转载

Spring SmartInitializingSingleton 原荐

OrangeJoke的个人空间 spring

正文

Spring SmartInitializingSingleton

原

荐

OrangeJoke 发布于 39分钟前

字数 619

阅读 2

面试：你懂什么是分布式系统吗？Redis分布式锁都不会？>>> Spring SmartInitializingSingleton 原荐

使用场景

我们在这样的场景下使用，当ApplicationContext 加载完所有的Bean之后，我们来做一些我们想要的操作。下面是使用方法：

public class MyRegister implements SmartInitializingSingleton {
    Logger logger = LoggerFactory.getLogger(MyRegister.class);
    private final DefaultListableBeanFactory beanFactory;
    public MyRegister(DefaultListableBeanFactory beanFactory) {
        this.beanFactory = beanFactory;
    }
    @Override
    public void afterSingletonsInstantiated() {
        Map<String, Tiger> redisCacheProviderMap = beanFactory.getBeansOfType(Tiger.class);
        logger.info("tiger pre init");
    }
}

接口说明

/**
 *<p> Callback interface triggered at the end of the singleton pre-instantiation phase
 * during {@link BeanFactory} bootstrap.
 *
 * <p>This callback variant is somewhat similar to
 * {@link org.springframework.context.event.ContextRefreshedEvent} but doesn't
 * require an implementation of {@link org.springframework.context.ApplicationListener},
 * with no need to filter context references across a context hierarchy etc.
 * It also implies a more minimal dependency on just the {@code beans} package
 * and is being honored by standalone {@link ListableBeanFactory} implementations,
 * not just in an {@link org.springframework.context.ApplicationContext} environment.
 */
 public interface SmartInitializingSingleton {}

主要摘取上面一段说明来解答疑惑：

这个接口的功能类似ContextRefreshedEvent（由Configua>bleApplicationContext.refresh()触发），ContextRefreshedEvent的具体阶段来看下面具体文档。

Published when the ApplicationContext is initialized or refreshed (for example, by using the refresh() method on the ConfigurableApplicationContext interface). Here, “initialized” means that all beans are loaded, post-processor beans are detected and activated, singletons are pre-instantiated, and the ApplicationContext object is ready for use. As long as the context has not been closed, a refresh can be triggered multiple times, provided that the chosen ApplicationContext actually supports such “hot” refreshes. For example, XmlWebApplicationContext supports hot refreshes, but GenericApplicationContext does not.

对比接收事件的优点：就是不需要实现ApplicationListener，引用也更加简单（不需要获取ApplicationContext），对应性能也会更好一点。

文档里说到 pre-instantiation phase 这个比较疑惑，实际上这里的pre-instantiation对应SmartInitializingSingleton的执行过程·

public abstract class AbstractApplicationContext extends DefaultResourceLoader
implements ConfigurableApplicationContext, DisposableBean {

	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
		// 省略其他步骤.........
		// Instantiate all remaining (non-lazy-init) singletons.
		finishBeanFactoryInitialization(beanFactory);
		// Last step: publish corresponding event.
		finishRefresh();
		}
}

finishBeanFactoryInitialization（ConfigurableListableBeanFactory beanFactory）
{
  //省略其他步骤.......
  // Instantiate all remaining (non-lazy-init) singletons.
  beanFactory.preInstantiateSingletons();
}

所以结论就是SmartInitializingSingleton的方法就是在finishRefresh() 触发ContextRefreshedEvent事件前执行的。所以上面的pre-instantiation phase说的就是beanFactory.preInstantiateSingletons()这方法执行。

实现

beanFactory.preInstantiateSingletons();

// Trigger post-initialization callback for all applicable beans...
for (String beanName : beanNames) {
			Object singletonInstance = getSingleton(beanName);
			if (singletonInstance instanceof SmartInitializingSingleton) {
				final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
				if (System.getSecurityManager() != null) {
					AccessController.doPrivileged(new PrivilegedAction<Object>() {
						@Override
						public Object run() {
							smartSingleton.afterSingletonsInstantiated();
							return null;
						}
					}, getAccessControlContext());
				}
				else {
					smartSingleton.afterSingletonsInstantiated();
				}
			}
}

DefaultListableBeanFactory 这个类的实例是怎么构造注入的？构造函数注入。

另外的方法：Bean获取ApplicationContext是需要实现Aware接口的，类似这样：

//spring @EventListner 处理器
public class EventListenerMethodProcessor implements SmartInitializingSingleton, ApplicationContextAware {
	private ConfigurableApplicationContext applicationContext;

	@Override
	public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
		Assert.isTrue(applicationContext instanceof ConfigurableApplicationContext,
				"ApplicationContext does not implement ConfigurableApplicationContext");
		this.applicationContext = (ConfigurableApplicationContext) applicationContext;
	}

上一篇： Java Async IO Library: Quasar (use Fiber)

下一篇： spring boot deploy with javaagent

OrangeJoke

粉丝 37

博文 54

码字总数 35975

作品 0

江北

高级程序员

提问

相关文章最新文章

EventListener原理

目录目录流程 initApplicationEventMulticaster() registerListeners() finishRefresh() publishEvent() @EventListener处理流程容器的刷新流程如下：其中与EventListener有关联的步骤 ......

4rnold

2018/08/12

聊聊spring cloud的AsyncLoadBalancerAutoConfiguration

序本文主要研究一下AsyncLoadBalancerAutoConfiguration AsyncLoadBalancerAutoConfiguration spring-cloud-commons-2.0.0.RELEASE-sources.jar!/org/springframework/cloud/client/loadba......

go4it

2018/07/17

聊聊spring cloud的LoadBalancerAutoConfiguration

序本文主要研究一下spring cloud的LoadBalancerAutoConfiguration RibbonAutoConfiguration spring-cloud-netflix-ribbon-2.0.0.RC2-sources.jar!/org/springframework/cloud/netflix/ribb......

go4it

2018/07/16

深入Spring Boot：Spring Context的继承关系和影响

前言对于一个简单的Spring boot应用，它的spring context是只会有一个。非web spring boot应用，context是 web spring boot应用，context是是spring boot里自己实现的一个context，主要功...

横云断岭

2018/12/10

Spring Bean生命周期-finishBeanFactoryInitialization(九)

这个方法应该是ApplicationContext刷新的时候，最重要的方法了，因为所有的bean，如果不是lazy-init的都会在这一步进行实例化，并且做一些处理。狭义上的Bean生命周期就在这一步进行完成，我...

Real_man

2018/10/12

没有更多内容

加载失败，请刷新页面