这两天对Dubbo代码里面一个使用 FactoryBean
的地方有很多疑惑, 才发现自己对我们最熟悉的Spring框架好多地方,都没搞清楚为什么要这样用。
废话少说, Spring作为一个IOC工厂, 自然是为了生产Bean而生,那么就去看下Spring是如何管理,并生产Bean的。
我直接用 AnnotationConfigApplicationContext
来测试,
public static void main(String[] args) throws Exception {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(TestConfiguration.class);
Dog dog = (Dog) context.getBean("dog");
dog.test();
context.start();
System.in.read();
}
@Configuration
@ComponentScan(value = "org.apache.dubbo.demo.provider")
public class TestConfiguration {
}
在new 一个 AnnotationConfigApplicationContext 的时候,先注册我们的Configuration, 然后refresh() 刷新容器启动。
/**
* Create a new AnnotationConfigApplicationContext, deriving bean definitions
* from the given annotated classes and automatically refreshing the context.
* @param annotatedClasses one or more annotated classes,
* e.g. {@link Configuration @Configuration} classes
*/
public AnnotationConfigApplicationContext(Class<?>... annotatedClasses) {
this();
register(annotatedClasses);
refresh();
}
refresh方法是继承于AbstractApplicationContext抽象类,是在接口ConfigurableApplicationContext中定义的。其在抽象类中源码如下:
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
refresh方法大致描述了Spring IOC
容器的初始化过程,第一步prepareRefresh
主要是做一些准备工作,如准备应用环境、设置启动时间、设置属性源初始化标志
等。
/**
* Prepare this context for refreshing, setting its startup date and
* active flag as well as performing any initialization of property sources.
*/
protected void prepareRefresh() {
this.startupDate = System.currentTimeMillis();
this.closed.set(false);
this.active.set(true);
if (logger.isInfoEnabled()) {
logger.info("Refreshing " + this);
}
// Initialize any placeholder property sources in the context environment
initPropertySources();
// Validate that all properties marked as required are resolvable
// see ConfigurablePropertyResolver#setRequiredProperties
getEnvironment().validateRequiredProperties();
// Allow for the collection of early ApplicationEvents,
// to be published once the multicaster is available...
this.earlyApplicationEvents = new LinkedHashSet<ApplicationEvent>();
}
第二步ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory()
,这一步是获取更新后的子类Bean工厂。代码如下:
/**
* Tell the subclass to refresh the internal bean factory.
* @return the fresh BeanFactory instance
* @see #refreshBeanFactory()
* @see #getBeanFactory()
*/
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
refreshBeanFactory();
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}
两个方法refreshBeanFactory()
和getBeanFactory()
,这两个方法均为抽象方法,在子类 refreshBeanFactory
实现,如下所示:
/**
* This implementation performs an actual refresh of this context's underlying
* bean factory, shutting down the previous bean factory (if any) and
* initializing a fresh bean factory for the next phase of the context's lifecycle.
*/
@Override
protected final void refreshBeanFactory() throws BeansException {
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory();
}
try {
DefaultListableBeanFactory beanFactory = createBeanFactory();
beanFactory.setSerializationId(getId());
customizeBeanFactory(beanFactory);
loadBeanDefinitions(beanFactory);
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
先判断是否存在BeanFactory,若存在则直接销毁原BeanFactory,先销毁工厂中的Beans,再关闭工bean厂。之后创建新的Bean工厂,其方法为createBeanFactory,如下所示:
protected DefaultListableBeanFactory createBeanFactory() {
return new DefaultListableBeanFactory(getInternalParentBeanFactory());
}
创建的Bean工厂是默认的bean工厂DefaultListableBeanFactory
类型。创建完新的bean工厂后便会根据上下文进行初始化(customizeBeanFactory) 定制化,加载bean定义(loadBeanDefinitions)。其中,loadBeanDefinitions
为抽象方法,