1 Spring Bean 销毁阶段划分
- Bean 销毁前阶段
- Bean 销毁阶段
- Bean 垃圾回收（GC）
2 Spring Bean 销毁各阶段详细分析
2.1 Bean 销毁前阶段
DestructionAwareBeanPostProcessor#postProcessBeforeDestruction
2.1.1 代码示例
...
public class MyDestructionAwareBeanPostProcessor implements DestructionAwareBeanPostProcessor{
@Override
public void postProcessBeforeDestruction(Object bean, String beanName) throws BeansException {
if (ObjectUtils.nullSafeEquals("userHolder", beanName) && UserHolder.class.equals(bean.getClass()))
}
}
2.1.2 源码讲解
public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport implements ConfigurableBeanFactory {
...
@Override
public void destroyBean(String beanName, Object beanInstance) {
destroyBean(beanName, beanInstance, getMergedLocalBeanDefinition(beanName));
}
...
protected void destroyBean(String beanName, Object bean, RootBeanDefinition mbd) {
new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), getAccessControlContext()).destroy();
}
...
}
class DisposableBeanAdapter implements DisposableBean, Runnable, Serializable {
...
@Override
public void destroy() {
if (!CollectionUtils.isEmpty(this.beanPostProcessors)) {
for (DestructionAwareBeanPostProcessor processor : this.beanPostProcessors) {
processor.postProcessBeforeDestruction(this.bean, this.beanName);
}
}
...
}
...
}
2.2 Bean 销毁阶段
- @PreDestroy 标准方法
- 实现 DisposableBean 接口的 destroy() 方法
- 自定义销毁方法
2.2.1 代码示例
<?xml version="1.0" encoding="UTF-8"?>
<beans
xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
https://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
https://www.springframework.org/schema/beans/spring-context.xsd">
<bean class="org.wmg.thinking.in.spring.bean.lifecycle.MyInstantiationAwareBeanPostProcessor" />
<bean id = "userHolder" class="org.wmg.thinking.in.spring.bean.lifecycle.UserHolder" autowire="constructor" destroy-method="doDestroy">
<!-- 通过 XML 元素配置 -->
<property name="description" value="the user holder" />
</bean>
</beans>
public class UserHolder implements DisposableBean {
...
@PreDestroy
public void preDestroy() {
// postProcessBeforeDestruction() = the user holder v9
this.description = "the user holder v10";
System.out.println("preDestroy() = " + description);
}
@Override
public void destroy() throws Exception {
// preDestroy() = "the user holder v11";
this.description = "the user holder v11";
System.out.println("destroy() = " + description);
}
public void doDestroy(){
// destroy = "the user holder v12";
this.description = "the user holder v12";
System.out.println("doDestroy() = " + description);
}
...
}
2.2.2 源码讲解
public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport implements ConfigurableBeanFactory {
...
@Override
public void destroyBean(String beanName, Object beanInstance) {
destroyBean(beanName, beanInstance, getMergedLocalBeanDefinition(beanName));
}
...
protected void destroyBean(String beanName, Object bean, RootBeanDefinition mbd) {
new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), getAccessControlContext()).destroy();
}
...
}
class DisposableBeanAdapter implements DisposableBean, Runnable, Serializable {
...
@Override
public void destroy() {
...
if (this.destroyMethod != null) {
invokeCustomDestroyMethod(this.destroyMethod);
}
...
}
...
}
2.3 Bean 垃圾回收（GC）
- 关闭 Spring 容器（应用上下文）
- 执行 GC
- Spring Bean 覆盖 finalize() 方法被回调
2.3.1 代码示例
public class UserHolder implements BeanNameAware, BeanClassLoaderAware, BeanFactoryAware, EnvironmentAware,
InitializingBean, SmartInitializingSingleton, DisposableBean {
...
protected void finalize() throws Throwable {
System.out.println("UserHolder is finalzied...");
}
}
public class BeanLifecycleDemo {
public static void main(String[] args) throws InterruptedException {
DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
beanFactory.addBeanPostProcessor(new MyInstantiationAwareBeanPostProcessor());
// 添加 MyDestructionAwareBeanPostProcessor 执行销毁前回调
beanFactory.addBeanPostProcessor(new MyDestructionAwareBeanPostProcessor());
// 添加 CommonAnnotationBeanPostProcessor 解决 @PostConstructor
beanFactory.addBeanPostProcessor(new CommonAnnotationBeanPostProcessor());
// 基于 XML 资源 BeanDefinitionReader 实现
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
String[] locations = {"META-INF/dependency-lookup-context.xml",
"META-INF/bean-constructor-dependency-injection.xml"};
int beanNumbers = beanDefinitionReader.loadBeanDefinitions(locations);
System.out.println("已加载 BeanDefinition 数量：" + beanNumbers);
// 显示执行 preInstantiateSingletons()
// SmartInitliziingSingleton 通常在 Spring ApplicationContext 场景使用。
// preInstantiateSingletons() 将已注册的 BeanDefinition 初始化成 Spring Bean
beanFactory.preInstantiateSingletons();
// 通过 Bean id 和类型进行依赖查找
User user = beanFactory.getBean("user", User.class);
System.out.println(user);
User superUser = beanFactory.getBean("superUser", User.class);
System.out.println(superUser);
// 构造器注入按照类型注入，resolveDependency
UserHolder userHolder = beanFactory.getBean("userHolder", UserHolder.class);
System.out.println(userHolder);
//执行 Bean 销毁（容器内）
beanFactory.destroyBean("userHolder", userHolder);
// Bean 销毁并不意味着 Bean 垃圾回收了
System.out.println(userHolder);
// 销毁 BeanFactory 中的单例 Bean
beanFactory.destroySingletons();;
//强制 GC
System.gc();
// 等待一段时间
Thread.sleep(1000L);
//强制 GC
System.gc();
}
}
