、BeanDefinitionRegistryPostProcessor

一、spring类初始化@PostConstruct > InitializingBean > init-method

　　InitializingBean接口为bean提供了初始化方法的方式，它只包括afterPropertiesSet方法，凡是继承该接口的子类，在初始化bean的时候会执行该方法。

示例

<bean id="myInitializingBean" class="com.paic.phssp.springtest.init.MyInitializingBean" init-method="testInit"></bean>

bean

/**
 * 继承InitializingBean接口的类，在初始化bean的时候会执行该方法
 */
//@Component
public class MyInitializingBean implements InitializingBean {

    public MyInitializingBean() {
        System.out.println("1MyInitializingBean....");
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("3ceshi MyInitializingBean>>>>>>>>>>>>>>>>>>>");
    }

    @PostConstruct  //功能上近似init-method，但加载时机不同
    public void test(){
        System.out.println("2PostConstruct >>>>>>>>>>>>");
    }

    public void testInit(){
        System.out.println("4ceshi init-method");
    }
}

结果：

1MyInitializingBean....
2PostConstruct >>>>>>>>>>>>
3ceshi MyInitializingBean>>>>>>>>>>>>>>>>>>>
4ceshi init-method

说明：

　　通过上述输出结果，三者的先后顺序：Constructor > @PostConstruct > InitializingBean > init-method

1.1、 InitializingBean > init-method 执行时机

　　spring初始化bean过程

　　002-创建型-03-单例模式（Singleton）【7种】、spring单例及原理  spring 单例

　　通过查看spring的加载bean的源码类(AbstractAutowireCapableBeanFactory)可看出

　　如使用getBean方式创建：getBean→doGetBean→createBean→doCreateBean→initializeBean→invokeInitMethods

　　查看AbstractAutowireCapableBeanFactory.invokeInitMethods

    protected void invokeInitMethods(String beanName, final Object bean, @Nullable RootBeanDefinition mbd)
            throws Throwable {

        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>) () -> {
                        ((InitializingBean) bean).afterPropertiesSet();
                        return null;
                    }, getAccessControlContext());
                }
                catch (PrivilegedActionException pae) {
                    throw pae.getException();
                }
            }
            else {
                ((InitializingBean) bean).afterPropertiesSet();
            }
        }

        if (mbd != null && bean.getClass() != NullBean.class) {
            String initMethodName = mbd.getInitMethodName();
            if (StringUtils.hasLength(initMethodName) &&
                    !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
                    !mbd.isExternallyManagedInitMethod(initMethodName)) {
                invokeCustomInitMethod(beanName, bean, mbd);
            }
        }
    }

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