bean装载到Spring应用上下文的生命周期

在基于Spring的应用中，应用对象生存于Spring容器中，Spring容器负责创建对象，装配对象，配置对象，并管理对象的整个生命周期，从生存到死亡。

bean装载到Spring应用上下文中的生命周期过程如图所示：

过程解释：
1. Spring对bean进行实例化；

2. Spring将值和bean的引用注入到bean对应的属性中；

3. 如果bean实现了BeanNameAware接口，Spring将bean的ID传递给setBeanName()方法；

4. 如果bean实现了BeanFactoryAware接口，Spring将调用setBeanFactory()方法，将BeanFactory容器实例传入；

5. 如果bean实现了ApplicationContextAware接口，Spring将调用setApplicationContext()方法，将bean所在的应用上下文的引用传入进来；

6. 如果bean实现了BeanPostProcessor接口，Spring将调用它们的postProcessBeforeIniitialization()方法；

7. 如果bean实现了InitializingBean接口，Spring将调用它们的afterPropertiesSet()方法。

8. 如果bean使用initMethod声明了初始化方法，该方法也会被调用；

9. 如果bean实现了BeanPostProcessor接口，Spring将调用的postProcessAfterInitialization()方法；

10. 此时，bean已经准备就绪，可以被应用程序使用了，它们将一直驻留在应用上下文中，直到该应用上下文被销毁；

11. 如果bean实现了DisposableBean接口，Spring将调用它的destroy()接口方法。

12. 如果bean使用destroy-method声明了销毁方法，该方法也会被调用。

测试代码：

package beanlifecycle;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.*;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;

/**
 * bean的定义
 */
public class MySpringBeanLifeCycle implements
        BeanNameAware,
        BeanFactoryAware,
        ApplicationContextAware,
        InitializingBean,
        DisposableBean {

    private ApplicationContext applicationContext;

    public MySpringBeanLifeCycle() {
        System.out.println("实例化 MySpringBeanLifeCycle ...");
    }

    @Override
    public void setBeanName(String s) {
        System.out.println("BeanNameAware -> setBeanName ...");
    }

    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        System.out.println("BeanFactoryAware --> setBeanFactory ...");
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        System.out.println("ApplicationContextAware -> setApplicationContext ...");
    }

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

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

    public void customInit() {
        System.out.println("自定义初始化方法...");
    }

    public void customDestroy() {
        System.out.println("自定义销毁方法...");
    }
}

package beanlifecycle;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;

/**
 * 实现BeanPostProcessor接口
 */
public class MySpringBeanPostProcessor implements BeanPostProcessor {

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if (bean instanceof MySpringBeanLifeCycle) {
            System.out.println("BeanPostProcessor -> postProcessBeforeInitialization ...");
        }
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if (bean instanceof MySpringBeanLifeCycle) {
            System.out.println("BeanPostProcessor -> postProcessAfterInitialization ...");
        }
        return bean;
    }
}

package beanlifecycle;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * bean配置类
 */
@Configuration
public class BeanLifeCycleConfig {

    @Bean(initMethod = "customInit", destroyMethod = "customDestroy")
    public MySpringBeanLifeCycle mySpringBeanLifeCycle() {
        return new MySpringBeanLifeCycle();
    }

    @Bean
    public MySpringBeanPostProcessor mySpringBeanPostProcessor() {
        return new MySpringBeanPostProcessor();
    }
}

package beanlifecycle;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class Main {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(BeanLifeCycleConfig.class);
        context.getBean(MySpringBeanLifeCycle.class);
        context.destroy();
    }
}

运行结果

实例化 MySpringBeanLifeCycle ...
BeanNameAware -> setBeanName ...
BeanFactoryAware --> setBeanFactory ...
ApplicationContextAware -> setApplicationContext ...
BeanPostProcessor -> postProcessBeforeInitialization ...
InitializingBean -> afterPropertiesSet ...
自定义初始化方法...
BeanPostProcessor -> postProcessAfterInitialization ...
DisposableBean -> destroy...
自定义销毁方法...

参考《Spring实战（第4版）》