在生成ApplicationContext過程中，AbstractRefreshableApplicationContext.refreshBeanFactory()完成舊BeanFactory關閉，創(chuàng)建新的BeanFactory，即new DefaultListableBeanFactory(…)。然后bean實例化時調(diào)用本類的preInstantiateSingletons方法。
類作用
BeanFactory作用是初始化和管理普通bean，因此DefaultListableBeanFactory是實現(xiàn)框架核心功能（IoC)的核心類。
類關系圖
DefaultListableBeanFactory類關系圖比較復雜，我們從頂向下梳理：
接口定義說明
AliasRegistry：頂層接口，別名注冊表接口，定義了管理bean的別名和名稱映射關系的基本方法，如注冊registerAlias(String name, String alias)、獲取（getAliases(String name)）和銷毀（removeAlias(String alias)）。
SingletonBeanRegistry：頂層接口，單實例bean注冊表接口，定義了管理單實例Bean的基本方法，如注冊（registerSingleton(String beanName, Object singletonObject)）和獲?。╣etSingleton(String beanName)。
BeanFactory：頂層接口，定義了訪問bean容器中bean的基本方法，只包括get或判斷（如is、contain）類方法。完全不包括BeanFactory是如何初始化并管理bean的方法。從使用者來說，只是按需使用即可，不關注如何實現(xiàn)。
HierarchicalBeanFactory：繼承BeanFactory，僅提供訪問繼承關系BeanFactory的方法，包括etParentBeanFactory()和containsLocalBean(String name)（當前BeanFactory（不是父BeanFactory）是否包含名為name的bean)。
ListableBeanFactory：是BeanFactory接口擴展，定義通過枚舉其所有bean實例的方法來訪問bean，而不是通過getBean(String beanName)這種單個按名稱查找bean。
AutowireCapableBeanFactory：是BeanFactory接口擴展，定義具備自動裝配能力的BeanFactory的實現(xiàn)方法。
ConfigurableBeanFactory：定義普通配置模式下BeanFactory的實現(xiàn)方法，如解析bean配置和bean的初始化。
ConfigurableListableBeanFactory：繼承了接口ListableBeanFactory, AutowireCapableBeanFactory, ConfigurableBeanFactory，并增加定義了分析和修改bean定義以及預實例化單實例bean的方法。
BeanDefinitionRegistry：BeanDefinition注冊表接口，定義對BeanDefinition（即bean的元數(shù)據(jù)）進行管理的方法。
SimpleAliasRegistry
實現(xiàn)接口AliasRegistry（bean alias存取及相關操作）。
DefaultSingletonBeanRegistry
主要實現(xiàn)單實例bean的緩存池，包括bean依賴關系管理（關系注冊和銷毀）。本類方法大量采用了synchronized存取緩存池（集合）。
繼承于SimpleAliasRegistry，并實現(xiàn)接口SingletonBeanRegistry（單實例bean的存取及相關操作）
FactoryBeanRegistrySupport
單實例bean管理中用到的關于factoryBean的相關方法實現(xiàn)。
AbstractBeanFactory
AbstractBeanFactory主要實現(xiàn)ConfigurableBeanFactory接口功能。BeanFactory大多數(shù)功能在該類實現(xiàn)，但核心方法createBean需在子類實現(xiàn)。
AbstractAutowireCapableBeanFactory
繼承AbstractBeanFactory，并實現(xiàn)接口AutowireCapableBeanFactory，即自動裝配相關功能在該類實現(xiàn)。
核心方法createBean在該類實現(xiàn)。
DefaultListableBeanFactory
繼承AbstractAutowireCapableBeanFactory，主要實現(xiàn)接口ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable。其中ConfigurableListableBeanFactory接口中的AutowireCapableBeanFactory, ConfigurableBeanFactory均在祖先類實現(xiàn)了，因此只需實現(xiàn)ListableBeanFactory接口方法。BeanDefinitionRegistry接口全部在這里實現(xiàn)。
類實現(xiàn)
DefaultListableBeanFactory繼承于AbstractAutowireCapableBeanFactory，大多數(shù)bean的創(chuàng)建、初始化等實現(xiàn)已在祖先類實現(xiàn)。本類主要實現(xiàn)BeanDefinitionRegistry接口和ListableBeanFactory接口。
DefaultListableBeanFactory(@Nullable BeanFactory parentBeanFactory)
DefaultListableBeanFactory構建類，實際構建在父類AbstractAutowireCapableBeanFactory完成，核心動作是動態(tài)生成子類的對象instantiationStrategy（CglibSubclassingInstantiationStrategy 用cgilib動態(tài)創(chuàng)建子類）。
DefaultListableBeanFactory構建代碼：
public DefaultListableBeanFactory(@Nullable BeanFactory parentBeanFactory) {
super(parentBeanFactory);
}
父類AbstractAutowireCapableBeanFactory構建代碼：
public AbstractAutowireCapableBeanFactory(@Nullable BeanFactory parentBeanFactory) {
this();
setParentBeanFactory(parentBeanFactory);
}
public AbstractAutowireCapableBeanFactory() {
super();
ignoreDependencyInterface(BeanNameAware.class);
ignoreDependencyInterface(BeanFactoryAware.class);
ignoreDependencyInterface(BeanClassLoaderAware.class);
//bean實例化器
this.instantiationStrategy = new CglibSubclassingInstantiationStrategy();
}
注1：CglibSubclassingInstantiationStrategy是Bean真正初始化類，詳見https://blog.csdn.net/davidwkx/article/details/131053503
preInstantiateSingletons
該方法是啟動過程中spring對單實例bean初始化的入口。
@Override
public void preInstantiateSingletons() throws BeansException {
if (logger.isTraceEnabled()) {
logger.trace("Pre-instantiating singletons in " + this);
}
// Iterate over a copy to allow for init methods which in turn register new bean definitions.
// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
// Trigger initialization of all non-lazy singleton beans...
for (String beanName : beanNames) {
//所有bean定義都統(tǒng)一成RootBeanDefinition 注1
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
//非抽象類、非延遲加載且是Singleton的bean進行初始化
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
//FactoryBean初始化
if (isFactoryBean(beanName)) {
//getBean通過有無前綴FACTORY_BEAN_PREFIX 識別是否FactoryBean 注2
Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
//FactoryBean中bean默認是延遲創(chuàng)建的，如果FactoryBean實現(xiàn)了SmartFactoryBean，重載isEagerInit()返回true，則表示立即對FactoryBean中的bean進行創(chuàng)建 注3
if (bean instanceof SmartFactoryBean<?> smartFactoryBean && smartFactoryBean.isEagerInit()) {
//FactoryBean創(chuàng)建bean
getBean(beanName);
}
}
//普通bean初始化
else {
getBean(beanName);
}
}
}
//如果bean實現(xiàn)了SmartInitializingSingleton接口，則在初始化后回調(diào)afterSingletonsInstantiated
// Trigger post-initialization callback for all applicable beans...
for (String beanName : beanNames) {
Object singletonInstance = getSingleton(beanName);
if (singletonInstance instanceof SmartInitializingSingleton smartSingleton) {
StartupStep smartInitialize = this.getApplicationStartup().start("spring.beans.smart-initialize")
.tag("beanName", beanName);
smartSingleton.afterSingletonsInstantiated();
smartInitialize.end();
}
}
}
注1：bean定義相關見：
注2：getBean(beanName)在AbstractBeanFactory實現(xiàn)，實際是調(diào)用AbstractBeanFactory.doGetBean(beanName, null, null, false)，詳見：https://blog.csdn.net/davidwkx/article/details/130963899
注3：如果beanName是FactoryBean的名稱，getBean(“&”+beanName) 是獲取 FactoryBean 本身，而getBean(beanName) 獲取的是 FactoryBean 創(chuàng)建出來的 bean 實例。文章來源：http://www.zghlxwxcb.cn/news/detail-479367.html
resolveDependency / doResolveDependency
解析指定beanName對應的屬性，并將解析到的屬性名放入autowiredBeanNames，根據(jù)類型查找依賴關系文章來源地址http://www.zghlxwxcb.cn/news/detail-479367.html
@Override
@Nullable
public Object resolveDependency(DependencyDescriptor descriptor, @Nullable String requestingBeanName,
@Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) throws BeansException {
descriptor.initParameterNameDiscovery(getParameterNameDiscoverer());
if (Optional.class == descriptor.getDependencyType()) {
// Optional類型的注入處理
return createOptionalDependency(descriptor, requestingBeanName);
}
else if (ObjectFactory.class == descriptor.getDependencyType() ||
ObjectProvider.class == descriptor.getDependencyType()) {
// ObjectFactory類型的注入處理
return new DependencyObjectProvider(descriptor, requestingBeanName);
}
else if (javaxInjectProviderClass == descriptor.getDependencyType()) {
// Jsr330注解的注入處理
return new Jsr330Factory().createDependencyProvider(descriptor, requestingBeanName);
}
else {
Object result = getAutowireCandidateResolver().getLazyResolutionProxyIfNecessary(
descriptor, requestingBeanName);
if (result == null) {
//非延遲加載的常規(guī)注入處理
result = doResolveDependency(descriptor, requestingBeanName, autowiredBeanNames, typeConverter);
}
return result;
}
}
@Nullable
public Object doResolveDependency(DependencyDescriptor descriptor, @Nullable String beanName,
@Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) throws BeansException {
InjectionPoint previousInjectionPoint = ConstructorResolver.setCurrentInjectionPoint(descriptor);
try {
Object shortcut = descriptor.resolveShortcut(this);
if (shortcut != null) {
return shortcut;
}
// @Value注解的注入
Class<?> type = descriptor.getDependencyType();
Object value = getAutowireCandidateResolver().getSuggestedValue(descriptor);
if (value != null) {
if (value instanceof String strValue) {
// 占位符解析
String resolvedValue = resolveEmbeddedValue(strValue);
BeanDefinition bd = (beanName != null && containsBean(beanName) ?
getMergedBeanDefinition(beanName) : null);
// EL表達式
value = evaluateBeanDefinitionString(resolvedValue, bd);
}
// 轉換類型
TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter());
try {
return converter.convertIfNecessary(value, type, descriptor.getTypeDescriptor());
}
catch (UnsupportedOperationException ex) {
// A custom TypeConverter which does not support TypeDescriptor resolution...
return (descriptor.getField() != null ?
converter.convertIfNecessary(value, type, descriptor.getField()) :
converter.convertIfNecessary(value, type, descriptor.getMethodParameter()));
}
}
//解析多個bean，例如List、set、Map
Object multipleBeans = resolveMultipleBeans(descriptor, beanName, autowiredBeanNames, typeConverter);
if (multipleBeans != null) {
return multipleBeans;
}
// 依賴查詢
Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor);
if (matchingBeans.isEmpty()) {
if (isRequired(descriptor)) {
raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);
}
return null;
}
String autowiredBeanName;
Object instanceCandidate;
// 如果有多個匹配的Bean，就根據(jù)方法名稱進行匹配
if (matchingBeans.size() > 1) {
autowiredBeanName = determineAutowireCandidate(matchingBeans, descriptor);
if (autowiredBeanName == null) {
if (isRequired(descriptor) || !indicatesMultipleBeans(type)) {
return descriptor.resolveNotUnique(descriptor.getResolvableType(), matchingBeans);
}
else {
// In case of an optional Collection/Map, silently ignore a non-unique case:
// possibly it was meant to be an empty collection of multiple regular beans
// (before 4.3 in particular when we didn't even look for collection beans).
return null;
}
}
instanceCandidate = matchingBeans.get(autowiredBeanName);
}
else {
// We have exactly one match.
Map.Entry<String, Object> entry = matchingBeans.entrySet().iterator().next();
autowiredBeanName = entry.getKey();
instanceCandidate = entry.getValue();
}
if (autowiredBeanNames != null) {
autowiredBeanNames.add(autowiredBeanName);
}
if (instanceCandidate instanceof Class) {
instanceCandidate = descriptor.resolveCandidate(autowiredBeanName, type, this);
}
Object result = instanceCandidate;
if (result instanceof NullBean) {
if (isRequired(descriptor)) {
raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);
}
result = null;
}
if (!ClassUtils.isAssignableValue(type, result)) {
throw new BeanNotOfRequiredTypeException(autowiredBeanName, type, instanceCandidate.getClass());
}
return result;
}
finally {
ConstructorResolver.setCurrentInjectionPoint(previousInjectionPoint);
}
}
到了這里，關于一起學SF框架系列5.4-模塊Beans-DefaultListableBeanFactory的文章就介紹完了。如果您還想了解更多內(nèi)容，請在右上角搜索TOY模板網(wǎng)以前的文章或繼續(xù)瀏覽下面的相關文章，希望大家以后多多支持TOY模板網(wǎng)！
