Bean 何时被 GC

た入场券 2022-11-03 00:58 185阅读 0赞

当一个对象要被 JVM 垃圾收集器回收掉时会执行对象的 finalize 方法，所以 User 类对该方法进行重写

package constxiong;
    
    public class User {
    
    	@Override
    	protected void finalize() throws Throwable {
    		System.out.printf("我(id:%d)要被 gc 回收了
    ", id);
    		super.finalize();
    	}
    
    	private Integer id;
    
    	private String name;
    
    	public User(Integer id) {
    		this.id = id;
    		System.out.println("init id:" + id);
    	}
    
    	public void setId(Integer id) {
    		this.id = id;
    	}
    
    	public String getName() {
    		return name;
    	}
    
    	public void setName(String name) {
    		this.name = name;
    	}
    
    	@Override
    	public String toString() {
    		return "User{" +
    				"id=" + id +
    				", name='" + name + ''' +
    				"}";
    	}
    }

在 spring xml 配置文件里配两个 bean：user1、user2

测试类

/**
     * 测试 Bean gc
     * @author ConstXiong
     */
    public class Test {
    	
    	public static void main(String[] args) throws InterruptedException {
    		ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("META-INF/spring-bean-gc.xml");
    		//刷新 ioc 容器
    		context.refresh();
    		System.out.println(context.getBean("user1", User.class));
    		BeanDefinitionRegistry registry = (DefaultListableBeanFactory)context.getBeanFactory();
    		registry.removeBeanDefinition("user1");
    		Thread.sleep(3000L);
    		//关闭 ioc 容器
    		context.close();
    		System.out.println("ioc 容器关闭");
    		System.gc();
    		Thread.sleep(3000L);
    	}
    }

打印结果

init id:1
    init id:2
    init id:1
    init id:2
    User{id=1, name='constxiong'}
    ioc 容器关闭
    我(id:1)要被 gc 回收了
    我(id:2)要被 gc 回收了
    我(id:1)要被 gc 回收了
    我(id:2)要被 gc 回收了

看到以上情况可能会比较惊讶，说明一下：

*  如果不调用 context 的 refresh() 和 close() 方法是看不到 GC 效果的，即 main 方法里的所有对象的内存都随着进程关闭直接被释放了
 *  调用 context 的 refresh() 方法，会发现 user1 和 user2 会再次被实例化，进行注册
 *  调用注册中心的 removeBeanDefinition() 不会导致 bean 对象被 gc 掉
 *  调用 context 的 close() 方法，在 new ClassPathXmlApplicationContext("META-INF/spring-bean-gc.xml") 实例化的 user1、user2 和 context.refresh() 方法实例化的 user1、user2，共四个对象，在 System.gc() 之后，被 gc 掉，执行了对象的 finalize 方法

[完整代码：011-spring-bean-gc][011-spring-bean-gc]

--------------------

### 【Java学习资源】整理推荐 ###

*  [自定义 Bean 作用域][Bean]
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 *  [Spring 依赖注入与依赖查找来源的区别][Spring]
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 *  [ObjectFactory 与 BeanFactory 的区别][ObjectFactory _ BeanFactory]
 *  [Bean 销毁的方式与顺序][Bean 2]
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 *  [BeanFactory 与 FactoryBean 的区别][BeanFactory _ FactoryBean]
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 *  [Spring IoC 依赖注入(支持哪些数据类型？)][Spring IoC 2]
 *  [Spring bean 依赖查找][Spring bean]
 *  [Spring-IoC][]
 *  [Spring 的核心特性][Spring 1]

--------------------

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[011-spring-bean-gc]: https://github.com/ConstXiong/toy/tree/master/spring-study/011-spring-bean-gc
[Bean]: https://www.javanav.com/val/3fdc7ac3bd034a5ab7040e23f37153fa.html
[Bean 1]: https://www.javanav.com/val/59101a7207864f4aa971e5c48b592c77.html
[maven _ tomcat _ jar _ web]: https://www.javanav.com/val/b1f4691bd6ba488a80e3bdfcefdec33c.html
[Spring]: https://www.javanav.com/val/a9569837e1bc4df9aeac0e6cbf96bf06.html
[Spring _ DependencyDescriptor]: https://www.javanav.com/val/152161d266a94fd38efb365a78d8f9a3.html
[Spring _ Aware]: https://www.javanav.com/val/089b3993c8bc4dec891ea677c104c5e4.html
[Spring Bean _ Exception]: https://www.javanav.com/val/2b31b7061b3342c0a67f8d7fc7373ed3.html
[Spring _ Bean]: https://www.javanav.com/val/92f9e0951b19454196b645bb3cb1a0b9.html
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[Bean _ GC]: https://www.javanav.com/val/ca4a8f696ee5440bb5d87d3397b59004.html
[Spring Bean 2]: https://www.javanav.com/val/b197550be7ba4bd8b4d82f6835d1abb1.html
[ObjectFactory _ BeanFactory]: https://www.javanav.com/val/016d62d99b0148feaf13529a841f4e46.html
[Bean 2]: https://www.javanav.com/val/a5a7f97894f9499b90e27dbd98124a1c.html
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[Bean 5]: https://www.javanav.com/val/a5f8bf440848487bb0c0bdaa6c846cc6.html
[BeanDefinition]: https://www.javanav.com/val/e82279480ec24184bcaf723a50ef08b3.html
[Spring IoC]: https://www.javanav.com/val/d382c8380fc2480788a35a7e671b5e9b.html
[BeanFactory _ FactoryBean]: https://www.javanav.com/val/173e873a2c98499a8a08a13b4f88ae10.html
[BeanFactory _ ApplicationContext]: https://www.javanav.com/val/bbc2c9580b7045e583855925d5f1a50b.html
[Spring IoC 1]: https://www.javanav.com/val/a835e6c709ea439ebb21a80f1bf77926.html
[Spring IoC 2]: https://www.javanav.com/val/e377beac22644c2c85308079b239a0fd.html
[Spring bean]: https://www.javanav.com/val/7f8c2e1f24db46e79bc4b9b04f9ad715.html
[Spring-IoC]: https://www.javanav.com/val/a412668efda74412a13f6df9a6d2c714.html
[Spring 1]: https://www.javanav.com/val/6eac12a548ea40c68ff64b1af307563a.html
[Link 1]: https://www.javanav.com/interview/93b0069472fd479393006c0e73043fc4.html
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[Link 10]: https://www.javanav.com/interview/67a50996c28f418e83b109ea42fc3eff.html
[Linux]: https://www.javanav.com/interview/00cccb81729540d1923bd0a0ef49533a.html
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