Spring源码学习-4.IoC容器其他特征分析

1.ApplicationContext和Bean的初始化与销毁

对于Beanfactory特别是 ApplicationContext,容器自身也有一个初始化与销毁关闭的过程,下面我们一起来探究这个过程

在prepareBeanFactory这个方法里面为BeanFactory设置了classLoad等属性

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// Tell the internal bean factory to use the context's class loader.
beanFactory.setBeanClassLoader(getClassLoader());

// Populate the bean factory with context-specific resource editors.
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this));

// Configure the bean factory with context callbacks.
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

// BeanFactory interface not registered as resolvable type in a plain factory.
// MessageSource registered (and found for autowiring) as a bean.
beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
beanFactory.registerResolvableDependency(ApplicationContext.class, this);

// Detect a LoadTimeWeaver and prepare for weaving, if found.
if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME) && JdkVersion.isAtLeastJava15()) {
// Register the (JDK 1.5 specific) LoadTimeWeaverAwareProcessor.
try {
Class ltwapClass = ClassUtils.forName(
"org.springframework.context.weaving.LoadTimeWeaverAwareProcessor",
AbstractApplicationContext.class.getClassLoader());
BeanPostProcessor ltwap = (BeanPostProcessor) BeanUtils.instantiateClass(ltwapClass);
((BeanFactoryAware) ltwap).setBeanFactory(beanFactory);
beanFactory.addBeanPostProcessor(ltwap);
}
catch (ClassNotFoundException ex) {
throw new IllegalStateException("Spring's LoadTimeWeaverAwareProcessor class is not available");
}
// Set a temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
}

同样,容器在关闭时,也会有 一系列的操作,这些操作在DoClose方法中

protected void doClose() {
if (isActive()) {
if (logger.isInfoEnabled()) {
logger.info("Closing " + this);
}
try {
// Publish shutdown event.
publishEvent(new ContextClosedEvent(this));
}
catch (Throwable ex) {
logger.error("Exception thrown from ApplicationListener handling ContextClosedEvent", ex);
}
// Stop all Lifecycle beans, to avoid delays during individual destruction.
Map lifecycleBeans = getLifecycleBeans();
for (Iterator it = new LinkedHashSet(lifecycleBeans.keySet()).iterator(); it.hasNext();) {
String beanName = (String) it.next();
doStop(lifecycleBeans, beanName);
}
// Destroy all cached singletons in the context's BeanFactory.
destroyBeans();
// Close the state of this context itself.
closeBeanFactory();
onClose();
synchronized (this.activeMonitor) {
this.active = false;
}
}
}

2.lazy-init属性与预实例化

IoC容器初始化过程中,只完成了对Bean的定位,载入和注册,但是并没有对Bean进行依赖注入,依赖注入发生在调用getBean时,但是也有一个例外,就是lazy-init属性,他会在
初始化时就对Bean进行依赖注入.

lazy-init属性的实现是在refresh这个方法中,我们来重新看下这个方法

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();
<span style="white-space:pre">				</span>//在这里对lazy-init属性进行处理
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);

// Last step: publish corresponding event.
finishRefresh();
}

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

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

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

完成对Bean的注册后,调用这个方法,对lazy-init属性进行处理

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// Stop using the temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(null);

// Allow for caching all bean definition metadata, not expecting further changes.
beanFactory.freezeConfiguration();
<span style="white-space:pre">		</span>//在这里开始处理
// Instantiate all remaining (non-lazy-init) singletons.
beanFactory.preInstantiateSingletons();
}

public void preInstantiateSingletons() throws BeansException {
if (this.logger.isInfoEnabled()) {
this.logger.info("Pre-instantiating singletons in " + this);
}
//检测BeanDefinition需要提前依赖注入的对象
synchronized (this.beanDefinitionMap) {
for (Iterator it = this.beanDefinitionNames.iterator(); it.hasNext();) {
String beanName = (String) it.next();
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
if (isFactoryBean(beanName)) {
FactoryBean factory = (FactoryBean) getBean(FACTORY_BEAN_PREFIX + beanName);
if (factory instanceof SmartFactoryBean && ((SmartFactoryBean) factory).isEagerInit()) {
//实现依赖注入
getBean(beanName);
}
}
else {
//实现依赖注入
getBean(beanName);
}
}
}
}
}

3.FactoryBean的实现

FactorBean的作用是为应用生成需要的对象,如ProxyFactoryBean等,
在doGetBean中调用了
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);

然后又调用了
object = getObjectFromFactoryBean(factory, beanName, !synthetic);

protected Object getObjectForBeanInstance(
Object beanInstance, String name, String beanName, RootBeanDefinition mbd) {

//如果不是对FactoryBean的调用,那么结束
// Don't let calling code try to dereference the factory if the bean isn't a factory.
if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {
throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());
}

// Now we have the bean instance, which may be a normal bean or a FactoryBean.
// If it's a FactoryBean, we use it to create a bean instance, unless the
// caller actually wants a reference to the factory.
if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
return beanInstance;
}

Object object = null;
if (mbd == null) {
object = getCachedObjectForFactoryBean(beanName);
}
if (object == null) {
// Return bean instance from factory.
FactoryBean factory = (FactoryBean) beanInstance;
// Caches object obtained from FactoryBean if it is a singleton.
if (mbd == null && containsBeanDefinition(beanName)) {
mbd = getMergedLocalBeanDefinition(beanName);
}
boolean synthetic = (mbd != null && mbd.isSynthetic());
//从FactoryBean中得到Bean
object = getObjectFromFactoryBean(factory, beanName, !synthetic);
}
return object;
}

protected Object getObjectFromFactoryBean(FactoryBean factory, String beanName, boolean shouldPostProcess) {
if (factory.isSingleton() && containsSingleton(beanName)) {
synchronized (getSingletonMutex()) {
Object object = this.factoryBeanObjectCache.get(beanName);
if (object == null) {
object = doGetObjectFromFactoryBean(factory, beanName, shouldPostProcess);
this.factoryBeanObjectCache.put(beanName, (object != null ? object : NULL_OBJECT));
}
return (object != NULL_OBJECT ? object : null);
}
}
else {
return doGetObjectFromFactoryBean(factory, beanName, shouldPostProcess);
}
}

private Object doGetObjectFromFactoryBean(
final FactoryBean factory, final String beanName, final boolean shouldPostProcess)
throws BeanCreationException {

AccessControlContext acc = AccessController.getContext();
return AccessController.doPrivileged(new PrivilegedAction() {
public Object run() {
Object object;

try {
//从Factory的getBean从FactoryBean中获取Bean
object = factory.getObject();
}
catch (FactoryBeanNotInitializedException ex) {
throw new BeanCurrentlyInCreationException(beanName, ex.toString());
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "FactoryBean threw exception on object creation", ex);
}

// Do not accept a null value for a FactoryBean that's not fully
// initialized yet: Many FactoryBeans just return null then.
if (object == null && isSingletonCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(
beanName, "FactoryBean which is currently in creation returned null from getObject");
}

if (object != null && shouldPostProcess) {
try {
object = postProcessObjectFromFactoryBean(object, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "Post-processing of the FactoryBean's object failed", ex);
}
}

return object;
}
}, acc);
}

这里使用的就是工程模式,getObjectForBeanInstance就想相当于createInstance

4.BeanPostProcessor的实现

BeanPostProcessor是Bean的后置处理器

依赖注入中对于后置处理器的实现发生在population后面,是依赖注入的一个重要组成部分.

5.autowiring(自动依赖装配)

如果当前Bean配置了Autowiring属性,那么在populate中,就会根据name或者type,查找同名的bean,并触发另一个bean的依赖注入与生成

//通过nama自动完成依赖注入
protected void autowireByName(
String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {

String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
for (int i = 0; i < propertyNames.length; i++) {
String propertyName = propertyNames[i];
if (containsBean(propertyName)) {
Object bean = getBean(propertyName);
pvs.addPropertyValue(propertyName, bean);
registerDependentBean(propertyName, beanName);
if (logger.isDebugEnabled()) {
logger.debug("Added autowiring by name from bean name '" + beanName +
"' via property '" + propertyName + "' to bean named '" + propertyName + "'");
}
}
else {
if (logger.isTraceEnabled()) {
logger.trace("Not autowiring property '" + propertyName + "' of bean '" + beanName +
"' by name: no matching bean found");
}
}
}
}