Spring Bean生命周期

一.概述

在spring bean生命周期中，涉及初始化和销毁​​回调。在bean生命周期中也会调用不同的spring bean感知类。一旦依赖注入完成，就会执行初始化回调方法。它们的目的是检查已在bean属性中设置的值，执行任何自定义初始化或在原始bean上提供包装等。一旦初始化回调完成，就可以使用bean了。当IoC容器即将删除bean时，执行销毁回调方法。它们的目的是释放bean持有的资源或执行任何其他完成任务。当bean实现了多个初始化和析构回调方法时，那些方法按特定顺序执行。我们将讨论初始化和销毁​​回调以及spring bean感知类的执行顺序。

二.bean生命周期步骤

bean生命周期包括以下步骤：
1.在IoC容器中，使用类构造函数创建一个spring bean。
2.使用setter方法执行依赖注入。
3.一旦依赖注入完成，BeanNameAware.setBeanName()就会被调用。在bean工厂中设置名称。
4.调用BeanClassLoaderAware.setBeanClassLoader（）提供bean实例。
5.调用BeanFactoryAware.setBeanFactory（）为bean实例提供工厂。
6.IoC容器调用BeanPostProcessor.postProcessBeforeInitialization。
7.在@PostConstruct调用带注释的方法。
8.调用@PostConstruct，InitializingBean.afterPropertiesSet()方法。
9.在init-method中调用XML配置信息找到bean中的属性。
10.调用BeanPostProcessor.postProcessAfterInitialization()
11.完成bean实例。
12.当ApplicationContext关闭时，调用registerShutdownHook()。
13.调用DisposableBean.destroy()。
14。在destroy-method调用XML配置中bean 的属性指定的方法。
15.在垃圾收集之前，调用finalize()。

三.示例

1.创建Book实体

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanClassLoaderAware;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.BeanNameAware;
import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;

public class Book implements InitializingBean, DisposableBean,
		BeanFactoryAware, BeanNameAware, BeanClassLoaderAware {
	private String bookName;

	private Book() {
		System.out.println("---inside constructor---");
	}

	@Override
	public void setBeanClassLoader(ClassLoader classLoader) {
		System.out.println("---BeanClassLoaderAware.setBeanClassLoader---");
	}

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

	public void myPostConstruct() {
		System.out.println("---init-method---");
	}

	@PostConstruct
	public void springPostConstruct() {
		System.out.println("[email protected]");
	}

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

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

	public String getBookName() {
		return bookName;
	}

	public void setBookName(String bookName) {
		this.bookName = bookName;
		System.out.println("setBookName: Book name has set.");
	}

	public void myPreDestroy() {
		System.out.println("---destroy-method---");
	}

	@PreDestroy
	public void springPreDestroy() {
		System.out.println("[email protected]");
	}

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

	@Override
	protected void finalize() {
		System.out.println("---inside finalize---");
	}
}

2.

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
public class MyBeanPostProcessor implements BeanPostProcessor {
	@Override
	public Object postProcessAfterInitialization(Object bean, String beanName)
			throws BeansException {
		System.out.println("BeanPostProcessor.postProcessAfterInitialization");
		return bean;
	}
	@Override
	public Object postProcessBeforeInitialization(Object bean, String beanName)
			throws BeansException {
		System.out.println("BeanPostProcessor.postProcessBeforeInitialization");
		return bean;
	}
} 

3.创建main

import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class SpringDemo {
	public static void main(String[] args) {
		AbstractApplicationContext context = new ClassPathXmlApplicationContext("application-config.xml");
		Book book = (Book)context.getBean("book");
		System.out.println("Book Name:"+ book.getBookName());
	        context.registerShutdownHook();
	}
} 

4.配置bean

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">
	<context:component-scan base-package="com.example.demo" />
	<bean id="book" class="com.example.demo.Book" init-method="myPostConstruct"
		destroy-method="myPreDestroy">
		<property name="bookName" value="Mahabharat" />
	</bean>
	<bean class="com.example.demo.MyBeanPostProcessor" />
</beans> 

5.运行结果

---inside constructor---
setBookName: Book name has set.
---BeanNameAware.setBeanName---
---BeanClassLoaderAware.setBeanClassLoader---
---BeanFactoryAware.setBeanFactory---
BeanPostProcessor.postProcessBeforeInitialization
[email protected]
---InitializingBean.afterPropertiesSet---
---init-method---
BeanPostProcessor.postProcessAfterInitialization
Book Name:Mahabharat
[email protected]
---DisposableBean.destroy---
---destroy-method---