springIOC的一些扩展点解读

Spring扩展点

1、SpringIOC扩展点

1.1、bean的生命周期

• BeanNameAware's {@code setBeanName}

• BeanClassLoaderAware's {@code setBeanClassLoader}

• BeanFactoryAware's {@code setBeanFactory}

• EnvironmentAware's {@code setEnvironment}

• EmbeddedValueResolverAware's {@code setEmbeddedValueResolver}

• ResourceLoaderAware's {@code setResourceLoader}

============ 应用程序上下文运行时可用================ start

• ApplicationEventPublisherAware's {@code setApplicationEventPublisher}
• MessageSourceAware's {@code setMessageSource}
• ApplicationContextAware's {@code setApplicationContext}

============ 应用程序上下文运行时可用================ end
============ web应用程序上下文运行时可用================ start

• ServletContextAware's {@code setServletContext}

============ web应用程序上下文运行时可用================ end

============ 初始化阶段============================================

• {@code postProcessBeforeInitialization} methods of BeanPostProcessors
• InitializingBean's {@code afterPropertiesSet}
• a custom init-method definition
• {@code postProcessAfterInitialization} methods of BeanPostProcessors

============ 销毁阶段============================================

• {@code postProcessBeforeDestruction} methods of DestructionAwareBeanPostProcessors
• DisposableBean's {@code destroy}
• a custom destroy-method definition

解释下xxxAware 我们看到bean的生命周期是先加载了一堆的Aware结尾的类。Aware意思为具有xxx的能力，假如你实现了该类型接口，你的类就具有了Aware前面描述的能力，例如

我实现了EnvironmentAware 我的当前类就拥有了Environment的能力。

public class CustomEnvironment implements EnvironmentAware{
	private static Environment environment;

	@Override
    public void setEnvironment(Environment environment) {
        CustomEnvironment.environment = environment;
    }
}

这些类的作用就是让你在做扩展的时候能够很方便直接使用IOC容器的一系列能力。

执行完Aware之后接下来就是初始化阶段执行实现了BeanPostProcessors接口的postProcessBeforeInitialization方法，然后再执行InitializingBean的afterPropertiesSet方法初始化，然后执行自定义初始化方法，然后再执行BeanPostProcessors的postProcessAfterInitialization方法。销毁阶段先执行DestructionAwareBeanPostProcessor的postProcessBeforeDestruction方法销毁需要回收的bean实例，如listener实例。接着执行DisposableBean接口的destroy方法，最后执行自定义的销毁方法。

简单的验证例子

定义一个CustomBeanPostProcessor

/**
 * @Description TODO
 * @Author 姚仲杰#80998699
 * @Date 2021/3/16 14:27
 */
@Component
public class CustomBeanPostProcessor implements BeanPostProcessor {
    
    
    
    @Bean(initMethod = "customInit",destroyMethod = "customDestroy")
    TestBean testBean(){
    
    
        return new TestBean();
    }
    
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName)
        throws BeansException {
    
    
        if (bean instanceof TestBean) {
    
    
            System.out.println("2、BeanPostProcessor:postProcessBeforeInitialization");
        }
        return bean;
    }
    
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName)
        throws BeansException {
    
    
        if (bean instanceof TestBean) {
    
    
            System.out.println("5、BeanPostProcessor:postProcessAfterInitialization");
        }
        return bean;
    }

在定义一个TestBean，并在CustomBeanPostProcessor使用@Bean注解初始化设置自定义初始化以及销毁方法。按我们所知道的顺序给他们标上序号。

/**
 * @Description TODO
 * @Author 姚仲杰#80998699
 * @Date 2021/3/16 14:38
 */
public class TestBean implements InitializingBean, DisposableBean, ApplicationContextAware {
    
    
    
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
    
    
        System.out.println("1、setApplicationContext");
    }
    
    @Override
    public void afterPropertiesSet() throws Exception {
    
    
        System.out.println("3、InitializingBean:afterPropertiesSet");
    }
    /**
     * 自定义初始化
     */
    public void customInit() {
    
    
        System.out.println("4、TestBean：custom init");
    }
    
    @Override
    public void destroy() throws Exception {
    
    
        System.out.println("6、DisposableBean:destroy");
    }
    /**
     * 自定义销毁
     */
    public void customDestroy() {
    
    
        System.out.println("7、TestBean：custom destroy");
    }
    
}

然后直接运行输出结果如下。

1、setApplicationContext
2、BeanPostProcessor:postProcessBeforeInitialization
3、InitializingBean:afterPropertiesSet
4、TestBean：custom init
5、BeanPostProcessor:postProcessAfterInitialization
停止时打印如下信息
6、DisposableBean:destroy
7、TestBean：custom destroy

小提示：不要把@PostConstruct 与@PreDestroy当作自定义初始化和销毁的注解。他们不是。这两个注解执行时机时在InitializingBean:afterPropertiesSet之前和DisposableBean:destroy之前。