spring中bean生命周期的初始化和销毁的几种方法详解

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发布于 2021-12-23 12:28:57

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发布于 2021-12-23 12:28:57

最近在重新学习spring优秀的框架，顺便记录一下自己的总结，同时分享给大家。bean的生命周期指的是：bean创建–>初始化–>销毁的过程，bean的生命周期由容器进行管理，我们可以自定义bean的初始化和销毁方法来满足我们的需求，当容器在bean进行到当前生命周期的时候，来调用自定义的初始化和销毁方法。今天主要讲解如何定义初始化和销毁的4中方法。

1，使用initMethod和destroyMethod

下面代码全部是通过配置类，而不是配置xml文件

Train.java

package cap5.bean;

public class Train {

	public Train() {
		// TODO Auto-generated constructor stub
		super();
		System.out.println("Train创建");
	}
	
	public void init() {
		System.out.println("train init...");
	}
	
	public void destroy() {
		System.out.println("train destroy");
	}
}

MainConfig.java

package cap5.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.FilterType;
import org.springframework.context.annotation.ComponentScan.Filter;

import cap5.bean.Bike;
import cap5.bean.Jeep;
import cap5.bean.TaolongBeanPostProcessor;
import cap5.bean.Train;
//@ComponentScan(value= {"cap5.bean"},includeFilters= {@Filter(type=FilterType.ASSIGNABLE_TYPE,classes=TaolongBeanPostProcessor.class)})
@Configuration
public class MainConfig {

	@Bean(initMethod="init",destroyMethod="destroy")
	public Train train() {
		return new Train();
	}
	
	/*@Bean
	public Bike bike() {
		return new Bike();
	}*/
	
	/*@Bean
	public Jeep jeep() {
		return new Jeep();
	}*/
}

MainTest.java

package cap5.test;

import org.junit.Test;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import cap5.config.MainConfig;

public class MainTest {

	@Test
	public void test() {
		AnnotationConfigApplicationContext app = new AnnotationConfigApplicationContext(MainConfig.class);
		
		System.out.println("IOC 容器创建完成");
		System.out.println("IOC 容易准备关闭");
		/*String[] names = app.getBeanDefinitionNames();
		for(String name:names) {
			System.out.println("name="+name);
		}*/
		app.close();
		
	}
}

打印结果：

2，让bean实现InitializingBean和DisposableBean接口，然后分别实现afterPropertiesSet（）方法和destroy（）方法

afterPropertiesSet()：从名字上就能看出，这个其实不是bean真正的初始化方法，而是在bean构建完成，设置好了属性之后调用的方法—–作用相当于初始化方法

destroy()：当bean销毁时,会把单实例bean进行销毁

Bike.java

package cap5.bean;

import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;

public class Bike implements InitializingBean,DisposableBean{

	public Bike() {
		// TODO Auto-generated constructor stub
		super();
		System.out.println("bike construct...");
	}
	public void destroy() throws Exception {
		// TODO Auto-generated method stub
		System.out.println("bike destroy");
	}

	public void afterPropertiesSet() throws Exception {
		// TODO Auto-generated method stub
		System.out.println("bike init...");
		
	}

}

MainConfig.java

package cap5.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.FilterType;
import org.springframework.context.annotation.ComponentScan.Filter;

import cap5.bean.Bike;
import cap5.bean.Jeep;
import cap5.bean.TaolongBeanPostProcessor;
import cap5.bean.Train;
//@ComponentScan(value= {"cap5.bean"},includeFilters= {@Filter(type=FilterType.ASSIGNABLE_TYPE,classes=TaolongBeanPostProcessor.class)})
@Configuration
public class MainConfig {

	/*@Bean(initMethod="init",destroyMethod="destroy")
	public Train train() {
		return new Train();
	}*/
	
	@Bean
	public Bike bike() {
		return new Bike();
	}
	
	/*@Bean
	public Jeep jeep() {
		return new Jeep();
	}*/
}

MainTest.java和上面的一样，就不再贴上来了

测试结果：

3，使用JSR250规则定义的注解来实现，JSR250的详细了解可自行百度，主要使用如下两个注解

@PostConstruct：从名字上也能看出这个注解的意思，就是在bean构建完成之后调用—相当于初始化

@PreDestroy：从名字上也能看出是在beandestroy之前会执行的被注解的方法—相当于销毁

Jeep.java

package cap5.bean;
import javax.annotation.*;

public class Jeep {

	public Jeep() {
		// TODO Auto-generated constructor stub
		super();
		System.out.println("jeep construct...");
	}
	
	@PostConstruct
	public void init() {
		System.out.println("jeep init...");
	}
	
	@PreDestroy
	public void destroy() {
		System.out.println("jeep destroy...");
	}
}

MainConfig.java

package cap5.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.FilterType;
import org.springframework.context.annotation.ComponentScan.Filter;

import cap5.bean.Bike;
import cap5.bean.Jeep;
import cap5.bean.TaolongBeanPostProcessor;
import cap5.bean.Train;
//@ComponentScan(value= {"cap5.bean"},includeFilters= {@Filter(type=FilterType.ASSIGNABLE_TYPE,classes=TaolongBeanPostProcessor.class)})
@Configuration
public class MainConfig {

	/*@Bean(initMethod="init",destroyMethod="destroy")
	public Train train() {
		return new Train();
	}*/
	
	/*@Bean
	public Bike bike() {
		return new Bike();
	}*/
	
	@Bean
	public Jeep jeep() {
		return new Jeep();
	}
}

MainTest.java和上面一样，不重新贴了

运行结果：

4，第四种方法是使用后置处理器，在bean初始化前后时会调用实现了BeanPostProcessor接口并重写两个方法，分别是：postProcessBeforeInitialization()和postProcessAfterInitialization()方法

TaolongBeanPostProcessor.java

package cap5.bean;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;
@Component
public class TaolongBeanPostProcessor implements BeanPostProcessor {


	public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		// TODO Auto-generated method stub
		System.out.println("bean-----"+beanName+" init start...");
		return bean;
	}
	

	public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
		// TODO Auto-generated method stub
		
		System.out.println("bean------"+beanName+" init end...");
		return bean;
	}
}

Plane.java

package cap5.bean;

public class Plane {

	public Plane() {
		// TODO Auto-generated constructor stub
		System.out.println("plane construct...");
	}
	
}

MainConfig.java

package cap5.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.FilterType;
import org.springframework.context.annotation.ComponentScan.Filter;

import cap5.bean.Bike;
import cap5.bean.Jeep;
import cap5.bean.Plane;
import cap5.bean.TaolongBeanPostProcessor;
import cap5.bean.Train;
//@ComponentScan(value= {"cap5.bean"},includeFilters= {@Filter(type=FilterType.ASSIGNABLE_TYPE,classes=TaolongBeanPostProcessor.class)})
@Configuration
public class MainConfig {

	/*@Bean(initMethod="init",destroyMethod="destroy")
	public Train train() {
		return new Train();
	}*/
	
	/*@Bean
	public Bike bike() {
		return new Bike();
	}*/
	
	/*@Bean
	public Jeep jeep() {
		return new Jeep();
	}*/
	@Bean
	public Plane plane() {
		return new Plane();
	}
	
	@Bean
	public TaolongBeanPostProcessor taolongBeanPostProcessor() {
		return new TaolongBeanPostProcessor();
	}
}

测试效果：

上面都是默认情况下的单例的bean模式，加入在多个bean的情况下呢？容器如何管理bean的生命周期呢？

（1）当bean是多实例的模式下，bean不会在IOC容器创建的时候，去实例化bean，而是在真正使用该bean的时候实例化，这一点可以进行简单的测试一下，当增加@scope（”protorype“）时，就是多实例创建bean了

（2）当容器关闭的时候，多实例的情况下怎么处理，会不会将多个实例同时销毁呢？

我们来简单的测试一下：

MainConfig.java部分代码

@Scope("prototype")
	@Bean
	public Bike bike() {
		return new Bike();
	}

MianTest.java

package cap5.test;

import org.junit.Test;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import cap5.bean.Bike;
import cap5.config.MainConfig;

public class MainTest {

	@Test
	public void test() {
		AnnotationConfigApplicationContext app = new AnnotationConfigApplicationContext(MainConfig.class);
		System.out.println("IOC 容器创建完成");
		Bike bike1 = (Bike)app.getBean(Bike.class);
		Bike bike2 = (Bike)app.getBean(Bike.class);
		System.out.println(bike1==bike2);
		System.out.println("IOC 容易准备关闭");
		/*String[] names = app.getBeanDefinitionNames();
		for(String name:names) {
			System.out.println("name="+name);
		}*/
		app.close();
		
	}
}

运行结果：