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Spring的refresh()方法相关异常

时间:2015-04-11 20:52:30      阅读:241      评论:0      收藏:0      [点我收藏+]

标签:spring   refresh   initialized   

如果是经常使用Spring,特别有自己新建ApplicationContext对象的经历的人,肯定见过这么几条异常消息:
1.LifecycleProcessor not initialized - call ‘refresh‘ before invoking lifecycle methods via the context: ......
2.BeanFactory not initialized or already closed - call ‘refresh‘ before accessing beans via the ApplicationContext
3.ApplicationEventMulticaster not initialized - call ‘refresh‘ before multicasting events via the context: ......

第一条消息是说LifecycleProcessor对象没有初始化,在调用context的生命周期方法之前必须调用‘refresh‘方法
第二条消息是说BeanFactory对象没有初始化或已经关闭了,使用ApplicationContext获取Bean之前必须调用‘refresh‘方法
第三条消息是说ApplicationEventMulticaster对象没有初始化,在context广播事件之前必须调用‘refresh‘方法

这几条异常消息都与refresh方法有关,那抛出这些异常的原因到底是什么,为什么在这么多情况下一定要先调用refresh方法(定义在AbstractApplicationContext类中),
在此这前我们先看看refresh方法中又干了些什么?

public void refresh() throws BeansException, IllegalStateException {
	synchronized (this.startupShutdownMonitor) {
		//刷新之前的准备工作,包括设置启动时间,是否激活标识位,初始化属性源(property source)配置
		prepareRefresh();

		//由子类去刷新BeanFactory(如果还没创建则创建),并将BeanFactory返回
		ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

		//准备BeanFactory以供ApplicationContext使用
		prepareBeanFactory(beanFactory);

		try {
			//子类可通过格式此方法来对BeanFactory进行修改
			postProcessBeanFactory(beanFactory);

			//实例化并调用所有注册的BeanFactoryPostProcessor对象
			invokeBeanFactoryPostProcessors(beanFactory);

			//实例化并调用所有注册的BeanPostProcessor对象
			registerBeanPostProcessors(beanFactory);

			//初始化MessageSource
			initMessageSource();

			//初始化事件广播器
			initApplicationEventMulticaster();

			//子类覆盖此方法在刷新过程做额外工作
			onRefresh();

			//注册应用监听器ApplicationListener
			registerListeners();

			//实例化所有non-lazy-init bean
			finishBeanFactoryInitialization(beanFactory);

			//刷新完成工作,包括初始化LifecycleProcessor,发布刷新完成事件等
			finishRefresh();
		}

		catch (BeansException ex) {
			// Destroy already created singletons to avoid dangling resources.
			destroyBeans();

			// Reset 'active' flag.
			cancelRefresh(ex);

			// Propagate exception to caller.
			throw ex;
		}
	}
}

与此三条异常消息相关的方法分别为:finishRefresh();obtainFreshBeanFactory();initApplicationEventMulticaster();

protected void finishRefresh() {
	// //初始化LifecycleProcessor
	initLifecycleProcessor();

	// Propagate refresh to lifecycle processor first.
	getLifecycleProcessor().onRefresh();

	// Publish the final event.
	publishEvent(new ContextRefreshedEvent(this));

	// Participate in LiveBeansView MBean, if active.
	LiveBeansView.registerApplicationContext(this);
}

如果没有调用finishRefresh方法,则lifecycleProcessor成员为null。

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
	refreshBeanFactory();//刷新BeanFactory,如果beanFactory为null,则创建
	ConfigurableListableBeanFactory beanFactory = getBeanFactory();
	if (logger.isDebugEnabled()) {
		logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
	}
	return beanFactory;
}

refreshBeanFactory()为一抽象方法,真正实现在AbstractRefreshableApplicationContext类中:

@Override
protected final void refreshBeanFactory() throws BeansException {
	if (hasBeanFactory()) {//如果beanFactory已经不为null,则销毁beanFactory中的Bean后自行关闭
		destroyBeans();
		closeBeanFactory();
	}
	try {
		DefaultListableBeanFactory beanFactory = createBeanFactory();//创建beanFactory
		beanFactory.setSerializationId(getId());
		customizeBeanFactory(beanFactory);
		loadBeanDefinitions(beanFactory);
		synchronized (this.beanFactoryMonitor) {
			this.beanFactory = beanFactory;//对beanFactory成员进行赋值
		}
	}
	catch (IOException ex) {
		throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
	}
}

如果没有调用obtainFreshBeanFactory()方法则beanFactory成员为null。

protected void initApplicationEventMulticaster() {
	ConfigurableListableBeanFactory beanFactory = getBeanFactory();
	if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
		this.applicationEventMulticaster =
				beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
		if (logger.isDebugEnabled()) {
			logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
		}
	}
	else {
		this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
		beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
		if (logger.isDebugEnabled()) {
			logger.debug("Unable to locate ApplicationEventMulticaster with name '" +
					APPLICATION_EVENT_MULTICASTER_BEAN_NAME +
					"': using default [" + this.applicationEventMulticaster + "]");
		}
	}
}

而这三个方法调用都在refresh()方法中,由上面的分析可知,如果没有调用refresh方法,则上下文中的lifecycleProcessor,beanFactory,applicationEventMulticaster成员都会为null。至此可以来详细分析这三条异常消息的缘由了。
下面是针对上面三条异常消息的三段测试代码,顺序相对应:

1. public static void main(String[] args) {
	ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext();
	applicationContext.setConfigLocation("application-context.xml");
	applicationContext.start();
	applicationContext.close();
}
2. public static void main(String[] args) {
	ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext();
	applicationContext.setConfigLocation("application-context.xml");
	applicationContext.getBean("xtayfjpk");
	applicationContext.close();
}
3. public static void main(String[] args) {
	GenericApplicationContext parent = new GenericApplicationContext();
	AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
	context.setParent(parent);
	context.refresh();
	context.start();
	context.close();
}

对于第一条异常消息,异常堆栈出错在applicationContext.start();下面是start()方法源码:

public void start() {
	getLifecycleProcessor().start();
	publishEvent(new ContextStartedEvent(this));
}

可以看到start()方法中要先获取lifecycleProcessor对象,而默认构造方法中并没用调用refresh方法,所以lifecycleProcessor为null,故而在getLifecycleProcessor()方法中抛出了此异常消息。这其中提到了生命周期方法,其实就是定义在org.springframework.context.Lifecycle接口中的start(), stop(), isRunning()三个方法,如果是刚开始学习Spring的话,创建ClassPathXmlApplicationContext对象时应该是这样的:ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("application-context.xml");这样直接调用start()方法却又不会出现异常,这是为什么呢?这是因为ClassPathXmlApplicationContext(String configLocation)这个构造方法最终调用的是:

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent) throws BeansException {
	super(parent);
	setConfigLocations(configLocations);
	if (refresh) {//refresh传递值为true,这样就自动调用了refresh方法进行了刷新
		refresh();
	}
}

第二条异常消息,异常堆栈出错在applicationContext.getBean("xtayfjpk"),applicationContext.getBean()方法调用的是上下文中beanFactory的getBean()方法实现的,获取BeanFactory对象的代码在其基类ConfigurableListableBeanFactory中的getBeanFactory()方法中:

@Override
public final ConfigurableListableBeanFactory getBeanFactory() {
	synchronized (this.beanFactoryMonitor) {
		if (this.beanFactory == null) {
			throw new IllegalStateException("BeanFactory not initialized or already closed - " +
					"call 'refresh' before accessing beans via the ApplicationContext");
		}
		return this.beanFactory;
	}
}

由于ClassPathXmlApplicationContext的默认构造方法没有调用refresh()方法,所以beanFactory为null,因此抛出异常。


第三条异常消息,异常堆栈出错在context.refresh(),但是如果没有设置父上下文的话context.setParent(parent),例子代码是不会出现异常的。这是因为在refresh方法中的finishRefresh()方法调用了publishEvent方法:

public void publishEvent(ApplicationEvent event) {
	Assert.notNull(event, "Event must not be null");
	if (logger.isTraceEnabled()) {
		logger.trace("Publishing event in " + getDisplayName() + ": " + event);
	}
	getApplicationEventMulticaster().multicastEvent(event);
	if (this.parent != null) {
		this.parent.publishEvent(event);
	}
}

从上面可以看到:如果父上下文不为null,则还需要调用父容器的pushlishEvent方法,而且在该方法中调用了getApplicationEventMulticaster()方法以获取一个事件广播器,问题就出现在这里:

private ApplicationEventMulticaster getApplicationEventMulticaster() throws IllegalStateException {
	if (this.applicationEventMulticaster == null) {//如果为null则抛异常
		throw new IllegalStateException("ApplicationEventMulticaster not initialized - " +
				"call 'refresh' before multicasting events via the context: " + this);
	}
	return this.applicationEventMulticaster;
}

而applicationEventMulticaster就是在refresh方法中的initApplicationEventMulticaster方法在实例化的,则于父上下文没有调用过refresh方法所以父上下文的applicationEventMulticaster成员为null,因此抛出异常。


综上所述,其实这三条异常消息的根本原因只有一个,就是当一个上下文对象创建后没有调用refresh()方法。在Spring中ApplicationContext实现类有很多,有些实现类在创建的过程中自动调用了refresh()方法,而有些又没有,如果没有则需要自己手动调用refresh()方法。一般说来实现WebApplicationContext接口的实现类以及使用默认构造方法创建上下文对象时不会自动refresh()方法,其它情况则会自动调用。

Spring的refresh()方法相关异常

标签:spring   refresh   initialized   

原文地址:http://blog.csdn.net/xtayfjpk/article/details/44998599

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