bean生命周期

bean生命周期

• 初始化和销毁三种方式
• • 1.指定初始化和销毁方法
  • • 代码实现（单实例bean）
    • 多实例的bean
  • 2.通过让Bean实现InitializingBean和DisposableBean
  • • 代码实现
  • 3.使用JSR250
  • • 代码实现
• 执行初始化方法前后拦截
• • BeanPostProcessor
  • 代码实现
  • 源码
  • 拓展
  • • Spring底层对 BeanPostProcessor 的使用
    • • 代码实现

bean创建-->初始化-->销毁
容器管理bean的生命周期
1.构造（对象创建）
  单实例：默认在容器启动的时候创建对象
  多实例：在每次获取对象的时候创建对象
BeanPostProcessor.postProcessBeforeInitialization（初始化之前工作）
2.初始化
  对象创建完成，并赋值好，调用初始化方法  
BeanPostProcessor.postProcessAfterInitialization（初始化之后工作）
3.销毁：
  单实例：容器关闭的时候
  多实例：容器不会管理这个bean，容器不会调用销毁方法  

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初始化和销毁三种方式

1.指定初始化和销毁方法

代码实现（单实例bean）

在配置类当中通过@Bean指定init-method和destroy-method

@ComponentScan("com.ly.springannotation.bean")
@Configuration
public class MainConfigOfLifeCycle {

    @Bean(initMethod = "init", destroyMethod = "destroy")
    public Car car() {
        return new Car();
    }
}

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/**
 * @author luoyong
 * @Description: Car
 * @create 2019-12-29 11:39
 * @last modify by [LuoYong 2019-12-29 11:39]
 **/
@Component
public class Car {
    public Car() {
        System.out.println("car...constructor...");
    }

    public void init() {
        System.out.println("car...init...");
    }

    public void destroy() {
        System.out.println("car ... destroy...");
    }
}

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测试

public class IOCTest_LifeCycle {
    @Test
    public void test01() {
        //1、创建ioc容器
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainConfigOfLifeCycle.class);
        System.out.println("容器创建完成...");
        //关闭容器的时候销毁对象
        applicationContext.close();
    }
}

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测试结果

多实例的bean

@ComponentScan(value = "com.ly.springannotation.bean",includeFilters = {@ComponentScan.Filter(type =
        FilterType.ASSIGNABLE_TYPE,classes = {Car.class})},useDefaultFilters = false)
@Configuration
public class MainConfigOfLifeCycle {

    @Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
    @Bean(initMethod = "init", destroyMethod = "destroy")
    public Car car() {
        return new Car();
    }
}

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测试代码

public class IOCTest_LifeCycle {
    @Test
    public void test01() {
        //1、创建ioc容器
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainConfigOfLifeCycle.class);
        System.out.println("容器创建完成...");
        //多实例bean在获取的时候才会创建对象
        Car car =(Car) applicationContext.getBean("car");
        //关闭容器的时候销毁对象
        applicationContext.close();
    }
}

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执行结果

多 实 例 b e a n 容 器 不 会 管 理 这 个 b e a n ， 不 会 调 用 销 毁 方 法 进 行 销 毁 color{blue}{多实例bean容器不会管理这个bean，不会调用销毁方法进行销毁}多实例bean容器不会管理这个bean，不会调用销毁方法进行销毁

2.通过让Bean实现InitializingBean和DisposableBean

I n i t i a l i z i n g B e a n ： 定 义 初 始 化 逻 辑 color{red}{InitializingBean：定义初始化逻辑}InitializingBean：定义初始化逻辑
D i s p o s a b l e B e a n ： 定 义 销 毁 逻 辑 color{blue}{DisposableBean：定义销毁逻辑}DisposableBean：定义销毁逻辑

代码实现

@ComponentScan(value = "com.ly.springannotation.bean",includeFilters = {@ComponentScan.Filter(type =
        FilterType.ASSIGNABLE_TYPE,classes = {Cat.class})},useDefaultFilters = false)
@Configuration
public class MainConfigOfLifeCycle {
}

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@Component
public class Cat implements InitializingBean, DisposableBean {
    public Cat() {
        System.out.println("Cat...constructor....");
    }

    @Override
    public void destroy() throws Exception {
        System.out.println("Cat...destroy....");
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("Cat...afterPropertiesSet....");
    }
}

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测试

public class IOCTest_LifeCycle {
    @Test
    public void test01() {
        //1、创建ioc容器
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainConfigOfLifeCycle.class);
        System.out.println("容器创建完成...");
        //关闭容器的时候销毁对象
        applicationContext.close();
    }
}

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测试结果

3.使用JSR250

@PostConstruct：在bean创建完成并且属性赋值完成；来执行初始化方法
@PreDestroy：在容器销毁bean之前通知我们进行清理工作

代码实现

@ComponentScan(value = "com.ly.springannotation.bean",includeFilters = {@ComponentScan.Filter(type =
        FilterType.ASSIGNABLE_TYPE,classes = {Dog.class})},useDefaultFilters = false)
@Configuration
public class MainConfigOfLifeCycle {
}

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@Component
public class Dog {

    public Dog() {
        System.out.println("Dog...constructor...");
    }

    //对象创建并赋值之后调用
    @PostConstruct
    public void init() {
        System.out.println("Dog...init...@PostConstruct...");
    }

    //容器移除对象之前
    @PreDestroy
    public void destroy() {
        System.out.println("Dog ... destroy...@PreDestroy...");
    }
}

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测试

public class IOCTest_LifeCycle {
    @Test
    public void test01() {
        //1、创建ioc容器
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainConfigOfLifeCycle.class);
        System.out.println("容器创建完成...");
        //关闭容器的时候销毁对象
        applicationContext.close();
    }
}

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测试结果

执行初始化方法前后拦截

BeanPostProcessor

在bean初始化前后进行一些处理工作
postProcessBeforeInitialization:在初始化之前工作
postProcessAfterInitialization:在初始化之后工作

代码实现

@ComponentScan(value = "com.ly.springannotation.bean",includeFilters = {@ComponentScan.Filter(type =
        FilterType.ASSIGNABLE_TYPE,classes = {Dog.class, MyBeanPostProcessor.class})},useDefaultFilters = false)
@Configuration
public class MainConfigOfLifeCycle {
}

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@Component
public class Dog{
    public Dog() {
        System.out.println("Dog...constructor...");
    }
    //对象创建并赋值之后调用
    @PostConstruct
    public void init() {
        System.out.println("Dog...init...@PostConstruct...");
    }
    //容器移除对象之前
    @PreDestroy
    public void destroy() {
        System.out.println("Dog ... destroy...@PreDestroy...");
    }
}
@Component
public class MyBeanPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("postProcessBeforeInitialization..." + beanName + "=>" + bean);
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("postProcessAfterInitialization..." + beanName + "=>" + bean);
        return bean;
    }
}

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测试

public class IOCTest_LifeCycle {
    @Test
    public void test01() {
        //1、创建ioc容器
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainConfigOfLifeCycle.class);
        System.out.println("容器创建完成...");
        //关闭容器的时候销毁对象
        applicationContext.close();
    }
}

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测试结果：

源码

AbstractAutowireCapableBeanFactory 553 populateBean(beanName, mbd, instanceWrapper); 对bean的属性进行赋值
AbstractAutowireCapableBeanFactory 555 exposedObject = initializeBean(beanName, exposedObject, mbd);

AbstractAutowireCapableBeanFactory 1604 初始化实现细节

	protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
		if (System.getSecurityManager() != null) {
			AccessController.doPrivileged(new PrivilegedAction<Object>() {
				@Override
				public Object run() {
					invokeAwareMethods(beanName, bean);
					return null;
				}
			}, getAccessControlContext());
		}
		else {
			invokeAwareMethods(beanName, bean);
		}

		Object wrappedBean = bean;
		if (mbd == null || !mbd.isSynthetic()) {
		    //初始化之前执行
			wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
		}

		try {
		    //执行自定义初始化方法
			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()) {
		    //初始化之后执行
			wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
		}
		return wrappedBean;
	}

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	@Override
	public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
			throws BeansException {

		Object result = existingBean;
		for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
			result = beanProcessor.postProcessBeforeInitialization(result, beanName);
			if (result == null) {
				return result;
			}
		}
		return result;
	}
		@Override
	public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
			throws BeansException {

		Object result = existingBean;
		for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
			result = beanProcessor.postProcessAfterInitialization(result, beanName);
			if (result == null) {
				return result;
			}
		}
		return result;
	}

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拓展

Spring底层对 BeanPostProcessor 的使用

bean赋值，注入其他组件，@Autowired，生命周期注解功能，@Async,xxx 都是实现 BeanPostProcessor来完成的
举例：ApplicationContextAwareProcessor bean当中注入ioc容器

代码实现

@Component
public class Dog implements ApplicationContextAware {

    private ApplicationContext applicationContext;


    public Dog() {
        System.out.println("Dog...constructor...");
    }

    //对象创建并赋值之后调用
    @PostConstruct
    public void init() {
        System.out.println("Dog...init...@PostConstruct...");
    }

    //容器移除对象之前
    @PreDestroy
    public void destroy() {
        System.out.println("Dog ... destroy...@PreDestroy...");
    }


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

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执行链路图

关键步骤：
AbstractAutowireCapableBeanFactory 1620 wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
AbstractAutowireCapableBeanFactory 409 esult = beanProcessor.postProcessBeforeInitialization(result, beanName);
ApplicationContextAwareProcessor 97 invokeAwareInterfaces(bean);
ApplicationContextAwareProcessor 121 
			if (bean instanceof ApplicationContextAware) {
				((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
			}
Dog 42
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }			
原文章：https://blog.csdn.net/ly10228/article/details/112062172