经过上面几节的简单介绍我们了解了spring的一些组件,现在我们来分析一下AbstractApplicationContext中的refresh()这个核心方法吧~
用我们上一节的代码,debug进入refresh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();
// 准备beanfactory来使用这个上下文.做一些准备工作,例如classloader,beanfactoryPostProcessor等
prepareBeanFactory(beanFactory);
try {
//允许上下文的子类去执行postProcessor
postProcessBeanFactory(beanFactory);
// 开始执行注册到该上下文的BeanFactoryPostProcessors
invokeBeanFactoryPostProcessors(beanFactory);
// 开始注册BeanPostProcessor来拦截其他的bean的初始化过程
registerBeanPostProcessors(beanFactory);
// 初始化消息源
initMessageSource();
//注册上下文事件的广播集
initApplicationEventMulticaster();
//初始化一些特殊的bean
onRefresh();
//查询并校验监听器并注册
registerListeners();
// 实例化所有非懒加载的所有bean
finishBeanFactoryInitialization(beanFactory);
//最后一步发布所有的运用
finishRefresh();
}
catch (BeansException ex) {
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
}
}
结合上一节我们给出的spring的一些组件实例化的初始化顺序图:
我们先看invokeBeanFactoryPostProcessors(beanFactory)这个方法
<span style="color:#000000;">protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
// 先执行BeanDefinitionRegistryPostProcessors,因为我们这边没有实现这个接口,先暂时忽略,这段代码
Set<String> processedBeans = new HashSet<String>();
if (beanFactory instanceof BeanDefinitionRegistry) {
BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
List<BeanDefinitionRegistryPostProcessor> registryPostProcessors =
new LinkedList<BeanDefinitionRegistryPostProcessor>();
for (BeanFactoryPostProcessor postProcessor : getBeanFactoryPostProcessors()) {
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
BeanDefinitionRegistryPostProcessor registryPostProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
registryPostProcessor.postProcessBeanDefinitionRegistry(registry);
registryPostProcessors.add(registryPostProcessor);
}
else {
regularPostProcessors.add(postProcessor);
}
}
Map<String, BeanDefinitionRegistryPostProcessor> beanMap =
beanFactory.getBeansOfType(BeanDefinitionRegistryPostProcessor.class, true, false);
List<BeanDefinitionRegistryPostProcessor> registryPostProcessorBeans =
new ArrayList<BeanDefinitionRegistryPostProcessor>(beanMap.values());
OrderComparator.sort(registryPostProcessorBeans);
for (BeanDefinitionRegistryPostProcessor postProcessor : registryPostProcessorBeans) {
postProcessor.postProcessBeanDefinitionRegistry(registry);
}
invokeBeanFactoryPostProcessors(registryPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(registryPostProcessorBeans, beanFactory);
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
processedBeans.addAll(beanMap.keySet());
}
else {
// Invoke factory processors registered with the context instance.
invokeBeanFactoryPostProcessors(getBeanFactoryPostProcessors(), beanFactory);
}
//在beanFactory中获取实现BeanFactoryPostProcessor这个接口的bean的名称
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
// 将获取到的BeanFactoryPostProcessors的bean分类,根据这些bean是否也实现了PriorityOrdered,Ordered这些接口,或者其他,因为我们的例子中
// 并没有实现这些接口,所以我们的"springMultiBean"这个在spring-init.xml中(代码见上一节)定义的bean将进入nonOrderedPostProcessorNames.add(ppName)这个代码块
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
List<String> orderedPostProcessorNames = new ArrayList<String>();
List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
for (String ppName : postProcessorNames) {
if (processedBeans.contains(ppName)) {
// skip - already processed in first phase above
}
else if (isTypeMatch(ppName, PriorityOrdered.class)) {
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
}
else if (isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
//首先先执行实现“权重排序”的BeanFactoryPostProcessors,我们的bean“springMultiBean”并没有实现,所以不管
OrderComparator.sort(priorityOrderedPostProcessors);
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
// 然后执行实现“排序”的接口的BeanFactoryPostProcessors,我们也没有实现,暂时不看这块代码块
List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
for (String postProcessorName : orderedPostProcessorNames) {
orderedPostProcessors.add(getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
OrderComparator.sort(orderedPostProcessors);
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
// 最后执行“其他”的BeanFactoryPostProcessors,这边就即将执行我们的springMultiBean这个bean的BeanFactoryPostProcessors
// 这边新建了一个List类型是BeanFactoryPostProcessor,好了,这边就开始需要实例化实现BeanFactoryPostProcessor的bean了,否则,
// 无法放入List<BeanFactoryPostProcessor> 也就是说,如果想先执行BeanFactoryPostProcessor的方法,必须先实例化实现该接口的bean
List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
//可能我们的配置文件有很多的bean实现了BeanFactoryPostProcessors,循环bean的名字
for (String postProcessorName : nonOrderedPostProcessorNames) {
//底下的方法块是核心块,getBean这个方法就是初始化实现BeanFactoryPostProcessor这个接口的bean了,实例化好了之后放入List<BeanFactoryPostProcessor>
nonOrderedPostProcessors.add(getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
//批量执行nonOrderedPostProcessors中的BeanFactoryPostProcessor
invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
}</span>
好了,到目前为止,我们应该知道了上一节的spring Bean实例化顺序的运行截图了:
也就是我们的上次总结的结论:
①首先执行的是构造函数
②然后执行的BeanNameAware这个接口中的方法
③然后执行的是BeanFactoryAware这个接口中的方法
④执行InitializingBean接口中的afterPropertiesSet的方法
⑤执行我们在xml中定义的init-method这个方法
⑥最后执行的是BeanFactoryPostProcessor这个方法
分析了invokeBeanFactoryPostProcessors这个方法,我们知道这个方法就是去执行BeanFactoryPostProcessor这个接口中的方法去的,上面代码注释也清楚的写到如果想先执行BeanFactoryPostProcessor这个接口的方法,必须先去实例化实现这个接口的Bean,也就是getBean这个方法了,即在执行⑥之前,①~⑤这些方法全是在getBean这个方法中执行的:
我们接着分析一下getBean这个超级核心的方法:
<span style="color:#000000;">@SuppressWarnings("unchecked")
protected <T> T doGetBean(
final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
throws BeansException {
final String beanName = transformedBeanName(name);
Object bean;
// Eagerly check singleton cache for manually registered singletons.
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {
if (logger.isDebugEnabled()) {
if (isSingletonCurrentlyInCreation(beanName)) {
logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
"' that is not fully initialized yet - a consequence of a circular reference");
}
else {
logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
}
}
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
// Fail if we're already creating this bean instance:
// We're assumably within a circular reference.
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// Check if bean definition exists in this factory.
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
String nameToLookup = originalBeanName(name);
if (args != null) {
// Delegation to parent with explicit args.
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
}
if (!typeCheckOnly) {
markBeanAsCreated(beanName);
}
try {
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// Guarantee initialization of beans that the current bean depends on.
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
for (String dependsOnBean : dependsOn) {
getBean(dependsOnBean);
registerDependentBean(dependsOnBean, beanName);
}
}
// Create bean instance.
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
public Object getObject() throws BeansException {
try {
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
// Explicitly remove instance from singleton cache: It might have been put there
// eagerly by the creation process, to allow for circular reference resolution.
// Also remove any beans that received a temporary reference to the bean.
destroySingleton(beanName);
throw ex;
}
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
else if (mbd.isPrototype()) {
// It's a prototype -> create a new instance.
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
else {
String scopeName = mbd.getScope();
final Scope scope = this.scopes.get(scopeName);
if (scope == null) {
throw new IllegalStateException("No Scope registered for scope '" + scopeName + "'");
}
try {
Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
public Object getObject() throws BeansException {
beforePrototypeCreation(beanName);
try {
return createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
}
});
bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
catch (IllegalStateException ex) {
throw new BeanCreationException(beanName,
"Scope '" + scopeName + "' is not active for the current thread; " +
"consider defining a scoped proxy for this bean if you intend to refer to it from a singleton",
ex);
}
}
}
catch (BeansException ex) {
cleanupAfterBeanCreationFailure(beanName);
throw ex;
}
}
// Check if required type matches the type of the actual bean instance.
if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
try {
return getTypeConverter().convertIfNecessary(bean, requiredType);
}
catch (TypeMismatchException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Failed to convert bean '" + name + "' to required type [" +
ClassUtils.getQualifiedName(requiredType) + "]", ex);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
return (T) bean;
}
</span>
好吧~,这个getBean的具体实现貌似有点长,一步步分析吧
第一部分:
这个方法首先先去singleton缓存中去找实例(这里我们肯定没找到,应该我们没有把我们的bean手动放入singletonObjects这个Map里面去)
第二部分:
这段代码是先获取该beanFactory父factory,希望从这些factory中获取,如果该beanfactory有父类,则希望用父类去实例化该bean,我们这边的beanfactory为null,暂不讨论~
接着看第三部分:
上图中
第一部分先标记目前的bean的正在创建
第二部分获取根据beanName该bean在beanfactory中的beanDefinitionMap的BeanDefinition,然后去获取这个bean依赖的bean,如果依赖的bean还没有创建,则先创建依赖的bean,递归调用,(Dependence Inject依赖注入的概念吧),如果找不到依赖,则忽略
第三部分:如果是单例(我们暂时只讨论如何创建单例)
则调用createBean()这个方法
好了,我们暂不看Prototype创建的过程,我们接着跟踪createBean()
上图中
第①部分:确保该bean的class是真实存在的,也就是该bean是可以classload可以找到加载的
第②部分:准备方法的重写
第③部分(很重要):请注意,这边有个return,也就是说这边可以返回bean了,但看注释:Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.这边就很清晰了,我们以前在beanPostProcessor的章节讲过,beanPostProcessor是可以临时修改bean的,它的优先级高于正常实例化bean的(也就是第四部分实例化的方法),如果beanPostProcessor能返回,则直接返回了,这边代码下次分析,我们还是先分析主要流程:
看第四部分:
doCreateBean(beanName, mbd, args)这个方法
这个方法首先初始化一个BeanWrapper,然后再看createBeanInstance()
这块代码主要是再次对bean做安全检查并确定该bean有默认的构造函数,createBeanInstance()这个方法最后一行
此时构造函数打印了我们system的内容,也就是第一个打印的
回到doCreateBean()这个方法
初始化bean,的确,现在bean已经实例化了,开始初始化该bean,进入initializeBean(…)这个方法
执行aware方法(看来beanFactoryAware和beanNameAware要执行了)
看源代码果然:
接着
开始执行初始化方法
首先先判断该bean是否实现了InitializingBean,如果实现了先执行afterPropertiesSet这个方法,然后如果该bean又执行了init-method,事实的确如此:
好了,到此为止,我们的第一个名为“springMultiBean”已经初始化了,实例化好的大体步骤我们已经基本了解了,大家先体会一下,我们spring-init.xml中还有一个bean”springOtherBean“没讲解,下次分解~正好一起重新分析细节~