Spring Bean生命周期-阶段汇总，面试必备(十二)

以后面试问到Bean的生命周期再也不怕了！

看了这么久的Spring源码，想必对Spring的生命周期已经有了一定的了解，这次将之前零散的生命周期处理的事情贯穿起来，看过之后，一定对bean的生命周期有更深入的理解

与文无关

简介

1. 实例化

2. 设置bean的Aware

3. BeanPostProcessor.postProcessBeforeInitialization(Object bean, String beanName)

4. InitializingBean.afterPorpertiesSet

5. BeanPostProcessor.postProcessAfterInitialization(Object bean, String beanName)

6. SmartInitializingSingleton.afterSingletonsInstantiated

7. SmartLifecycle.start

8. bean已经在spring容器的管理下，可以做我们想做的事

9. SmartLifecycle.stop(Runnable callback)

10. DisposableBean.destroy()

细节部分

1. 实例化对应代码，使用合适的初始化方案来创建一个新的bean实例，factory-method，或者构造器注入，或者简单的直接实例化

实例化策略类：
InstantiationStrategy

实例化具体方法：
AbstractAutowireCapableBeanFactory.createBeanInstance(String beanName, RootBeanDefinition mbd, Object[] args)

1. 设置bean的Aware。InitializingBean.afterPorpertiesSet，BeanPostProcessor对bean的加工处理基本上在一块出现。

设置Aware方法顺序：

• BeanNameAware

• BeanClassLoaderAware

• BeanFactoryAware

BeanPostProcessor.postProcessBeforeInitialization

image.png

ApplicationContextAwareProcessor也会设置Aware：

• EnvironmentAware

• EmbeddedValueResolverAware

• ResourceLoaderAware

• ApplicationEventPublisherAware

• MessageSourceAware

• ApplicationContextAware

调用afterpropertiesSet方法：位于AbstractAutowireCapableBeanFactory.invokeInitMethods(String beanName, final Object bean, RootBeanDefinition mbd)方法中

protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {        
      // 设置Aware  
        if (System.getSecurityManager() != null) {
            AccessController.doPrivileged(new PrivilegedAction<Object>() {                @Override
                public Object run() {
                    invokeAwareMethods(beanName, bean);                    return null;
                }
            }, getAccessControlContext());
        }        else {
            invokeAwareMethods(beanName, bean);
        }        
      //BeanPostProcessor的postProcessBeforeInitialization  
        Object wrappedBean = bean;        if (mbd == null || !mbd.isSynthetic()) {
            wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
        }        try {           //调用init方法，其判断是否是InitializingBean的实例，然后调用afterPropertiesSet
            invokeInitMethods(beanName, wrappedBean, mbd);
        }        catch (Throwable ex) {            throw new BeanCreationException(
                    (mbd != null ? mbd.getResourceDescription() : null),
                    beanName, "Invocation of init method failed", ex);
        }    
      //BeanPostProcessor的postProcessAfterInitialization  
        if (mbd == null || !mbd.isSynthetic()) {
            wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
        }        return wrappedBean;
    }

1. SmartInitializingSingleton.afterSingletonsInstantiated的调用位置

DefaultListableBeanFactory.preInstantiateSingletons方法，其在所有的bean都实例化完成之后调用

@Override
    public void preInstantiateSingletons() throws BeansException {        if (this.logger.isDebugEnabled()) {            this.logger.debug("Pre-instantiating singletons in " + this);
        }        // Iterate over a copy to allow for init methods which in turn register new bean definitions.
        // While this may not be part of the regular factory bootstrap, it does otherwise work fine.
        List<String> beanNames = new ArrayList<String>(this.beanDefinitionNames);        // Trigger initialization of all non-lazy singleton beans...
        // 触发实例化所有的非懒加载的单例
        for (String beanName : beanNames) {
           ...
        }        // Trigger post-initialization callback for all applicable beans...
        // 触发应用bean的post-initialization回调，也就是afterSingletonsInstantiated方法
        for (String beanName : beanNames) {
            Object singletonInstance = getSingleton(beanName);            if (singletonInstance instanceof SmartInitializingSingleton) {                final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;                if (System.getSecurityManager() != null) {
                    AccessController.doPrivileged(new PrivilegedAction<Object>() {                        @Override
                        public Object run() {
                            smartSingleton.afterSingletonsInstantiated();                            return null;
                        }
                    }, getAccessControlContext());
                }                else {
                    smartSingleton.afterSingletonsInstantiated();
                }
            }
        }
    }

1. SmartLifecycle.start在ApplicationContext结束刷新finishRefresh时，getLifecycleProcessor().onRefresh();

判断bean是否为SmartLifecycle并且autoStartup。

位于：
DefaultLifecycleProcessor.onRefresh

1. stop方法在Application.close的时候，调用getLifecycleProcessor().stop()方法仍然在DefaultLifecycleProcessor内部

1. DisposableBean.destroy方法，doCreateBean方法中会判断bean是否有销毁相关操作，实现了DisposableBean方法或定义了销毁方法。

AbstractAutowireCapableBeanFactory.doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)

代码演示

public class HelloWorld implements SmartInitializingSingleton,SmartLifecycle,InitializingBean,        DisposableBean,MyInterface,BeanNameAware,ApplicationContextAware{    private final Log logger = LogFactory.getLog(getClass());    private boolean isRunning;    

    public HelloWorld() {
        System.out.println("实例化");
    }    public void sayHello(){
        System.out.println("hello World");
    }    public void afterSingletonsInstantiated() {
        System.out.println("SmartInitializingSingleton afterSingletonsInstantiated");
    }    public void start() {
        isRunning = true;
        System.out.println("LifeCycle start");
    }    public void stop() {
        System.out.println("LifeCycle stop");
    }    public boolean isRunning() {        return isRunning;
    }    public boolean isAutoStartup() {        return true;
    }    public void stop(Runnable callback) {
        System.out.println("LifeScycle stop");
        callback.run();
    }    public int getPhase() {        return 0;
    }    public void afterPropertiesSet() throws Exception {
        System.out.println("afterproperties set");
    }    public void destroy() throws Exception {
        System.out.println("destroy");
    }    public void my(String str) {
        System.out.println(str);
    }    public void setBeanName(String name) {
        System.out.println("set bean Name aware");
    }    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        System.out.println("set Application Aware");
    }
}//MyInterface接口public interface MyInterface {    void my(String str);
}//app.xml<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="porcessor" class="me.aihe.MyBeanPostProcessor" />
    <bean id="hello" class="me.aihe.HelloWorld">

    </bean>
</beans>//SpringApppublic class SpringApp {    public static void main(String[] args) {
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("app.xml");
        HelloWorld hello = (HelloWorld) applicationContext.getBean("hello");
        hello.sayHello();
        applicationContext.close();
    }
}

运行结果：

最后

可对照源代码自行验证生命周期。