Spring Bean 实例化-初始化-销毁

2020-12-23

01 实例化Spring Bean

常规

构造器（xml,java注解 Java API）
静态工厂方法(xml java api)
通过Bean工厂方法(xml java api)

通过FactoryBean（xml,java注解 Java API）

<beans xmlns="http://www.springframework.org/schema/beans"
       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">

   <!-- 静态方法实例化 Bean -->
   <bean id="user-by-static-method" class="org.geekbang.thinking.in.spring.ioc.overview.domain.User"
          factory-method="createUser"/>
   <!-- 实例（Bean）方法实例化 Bean -->
   <bean id="user-by-instance-method" factory-bean="userFactory" factory-method="createUser"/>
   <bean id="userFactory" class="org.geekbang.thinking.in.spring.bean.factory.DefaultUserFactory"/>
   <!-- FactoryBean实例化 Bean -->
   <bean id="user-by-factory-bean" class="org.geekbang.thinking.in.spring.bean.factory.UserFactoryBean" />
</beans>

特殊

ServiceLoaderFactoryBean(xml,java注解 Java API）
AutowireCapableBeanFactory#createBean(class,int,boolean)

BeanDefinitionRegistry#registerBeanDefinitoin(string,BeanDefiniton)

public class SpecialBeanInstantiationDemo {
  public static void main(String[] args) {
      // 配置 XML 配置文件
      // 启动 Spring 应用上下文
      ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:/META-INF/special-bean-instantiation-context.xml");
      // 通过 ApplicationContext 获取 AutowireCapableBeanFactory
      AutowireCapableBeanFactory beanFactory = applicationContext.getAutowireCapableBeanFactory();
      ServiceLoader<UserFactory> serviceLoader = beanFactory.getBean("userFactoryServiceLoader", ServiceLoader.class);
      displayServiceLoader(serviceLoader);
      demoServiceLoader();
      // 创建 UserFactory 对象，通过 AutowireCapableBeanFactory
      UserFactory userFactory = beanFactory.createBean(DefaultUserFactory.class);
      System.out.println(userFactory.createUser());
  }

  public static void demoServiceLoader() {
      ServiceLoader<UserFactory> serviceLoader = load(UserFactory.class, Thread.currentThread().getContextClassLoader());
      displayServiceLoader(serviceLoader);
  }

  private static void displayServiceLoader(ServiceLoader<UserFactory> serviceLoader) {
      Iterator<UserFactory> iterator = serviceLoader.iterator();
      while (iterator.hasNext()) {
          UserFactory userFactory = iterator.next();
          System.out.println(userFactory.createUser());
      }
  }
}

这里涉及到关于ServiceLoader的使用方法，想想mysql的驱动jar包是怎么被读取到项目中的，mysql定义了一系列的接口，各个厂商实现的不同的驱动都是通过ServiceLoader方式来读取的。

02 初始化Spring Bean

@PostConstruct
实现InitializingBean接口的afterPropertiesSet()方法

自定义初始化方法

xml<bean init-method=”init” ../>
Java注解 @Bean(initMethod=”init”)

Java API AbstractBeanDefinition#setInitMethodName(string)

public class DefaultUserFactory implements UserFactory, InitializingBean, DisposableBean {

  // 1. 基于 @PostConstruct 注解
  @PostConstruct
  public void init() {
      System.out.println("@PostConstruct : UserFactory 初始化中...");
  }

  public void initUserFactory() {
      System.out.println("自定义初始化方法 initUserFactory() : UserFactory 初始化中...");
  }

  @Override
  public void afterPropertiesSet() throws Exception {
      System.out.println("InitializingBean#afterPropertiesSet() : UserFactory 初始化中...");
  }

  @PreDestroy
  public void preDestroy() {
      System.out.println("@PreDestroy : UserFactory 销毁中...");
  }

  @Override
  public void destroy() throws Exception {
      System.out.println("DisposableBean#destroy() : UserFactory 销毁中...");
  }

  public void doDestroy() {
      System.out.println("自定义销毁方法 doDestroy() : UserFactory 销毁中...");
  }

  @Override
  public void finalize() throws Throwable {
      System.out.println("当前 DefaultUserFactory 对象正在被垃圾回收...");
  }
}

测试类

@Configuration // Configuration Class
public class BeanInitializationDemo {

  public static void main(String[] args) {
      // 创建 BeanFactory 容器
      AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
      // 注册 Configuration Class（配置类）
      applicationContext.register(BeanInitializationDemo.class);
      // 启动 Spring 应用上下文
      applicationContext.refresh();
      // 非延迟初始化在 Spring 应用上下文启动完成后，被初始化
      System.out.println("Spring 应用上下文已启动...");
      // 依赖查找 UserFactory
      UserFactory userFactory = applicationContext.getBean(UserFactory.class);
      System.out.println(userFactory);
      System.out.println("Spring 应用上下文准备关闭...");
      // 关闭 Spring 应用上下文
      applicationContext.close();
      System.out.println("Spring 应用上下文已关闭...");
  }

  @Bean(initMethod = "initUserFactory", destroyMethod = "doDestroy")
  @Lazy(value = true)
  public UserFactory userFactory() {
      return new DefaultUserFactory();
  }
}

03 延迟初始化Spring Bean

XML
Java注解 @Lazy(true)
spring容器返回的bean和延迟初始化的bean有什么区别？
- 非延迟：在spring上下文加载完成就已经初始化了
- 延迟：是在getBean的时候才初始化
- // Instantiate all remaining (non-lazy-init) singletons.
- finishBeanFactoryInitialization(beanFactory);
  04 销毁Spring Bean

@PreDestory

org.springframework.context.annotation.CommonAnnotationBeanPostProcessor#CommonAnnotationBeanPostProcessor
public CommonAnnotationBeanPostProcessor() {
  setOrder(Ordered.LOWEST_PRECEDENCE - 3);
  setInitAnnotationType(PostConstruct.class);
  setDestroyAnnotationType(PreDestroy.class);
  ignoreResourceType("javax.xml.ws.WebServiceContext");
}

实现DisposableBean接口的destory()方法

String[] disposableBeanNames;
synchronized (this.disposableBeans) {
  disposableBeanNames = StringUtils.toStringArray(this.disposableBeans.keySet());
}

自定义销毁方法
- xml<bean destory=”destory” .. />
- Java注解 @Bean(destory=”destory”)
- Java API AbstractBeanDefinition#setDestoryMethodName(string)
三者执行顺序 1-2-3
- // Destroy all cached singletons in the context’s BeanFactory.
- destroyBeans();
  05 垃圾回收Spring Bean
关闭spring容器
执行GC

spring bean覆盖 finalize()方法

public class BeanGarbageCollectionDemo {

  public static void main(String[] args) throws InterruptedException {
      // 创建 BeanFactory 容器
      AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
      // 注册 Configuration Class（配置类）
      applicationContext.register(BeanInitializationDemo.class);
      // 启动 Spring 应用上下文
      applicationContext.refresh();
      // 关闭 Spring 应用上下文
      applicationContext.close();
      Thread.sleep(5000L);
      // 强制触发 GC
      System.gc();
      Thread.sleep(5000L);
  }
}

06将外部单体对象注入到IOC中

public class SingletonBeanRegistrationDemo {

  public static void main(String[] args) throws InterruptedException {
      // 创建 BeanFactory 容器
      AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
      // 创建一个外部 UserFactory 对象
      UserFactory userFactory = new DefaultUserFactory();
      SingletonBeanRegistry singletonBeanRegistry = applicationContext.getBeanFactory();
      // 注册外部单例对象
      singletonBeanRegistry.registerSingleton("userFactory", userFactory);
      // 启动 Spring 应用上下文
      applicationContext.refresh();
      // 通过依赖查找的方式来获取 UserFactory
      UserFactory userFactoryByLookup = applicationContext.getBean("userFactory", UserFactory.class);
      System.out.println("userFactory  == userFactoryByLookup : " + (userFactory == userFactoryByLookup));
      // 关闭 Spring 应用上下文
      applicationContext.close();
  }
}

01 实例化Spring Bean

常规

特殊

02 初始化Spring Bean

03 延迟初始化Spring Bean

04 销毁Spring Bean

05 垃圾回收Spring Bean

06将外部单体对象注入到IOC中