ApplicationContext容器的設計
程式設計式使用 ioc
ioc
- 建立
ioc
io
bean
Resource
- 建立一個
BeanFactory
bean
- 建立一個載入
BeanDefinition
XmlBeanDefinitionReader
BeanFactory
- 使用讀取器将
Resource
bean
BeanFactory
ioc容器的初始化過程
ioc
容器的初始化是由
refresh()
方法來啟動的。
bean
定義的載入和依賴注入是兩個獨立的過程。在
ioc
容器初始化階段并沒有進行依賴注入，如果通過設定
lazyinit
屬性（非懶加載的），可以讓
bean
在
ioc
容器初始化的時候就預先完成。
FileSystemXmlApplicationContext：
兩個功能：
- 對執行個體化應用上下文的支援。主要展現在
refresh()
- 讀取檔案系統中以
xml
BeanDefinition
通過protected Resource getResourceByPath(String path) { if (path.startsWith("/")) { path = path.substring(1); } return new FileSystemResource(path); }getResourceByPath(Stirng)
Resource
Resource定位
由
ResourceLoader
通過統一的
Resource
接口來完成。
AbstractApplicationContext
通過繼承基類
DefaultResourceLoader
來擷取
Resource
。 getResourceByPath(String)方法的調用：
FileSystemXmlApplicationContext
的構造方法：
public FileSystemXmlApplicationContext(
String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
throws BeansException {
super(parent);
setConfigLocations(configLocations);
if (refresh) {
refresh(); //<1>
}
}
refresh()
<1>
調用
refresh()
方法：
//AbstractApplicationContext#refresh
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// 準備重新整理容器的上下文.
prepareRefresh();
// 告訴AbstractRefreshableApplicationContext去重新整理BeanFactory 調用refreshBeanFactory方法.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // <1>
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// 設定BeanFactory的後置處理器.postProcessBeanFactory(beanFactory);
postProcessBeanFactory(beanFactory);
// 調用BeanFactory的後置處理器，這些後置處理器是在Bean定義中向容器注冊的.
invokeBeanFactoryPostProcessors(beanFactory);
// 注冊Bean的後置處理器，在Bean的建立過程中調用.
registerBeanPostProcessors(beanFactory);
// 對上下文消息進行初始化.
initMessageSource();
// 初始化上下文事件機制.
initApplicationEventMulticaster();
// 初始化其他的特殊的Bean.
onRefresh();
// 檢查監聽Bean并且将這些Bean向容器注冊.
registerListeners();
// 執行個體化所有的（no-lazy-init）單件.
finishBeanFactoryInitialization(beanFactory);
// 釋出容器事件，結束Refresh過程.
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();
}
}
}
在
<1>
調用
obtainFreshBeanFactory()
方法對
BeanFactory
進行初始化。
// AbstractApplicationContext#obtainFreshBeanFactory
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
refreshBeanFactory(); // <1>
return getBeanFactory();
}
refreshBeanFactory()
在
<1>
中調用
refreshBeanFactory()
進行初始化
BeanFactory
。
//AbstractRefreshableApplicationContext#refreshBeanFactory
protected final void refreshBeanFactory() throws BeansException {
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory();
}
try {
DefaultListableBeanFactory beanFactory = createBeanFactory(); // <1>
beanFactory.setSerializationId(getId());
customizeBeanFactory(beanFactory);
loadBeanDefinitions(beanFactory); // <2>
this.beanFactory = beanFactory;
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
//AbstractRefreshableApplicationContext#createBeanFactory
protected DefaultListableBeanFactory createBeanFactory() {
return new DefaultListableBeanFactory(getInternalParentBeanFactory());
}
//AbstractXmlApplicationContext#loadBeanDefinitions(DefaultListableBeanFactory)
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory); //<3>
// Configure the bean definition reader with this context's
// resource loading environment.
beanDefinitionReader.setEnvironment(this.getEnvironment());
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
// Allow a subclass to provide custom initialization of the reader,
// then proceed with actually loading the bean definitions.
initBeanDefinitionReader(beanDefinitionReader);
loadBeanDefinitions(beanDefinitionReader); // <4>
}
<1>
建立了一個
DefaultListableBeanFactory
作為基本的
ioc
容器，如果在之前已經存在
BeanFactory
，那麼會将之前的銷毀清除。
<2>
加載
BeanDefinition
。·
<3>
建立讀取器
BeanDefinitionReader
。模闆方法，将其實作交給不同的子類，這樣就會對不同的
Resource
建立不同的讀取器。
<4>
通過建立的
BeanDefinitionReader
來加載
BeanDefiniton
。
loadBeanDefinitions方法
//AbstractXmlApplicationContext#loadBeanDefinitions(XmlBeanDefinitionReader)
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
// 以Resource的方式獲得配置檔案的資源位置
Resource[] configResources = getConfigResources();
if (configResources != null) {
reader.loadBeanDefinitions(configResources);
}
// 以String的方式擷取配置檔案的資源位置
String[] configLocations = getConfigLocations();
if (configLocations != null) {
reader.loadBeanDefinitions(configLocations); // <1>
}
}
BeanDefinitionReader
在
<1>
調用
AbstractBeanDefinitionReader#loadBeanDefinitions(String...)
對所有的
Resource
所在位置進行周遊。會調用
DefaultResourceLoader#getResource
擷取
Resource
，通過
getResource(String)
方法調用
FileSystemXmlApplicationContext#getResourceByPath
傳回
Resource
。至此完成定位。
getResource(String)
// org.springframework.core.io.DefaultResourceLoader#getResource
public Resource getResource(String location) {
Assert.notNull(location, "Location must not be null");
for (ProtocolResolver protocolResolver : getProtocolResolvers()) {
Resource resource = protocolResolver.resolve(location, this);
if (resource != null) {
return resource;
}
}
if (location.startsWith("/")) {
return getResourceByPath(location);
}
else if (location.startsWith(CLASSPATH_URL_PREFIX)) { // 處理classpth:辨別路徑
return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()), getClassLoader());
}
else {
try {
// Try to parse the location as a URL...
URL url = new URL(location); // 處理url辨別路徑
return (ResourceUtils.isFileURL(url) ? new FileUrlResource(url) : new UrlResource(url));
}
catch (MalformedURLException ex) {
// No URL -> resolve as resource path.
return getResourceByPath(location);
}
}
}
載入和解析
把定義好的
bean
轉換成
ioc
内部的資料結構
BeanDefinition
，友善我們對
bean
進行管理和依賴注入的實作。
在資源定位的過程中已經得到
Resource
，接下來需要使用
BeanDefinitionReader
通過周遊
Resource
來完成對
BeanDefinition
的載入。
// AbstractBeanDefinitionReader#loadBeanDefinitions(Resource...)
public int loadBeanDefinitions(Resource... resources) throws BeanDefinitionStoreException {
Assert.notNull(resources, "Resource array must not be null");
int count = 0;
for (Resource resource : resources) {
count += loadBeanDefinitions(resource); // <1>
}
return count;
}
<1>
是調用
AbstractBeanDefinitionReader
的實作類的
loadBeanDefinitions(Resource)
方法來對
BeanDefinition
進行加載。
// XmlBeanDefinitionReader#loadBeanDefinitions(Resource)
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
return loadBeanDefinitions(new EncodedResource(resource)); // 調用對EncodedResource載入
}
// XmlBeanDefinitionReader#loadBeanDefinitions(EncodedResource)
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
Assert.notNull(encodedResource, "EncodedResource must not be null");
if (logger.isTraceEnabled()) {
logger.trace("Loading XML bean definitions from " + encodedResource);
}
Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
if (!currentResources.add(encodedResource)) {
throw new BeanDefinitionStoreException(
"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
}
try (InputStream inputStream = encodedResource.getResource().getInputStream()) {
InputSource inputSource = new InputSource(inputStream); // <1> 得到io的InputSource準備進行讀取
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
return doLoadBeanDefinitions(inputSource, encodedResource.getResource()); // <2>
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"IOException parsing XML document from " + encodedResource.getResource(), ex);
}
finally {
currentResources.remove(encodedResource);
if (currentResources.isEmpty()) {
this.resourcesCurrentlyBeingLoaded.remove();
}
}
}
<2>
實際上是從特定的
Resource
中加載
BeanDefinition
的地方。
// XmlBeanDefinitionReader#doLoadBeanDefinitions
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
Document doc = doLoadDocument(inputSource, resource); //<1>
int count = registerBeanDefinitions(doc, resource); //<2>
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + count + " bean definitions from " + resource);
}
return count;
}
catch (BeanDefinitionStoreException ex) {
throw ex;
}
}
<1>
通過
DocumentLoader
對
xml
檔案進行解析得到
Document
對象。
<2>
使用
BeanDefinitionDocumentReader#registerBeanDefinitions
對
Document
進行解析，其中又使用了
BeanDefinitionParserDelegate#parseCustomElement(Element)
對
Document
文檔樹進行解析，将
BeanDefinition
封裝在
BeanDefinitionHolder
中，還包含
beanName
和
aliases
。
注冊
向
ioc
注冊
BeanDefinition
。通過
BeanDefinitionRegistry
接口實作完成。
BeanDefinition
在
ioc
容器中存儲的資料機構是
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(256);
在載入和解析的時候已經将對
bean
的配置封裝到
BeanDefinitionHolder
中，接下來調用
registerBeanDefinition()
方法将
BeanDefinition
注冊到
ioc
容器中。
registerBeanDefinition()
// AbstractBeanDefinitionParser#registerBeanDefinition
// BeanDefinitionReaderUtils#registerBeanDefinition
public static void registerBeanDefinition(
BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {
// Register bean definition under primary name.
String beanName = definitionHolder.getBeanName();
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition()); // <1>
// Register aliases for bean name, if any.
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String alias : aliases) {
registry.registerAlias(beanName, alias);
}
}
}
<1>
如果
beanName
已經存在并且
isAllowBeanDefinitionOverriding
，那麼會覆寫之前的
BeanDefinition
。否則将
beanName
添加到
beanDefinitionNames
中，通過
BeanDefinition
作為
value
和
beanName
作為
key
注冊到
beanDefinitionMap
中去。
// DefaultListableBeanFactory#registerBeanDefinition
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
throws BeanDefinitionStoreException {
Assert.hasText(beanName, "Bean name must not be empty");
Assert.notNull(beanDefinition, "BeanDefinition must not be null");
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
if (existingDefinition != null) {
if (!isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
}
else if (existingDefinition.getRole() < beanDefinition.getRole()) {
// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
if (logger.isInfoEnabled()) {
logger.info("Overriding user-defined bean definition for bean '" + beanName +
"' with a framework-generated bean definition: replacing [" +
existingDefinition + "] with [" + beanDefinition + "]");
}
}
else if (!beanDefinition.equals(existingDefinition)) {
if (logger.isDebugEnabled()) {
logger.debug("Overriding bean definition for bean '" + beanName +
"' with a different definition: replacing [" + existingDefinition +
"] with [" + beanDefinition + "]");
}
}
else {
if (logger.isTraceEnabled()) {
logger.trace("Overriding bean definition for bean '" + beanName +
"' with an equivalent definition: replacing [" + existingDefinition +
"] with [" + beanDefinition + "]");
}
}
this.beanDefinitionMap.put(beanName, beanDefinition);
}
else {
if (hasBeanCreationStarted()) {
// Cannot modify startup-time collection elements anymore (for stable iteration)
synchronized (this.beanDefinitionMap) {
this.beanDefinitionMap.put(beanName, beanDefinition);
List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
removeManualSingletonName(beanName);
}
}
else {
// Still in startup registration phase
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
removeManualSingletonName(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if (existingDefinition != null || containsSingleton(beanName)) {
resetBeanDefinition(beanName);
}
else if (isConfigurationFrozen()) {
clearByTypeCache();
}
}
ioc容器的依賴注入
引導建立Bean
如果是單例對象，即未設定
lazyinit
屬性會在
BeanDefinition
加載和注冊的時候就進行建立，否在第一次使用
bean
的時候，通過
AbstractBeanFactory
的
getBean
方法來建立
bean
。
getBean方法—doGetBean方法
// org.springframework.beans.factory.support.AbstractBeanFactory#getBean(java.lang.String, java.lang.Class<T>, java.lang.Object...)
public <T> T getBean(String name, @Nullable Class<T> requiredType, @Nullable Object... args)
throws BeansException {
return doGetBean(name, requiredType, args, false);
}
// org.springframework.beans.factory.support.AbstractBeanFactory#doGetBean
protected <T> T doGetBean(
String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)
throws BeansException {
String beanName = transformedBeanName(name);
Object bean;
// Eagerly check singleton cache for manually registered singletons.
Object sharedInstance = getSingleton(beanName); // <1>
if (sharedInstance != null && args == null) {
if (logger.isTraceEnabled()) {
if (isSingletonCurrentlyInCreation(beanName)) {
logger.trace("Returning eagerly cached instance of singleton bean '" + beanName +
"' that is not fully initialized yet - a consequence of a circular reference");
}
else {
logger.trace("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)) { // <2>
// Not found -> check parent.
String nameToLookup = originalBeanName(name);
if (parentBeanFactory instanceof AbstractBeanFactory) {
return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
nameToLookup, requiredType, args, typeCheckOnly);
}
else if (args != null) {
// Delegation to parent with explicit args.
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else if (requiredType != null) {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
else {
return (T) parentBeanFactory.getBean(nameToLookup);
}
}
if (!typeCheckOnly) {
markBeanAsCreated(beanName);
}
try {
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 dep : dependsOn) { // <3>
if (isDependent(beanName, dep)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
}
registerDependentBean(dep, beanName); // <4>
try {
getBean(dep); //<5>
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
}
}
}
// Create bean instance.
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, () -> {
try {
return createBean(beanName, mbd, args); // <5>
}
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); // <6>
}
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();
if (!StringUtils.hasLength(scopeName)) {
throw new IllegalStateException("No scope name defined for bean ´" + beanName + "'");
}
Scope scope = this.scopes.get(scopeName);
if (scope == null) {
throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
}
try {
Object scopedInstance = scope.get(beanName, () -> {
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 && !requiredType.isInstance(bean)) {
try {
T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
if (convertedBean == null) {
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
return convertedBean;
}
catch (TypeMismatchException ex) {
if (logger.isTraceEnabled()) {
logger.trace("Failed to convert bean '" + name + "' to required type '" +
ClassUtils.getQualifiedName(requiredType) + "'", ex);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
return (T) bean;
}
<1>
從目前的
BeanFactory
中擷取
bean
，如果取得可能需要通過
getObjectForBeanInstance
來對
FactoryBean
進行處理。
bean
未加載，則通過目前的
BeanFactory
或父級
BeanFactory
來尋找
BeanDefinition
來進行初始化
bean
。
<3>
對
@DependsOn
注解标注的屬性進行判斷是否産生循環依賴，如果沒有産生循環依賴，
<4>
将
dependentBeanName
和
beanName
關系存儲到
dependentBeanMap
（B被A依賴-> k-v）和
dependenciesForBeanMap
（A依賴B->k-v）中。最後
<5>
建立
bean
。
createBean
方法最終在
getSingletion
方法中調用
ObjectFactory
的
getObject
方法中觸發調用。
createBean方法—doCreateBean方法
// AbstractAutowireCapableBeanFactory#createBean(String, RootBeanDefinition, Object[])
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
if (logger.isTraceEnabled()) {
logger.trace("Creating instance of bean '" + beanName + "'");
}
RootBeanDefinition mbdToUse = mbd;
// 判斷這個bean是否可以被執行個體化
Class<?> resolvedClass = resolveBeanClass(mbd, beanName); // <1>
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
mbdToUse = new RootBeanDefinition(mbd);
mbdToUse.setBeanClass(resolvedClass);
}
// Prepare method overrides.
try {
mbdToUse.prepareMethodOverrides();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
beanName, "Validation of method overrides failed", ex);
}
try {
// 如果bean配置了後置處理器，則會傳回一個代理對象代替目标對象.
Object bean = resolveBeforeInstantiation(beanName, mbdToUse); // <2>
if (bean != null) {
return bean;
}
}
catch (Throwable ex) {
throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
"BeanPostProcessor before instantiation of bean failed", ex);
}
try {
Object beanInstance = doCreateBean(beanName, mbdToUse, args); // <3>
if (logger.isTraceEnabled()) {
logger.trace("Finished creating instance of bean '" + beanName + "'");
}
return beanInstance;
}
catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
// A previously detected exception with proper bean creation context already,
// or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
throw ex;
}
catch (Throwable ex) {
throw new BeanCreationException(
mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
}
}
<1>
判斷這個bean是否可以被執行個體化，
<2>
如果bean配置了後置處理器，則會傳回一個代理對象代替目标對象，
<3>
調用
doCreateBean
是真正建立
bean
的方法。
// AbstractAutowireCapableBeanFactory#doCreateBean
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
// BeanWrapper是用來持有建立的bean的.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) { // 如果是單例清除在factoryBeanInstanceCache中的緩存
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
instanceWrapper = createBeanInstance(beanName, mbd, args); // <1>
}
Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
// Allow post-processors to modify the merged bean definition.
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Post-processing of merged bean definition failed", ex);
}
mbd.postProcessed = true;
}
}
// Eagerly cache singletons to be able to resolve circular references
// even when triggered by lifecycle interfaces like BeanFactoryAware.
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
isSingletonCurrentlyInCreation(beanName));
if (earlySingletonExposure) {
if (logger.isTraceEnabled()) {
logger.trace("Eagerly caching bean '" + beanName +
"' to allow for resolving potential circular references");
}
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
Object exposedObject = bean; // <2>
try {
populateBean(beanName, mbd, instanceWrapper);
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
catch (Throwable ex) {
if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
throw (BeanCreationException) ex;
}
else {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
}
}
if (earlySingletonExposure) {
Object earlySingletonReference = getSingleton(beanName, false);
if (earlySingletonReference != null) {
if (exposedObject == bean) {
exposedObject = earlySingletonReference;
}
else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
String[] dependentBeans = getDependentBeans(beanName);
Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
for (String dependentBean : dependentBeans) {
if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
actualDependentBeans.add(dependentBean);
}
}
if (!actualDependentBeans.isEmpty()) {
throw new BeanCurrentlyInCreationException(beanName,
"Bean with name '" + beanName + "' has been injected into other beans [" +
StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
"] in its raw version as part of a circular reference, but has eventually been " +
"wrapped. This means that said other beans do not use the final version of the " +
"bean. This is often the result of over-eager type matching - consider using " +
"'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.");
}
}
}
}
// Register bean as disposable.
try {
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}
return exposedObject;
}
<1> createBeanInstance
建立最普通的
java
對象，可以通過
BeanDefinition
的
Supplier
、工廠方法
instantiateUsingFactoryMethod
、自動裝配構造函數
autowireConstructor
、預設的構造函數
instantiateBean
。
createBeanInstance方法
// AbstractAutowireCapableBeanFactory#createBeanInstance
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
// Make sure bean class is actually resolved at this point.
Class<?> beanClass = resolveBeanClass(mbd, beanName);
if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
}
Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
if (instanceSupplier != null) {
return obtainFromSupplier(instanceSupplier, beanName);
}
if (mbd.getFactoryMethodName() != null) {
return instantiateUsingFactoryMethod(beanName, mbd, args);
}
// Shortcut when re-creating the same bean...
boolean resolved = false;
boolean autowireNecessary = false;
if (args == null) {
synchronized (mbd.constructorArgumentLock) {
if (mbd.resolvedConstructorOrFactoryMethod != null) {
resolved = true;
autowireNecessary = mbd.constructorArgumentsResolved;
}
}
}
if (resolved) {
if (autowireNecessary) {
return autowireConstructor(beanName, mbd, null, null);
}
else {
return instantiateBean(beanName, mbd);
}
}
// Candidate constructors for autowiring?
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
return autowireConstructor(beanName, mbd, ctors, args);
}
// Preferred constructors for default construction?
ctors = mbd.getPreferredConstructors();
if (ctors != null) {
return autowireConstructor(beanName, mbd, ctors, null);
}
// No special handling: simply use no-arg constructor.
return instantiateBean(beanName, mbd);
}
在最常用的
instantiateBean
方法中，主要使用
SimpleInstantiationStrategy
的
instantiate
方法來建立對象。主要有
cglib
和反射兩種建立對象的形式。
instantiateBean方法
// AbstractAutowireCapableBeanFactory#instantiateBean
protected BeanWrapper instantiateBean(String beanName, RootBeanDefinition mbd) {
try {
Object beanInstance;
if (System.getSecurityManager() != null) {
beanInstance = AccessController.doPrivileged(
(PrivilegedAction<Object>) () -> getInstantiationStrategy().instantiate(mbd, beanName, this),
getAccessControlContext());
}
else {
beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, this);
}
BeanWrapper bw = new BeanWrapperImpl(beanInstance);
initBeanWrapper(bw);
return bw;
}
catch (Throwable ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex);
}
}
// SimpleInstantiationStrategy#instantiate(RootBeanDefinition, String, BeanFactory)
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {
// Don't override the class with CGLIB if no overrides.
if (!bd.hasMethodOverrides()) {
Constructor<?> constructorToUse;
synchronized (bd.constructorArgumentLock) {
constructorToUse = (Constructor<?>) bd.resolvedConstructorOrFactoryMethod;
if (constructorToUse == null) {
final Class<?> clazz = bd.getBeanClass();
if (clazz.isInterface()) {
throw new BeanInstantiationException(clazz, "Specified class is an interface");
}
try {
if (System.getSecurityManager() != null) {
constructorToUse = AccessController.doPrivileged(
(PrivilegedExceptionAction<Constructor<?>>) clazz::getDeclaredConstructor);
}
else {
constructorToUse = clazz.getDeclaredConstructor();
}
bd.resolvedConstructorOrFactoryMethod = constructorToUse;
}
catch (Throwable ex) {
throw new BeanInstantiationException(clazz, "No default constructor found", ex);
}
}
}
return BeanUtils.instantiateClass(constructorToUse); // <1>
}
else {
// Must generate CGLIB subclass.
return instantiateWithMethodInjection(bd, beanName, owner); //<2>
}
}
如果沒有
look-up
和
replaced-method
（實作
MethodReplacer
接口）方法
<1>
最終通過反射
constructor.newInstance
來建立對象，否則
<2>
最終通過
cglib
建立代理的對象。
- 反射
// BeanUtils#instantiateClass(=Constructor<T>,Object...) public static <T> T instantiateClass(Constructor<T> ctor, Object... args) throws BeanInstantiationException { Assert.notNull(ctor, "Constructor must not be null"); try { ReflectionUtils.makeAccessible(ctor); if (KotlinDetector.isKotlinReflectPresent() && KotlinDetector.isKotlinType(ctor.getDeclaringClass())) { return KotlinDelegate.instantiateClass(ctor, args); } else { Class<?>[] parameterTypes = ctor.getParameterTypes(); Assert.isTrue(args.length <= parameterTypes.length, "Can't specify more arguments than constructor parameters"); Object[] argsWithDefaultValues = new Object[args.length]; for (int i = 0 ; i < args.length; i++) { if (args[i] == null) { Class<?> parameterType = parameterTypes[i]; argsWithDefaultValues[i] = (parameterType.isPrimitive() ? DEFAULT_TYPE_VALUES.get(parameterType) : null); } else { argsWithDefaultValues[i] = args[i]; } } return ctor.newInstance(argsWithDefaultValues); } } catch (InstantiationException ex) { throw new BeanInstantiationException(ctor, "Is it an abstract class?", ex); } catch (IllegalAccessException ex) { throw new BeanInstantiationException(ctor, "Is the constructor accessible?", ex); } catch (IllegalArgumentException ex) { throw new BeanInstantiationException(ctor, "Illegal arguments for constructor", ex); } catch (InvocationTargetException ex) { throw new BeanInstantiationException(ctor, "Constructor threw exception", ex.getTargetException()); } } -
cglib
建立類的位元組碼檔案
createEnhancedSubclass
subClass
// CglibSubclassingInstantiationStrategy.CglibSubclassCreator#instantiate public Object instantiate(@Nullable Constructor<?> ctor, Object... args) { Class<?> subclass = createEnhancedSubclass(this.beanDefinition); Object instance; if (ctor == null) { instance = BeanUtils.instantiateClass(subclass); } else { try { Constructor<?> enhancedSubclassConstructor = subclass.getConstructor(ctor.getParameterTypes()); instance = enhancedSubclassConstructor.newInstance(args); } catch (Exception ex) { throw new BeanInstantiationException(this.beanDefinition.getBeanClass(), "Failed to invoke constructor for CGLIB enhanced subclass [" + subclass.getName() + "]", ex); } } // SPR-10785: set callbacks directly on the instance instead of in the // enhanced class (via the Enhancer) in order to avoid memory leaks. Factory factory = (Factory) instance; factory.setCallbacks(new Callback[] {NoOp.INSTANCE, new LookupOverrideMethodInterceptor(this.beanDefinition, this.owner), new ReplaceOverrideMethodInterceptor(this.beanDefinition, this.owner)}); return instance; // CglibSubclassingInstantiationStrategy.CglibSubclassCreator#createEnhancedSubclass private Class<?> createEnhancedSubclass(RootBeanDefinition beanDefinition) { Enhancer enhancer = new Enhancer(); enhancer.setSuperclass(beanDefinition.getBeanClass()); enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE); if (this.owner instanceof ConfigurableBeanFactory) { ClassLoader cl = ((ConfigurableBeanFactory) this.owner).getBeanClassLoader(); enhancer.setStrategy(new ClassLoaderAwareGeneratorStrategy(cl)); } enhancer.setCallbackFilter(new MethodOverrideCallbackFilter(beanDefinition)); enhancer.setCallbackTypes(CALLBACK_TYPES); return enhancer.createClass(); }
依賴注入
在
doCreateBean
建立完成基本的對象之後，
populateBean
方法來進行屬性的依賴注入。
populateBean方法
// AbstractAutowireCapableBeanFactory#populateBean
protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
if (bw == null) {
if (mbd.hasPropertyValues()) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
}
else {
// Skip property population phase for null instance.
return;
}
}
// <1>
// 在注入properties屬性之前，可以通過後置處理器的postProcessAfterInstantiation方法
// 向bean（除spring應用之外的bean）注入一些字段進行指派。
// 比如：@Autoware
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
return;
}
}
}
}
// 從beanDefinition中獲得所有property屬性
PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);
int resolvedAutowireMode = mbd.getResolvedAutowireMode();
// <1> 對autoware進行處理
if (resolvedAutowireMode == AUTOWIRE_BY_NAME || resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
// Add property values based on autowire by name if applicable.
if (resolvedAutowireMode == AUTOWIRE_BY_NAME) {
autowireByName(beanName, mbd, bw, newPvs);
}
// Add property values based on autowire by type if applicable.
if (resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
autowireByType(beanName, mbd, bw, newPvs);
}
pvs = newPvs;
}
boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE);
PropertyDescriptor[] filteredPds = null;
if (hasInstAwareBpps) {
if (pvs == null) {
pvs = mbd.getPropertyValues();
}
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
// <2>
// 使用postProcessProperties方法對PropertyValue進行後置處理
PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
return;
}
}
pvs = pvsToUse;
}
}
}
if (needsDepCheck) {
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
checkDependencies(beanName, mbd, filteredPds, pvs);
}
if (pvs != null) {
// <3>
// 對屬性進行注入
applyPropertyValues(beanName, mbd, bw, pvs);
}
}
在
<1>
和
<2>
中使用到的後置處理器的方法并不相同，
<1>
中使用的方法為在建立
beanWrapper
之後調用，中間會對
@Autowared
注解的屬性進行處理。而
<2>
執行次序在
<1>
和對
autoware
配置處理之後進行。
<3>
是完成對
PropertyValue
最終注入的步驟，雖然在此之前可能已經完成部分屬性的注入。
applyPropertyValues方法
// AbstractAutowireCapableBeanFactory#applyPropertyValues
protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
if (pvs.isEmpty()) {
return;
}
if (System.getSecurityManager() != null && bw instanceof BeanWrapperImpl) {
((BeanWrapperImpl) bw).setSecurityContext(getAccessControlContext());
}
MutablePropertyValues mpvs = null;
List<PropertyValue> original;
// <1>
// 得到PropertyValue集合
if (pvs instanceof MutablePropertyValues) {
mpvs = (MutablePropertyValues) pvs;
if (mpvs.isConverted()) {
// Shortcut: use the pre-converted values as-is.
try {
bw.setPropertyValues(mpvs);
return;
}
catch (BeansException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Error setting property values", ex);
}
}
original = mpvs.getPropertyValueList();
}
else {
original = Arrays.asList(pvs.getPropertyValues());
}
TypeConverter converter = getCustomTypeConverter();
if (converter == null) {
converter = bw;
}
// <2>
// 使用valueResolver對PropertyValue進行解析，将解析後的PropertyValue（深拷貝）放到
// List集合中，成功解析後的PropertyValue使用setPropertyValues對屬性進行設定
BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);
// Create a deep copy, resolving any references for values.
List<PropertyValue> deepCopy = new ArrayList<>(original.size());
boolean resolveNecessary = false;
for (PropertyValue pv : original) {
if (pv.isConverted()) {
deepCopy.add(pv);
}
else {
String propertyName = pv.getName();
Object originalValue = pv.getValue();
if (originalValue == AutowiredPropertyMarker.INSTANCE) {
Method writeMethod = bw.getPropertyDescriptor(propertyName).getWriteMethod();
if (writeMethod == null) {
throw new IllegalArgumentException("Autowire marker for property without write method: " + pv);
}
originalValue = new DependencyDescriptor(new MethodParameter(writeMethod, 0), true);
}
Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
Object convertedValue = resolvedValue;
boolean convertible = bw.isWritableProperty(propertyName) &&
!PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
if (convertible) {
convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);
}
// Possibly store converted value in merged bean definition,
// in order to avoid re-conversion for every created bean instance.
if (resolvedValue == originalValue) {
if (convertible) {
pv.setConvertedValue(convertedValue);
}
deepCopy.add(pv);
}
else if (convertible && originalValue instanceof TypedStringValue &&
!((TypedStringValue) originalValue).isDynamic() &&
!(convertedValue instanceof Collection || ObjectUtils.isArray(convertedValue))) {
pv.setConvertedValue(convertedValue);
deepCopy.add(pv);
}
else {
resolveNecessary = true;
deepCopy.add(new PropertyValue(pv, convertedValue));
}
}
}
if (mpvs != null && !resolveNecessary) {
mpvs.setConverted();
}
// <3>
// Set our (possibly massaged) deep copy.
try {
bw.setPropertyValues(new MutablePropertyValues(deepCopy));
}
catch (BeansException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Error setting property values", ex);
}
}
在
<2>
的
valueResolver
進行解析的時候，會從
BeanFactory
中去擷取要注入到屬性中的
bean
，是以會觸發其他
bean
的初始化和依賴注入過程。
setPropertyValues
方法将屬性進行注入到
bean
中。
setPropertyValues
方法會使用反射擷取
get
方法将解析得到的屬性設定到相應的地方。
lazy-init屬性和執行個體化
在
ioc
容器的初始化過程中，
bean
的依賴注入和執行個體化有兩種情況。一種是非懶加載的單執行個體
bean
，會在容器初始化
refresh
中的
finishBeanFactoryInitialization
方法中進行依賴注入和執行個體化。另一種是懶加載的單執行個體
bean
和多執行個體
bean
，會在第一次使用
bean
的時候調用
getBean
方法完成
bean
的依賴注入和執行個體化。
// AbstractApplicationContext#finishBeanFactoryInitialization
// 完成容器的初始化，完成對（非懶加載）單執行個體bean的初始化
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// Initialize conversion service for this context.
if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
beanFactory.setConversionService(
beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
}
// Register a default embedded value resolver if no bean post-processor
// (such as a PropertyPlaceholderConfigurer bean) registered any before:
// at this point, primarily for resolution in annotation attribute values.
if (!beanFactory.hasEmbeddedValueResolver()) {
beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
}
// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {
getBean(weaverAwareName);
}
// Stop using the temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(null);
// Allow for caching all bean definition metadata, not expecting further changes.
beanFactory.freezeConfiguration();
// <1> 執行個體化非懶加載的bean
// Instantiate all remaining (non-lazy-init) singletons.
beanFactory.preInstantiateSingletons();
}
// DefaultListableBeanFactory#preInstantiateSingletons
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...
// <1>
for (String beanName : beanNames) {
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
if (isFactoryBean(beanName)) {
Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
if (bean instanceof FactoryBean) {
FactoryBean<?> factory = (FactoryBean<?>) bean;
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged(
(PrivilegedAction<Boolean>) ((SmartFactoryBean<?>) factory)::isEagerInit,
getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
}
else {
getBean(beanName);
}
}
}
// 擷取到所有的BeanDefinition然後周遊将非懶加載的單執行個體bean使用getBean方法進行初始化
// Trigger post-initialization callback for all applicable beans...
for (String beanName : beanNames) {
Object singletonInstance = getSingleton(beanName);
if (singletonInstance instanceof SmartInitializingSingleton) {
SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
smartSingleton.afterSingletonsInstantiated();
return null;
}, getAccessControlContext());
}
else {
smartSingleton.afterSingletonsInstantiated();
}
}
}
}
值得注意的地方是在擷取所有的
BeanDefinition
的
name
之後，周遊檢查是否使用
getBean
進行執行個體化。如果這個
bean
是一個
FactoryBean
，那麼會在原本的
beanName
之前添加一個
&
代表是
FactoryBean
本身。
然後進行檢查
SmartFactoryBean
的
isEagerInit
檢視是否滿足能夠提前注冊該
FactoryBean
所産生的對象，而通過
getObject
方法建立的
bean
的
beanName
就是沒有
&
的。否則在
getBean(factoryBeanName)
時才能初始化
getObject
方法建立的
bean
。
FactoryBean的實作
在引導建立
bean
調用方法
doGetBean
的過程中，首先
getSingleton
（檢查已經執行個體化的單例，并且還允許對目前建立的單例的提前引用，解析循環引用），然後使用
getObjectForBeanInstance
通過檢視
name
是否有
&
，如果有
&
說明擷取的是
FactoryBean
本身，直接傳回即可，否則使用
FactoryBean.getObject
建立。我們在
singletonObjects
中是根據
benaName
（無
&
）存放的
FactoryBean
（在使用
getSingleton
方法的時候是使用的
String beanName = transformedBeanName(name)
），而
FactoryBean
建立的單例對象通過
factoryBeanObjectCache
來緩存起來。
// AbstractBeanFactory#getObjectForBeanInstance
protected Object getObjectForBeanInstance(
// beanInstance 是用來建立對象的FactoryBean
Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) {
// <1>
// 檢查是否是帶有"&"擷取 FactoryBean本身
if (BeanFactoryUtils.isFactoryDereference(name)) {
if (beanInstance instanceof NullBean) {
return beanInstance;
}
if (!(beanInstance instanceof FactoryBean)) {
throw new BeanIsNotAFactoryException(beanName, beanInstance.getClass());
}
if (mbd != null) {
mbd.isFactoryBean = true;
}
return beanInstance;
}
if (!(beanInstance instanceof FactoryBean)) {
return beanInstance;
}
Object object = null;
if (mbd != null) {
mbd.isFactoryBean = true;
}
else {
// 從緩存中擷取bean
// 這個bean是單執行個體bean在FactoryBean第一次通過getObject方法建立的時候設定的
object = getCachedObjectForFactoryBean(beanName);
}
if (object == null) {
FactoryBean<?> factory = (FactoryBean<?>) beanInstance;
if (mbd == null && containsBeanDefinition(beanName)) {
mbd = getMergedLocalBeanDefinition(beanName);
}
boolean synthetic = (mbd != null && mbd.isSynthetic());
// <1>
// 在getObjectFromFactoryBean方法中使用doGetObjectFromFactoryBean調用
// getObject方法建立bean
object = getObjectFromFactoryBean(factory, beanName, !synthetic);
}
return object;
}
// FactoryBeanRegistrySupport#getObjectFromFactoryBean
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);
Object alreadyThere = this.factoryBeanObjectCache.get(beanName);
if (alreadyThere != null) {
object = alreadyThere;
}
// 使用後置處理器進行處理
else {
if (shouldPostProcess) {
if (isSingletonCurrentlyInCreation(beanName)) {
return object;
}
beforeSingletonCreation(beanName);
try {
object = postProcessObjectFromFactoryBean(object, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(beanName,
"Post-processing of FactoryBean's singleton object failed", ex);
}
finally {
afterSingletonCreation(beanName);
}
}
if (containsSingleton(beanName)) {
// 将通過FactoryBean建立的bean設定到緩存中
this.factoryBeanObjectCache.put(beanName, object);
}
}
}
return object;
}
}
else {
Object object = doGetObjectFromFactoryBean(factory, beanName);
if (shouldPostProcess) {
try {
object = postProcessObjectFromFactoryBean(object, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "Post-processing of FactoryBean's object failed", ex);
}
}
return object;
}
}
// FactoryBeanRegistrySupport#doGetObjectFromFactoryBean
private Object doGetObjectFromFactoryBean(FactoryBean<?> factory, String beanName) throws BeanCreationException {
Object object;
try {
if (System.getSecurityManager() != null) {
AccessControlContext acc = getAccessControlContext();
try {
object = AccessController.doPrivileged((PrivilegedExceptionAction<Object>) factory::getObject, acc);
}
catch (PrivilegedActionException pae) {
throw pae.getException();
}
}
else {
object = factory.getObject(); // 建立bean
}
}
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) {
if (isSingletonCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(
beanName, "FactoryBean which is currently in creation returned null from getObject");
}
object = new NullBean();
}
return object;
}
總結
IOC容器完整加載過程(XML)
// |--1.new FileSystemXmlApplicationContext(String... configLocations)
// 觸發了AbstractApplicationContext#refresh方法
// |--2.AbstractApplicationContext#obtainFreshBeanFactory初始化IOC容器（DefaultListableBeanFactory）
// |----AbstractRefreshableApplicationContext#refreshBeanFactory得到了BeanFactory
// |----AbstractRefreshableApplicationContext#loadBeanDefinitions加載并初始化BeanDefinition
// 對BeanFactory進行準備環境設定
// |----調用BeanFactoryPostProcessor的postProcessBeanDefinitionRegistry，對BeanFactory進行後置處理
// |----注冊BeanPostProcessor
// |--3.BeanDefinition資源的加載
// XmlBeanDefinitionReader在進行解析之前，DefaultResourceLoader調用getResource，
// 間接調用FileSystemXmlApplicationContext的getResourceByPath得到Resource
// |--4.BeanDefinition資源的解析
// 通過DefaultDocumentLoader将Resource加載為Document，對XML中的元素進行解析
// |--5.BeanDefinition的注冊
// 使用BeanDefinitionParserDelegate将XML中的元素解析為BeanDefinition所需要的樣子，
// 最後将BeanDefinition，beanName，alias封裝到BeanDefinitionHolder中，
// 将BeanDefinitionHolder添加到beanDefinitionMap
// |--6.AbstractApplicationContext#finishBeanFactoryInitialization完成對no-lazy-init單執行個體bean進行初始化
// 選擇no-lazy-init單執行個體的BeanDefinition
// |----ConfigurableListableBeanFactory#preInstantiateSingletons
// |------将bean加載到容器中來
// FactoryBean：getBean("&"+beanName); 判斷是否滿足調用getObject方法建立bean
// 普通：getBean(beanName)
// |----調用SmartInitializingSingleton#afterSingletonsInstantiated
// 對SmartInitializingSingleton接口bean進行處理
// |--7.DefaultSingletonBeanRegistry#getSingleton(String)從容器中擷取單執行個體bean （循環依賴）
// 1):從有已經建立好的singletonObjects中擷取
// 2):1)中沒有擷取到，建立的bean的set集合singletonsCurrentlyInCreation包括該bean，
// 就從earlySingletonObjects中擷取bean
// 3):2)中未擷取到，從singletonFactories中擷取到ObjectFactory，通過getObject方法建立bean，
// 并将其設定到earlySingletonObjects中，将ObjectFactory從singletonFactories中移除
// 如果傳回非空并且不需要顯式參數：傳回結果處于正在建立期間得到的就是不完整的bean，否則得到的是一個單執行個體bean的緩存
// 傳回結果為null，則建立bean
// |--8.建立bean
// 1)從目前BeanFactory及父BeanFactory中得到BeanDefinition
// 進行depend-on的循環依賴檢查和注冊，并調用getBean先執行個體化depend-on的bean
// |----單執行個體：DefaultSingletonBeanRegistry#getSingleton(String,ObjectFactory<?>)
// 從singletonObjects中嘗試擷取，成功直接傳回
// |------1.1)beforeSingletonCreation(beanName);
// 将建立的beanName設定到singletonsCurrentlyInCreation正在建立的bean的set集合中
// |------1.2)調用ObjectFactory的getObject方法，觸發 createBean方法建立bean
// |--------AbstractAutowireCapableBeanFactory#resolveBeforeInstantiation方法給使用InstantiationAwareBeanPostProcessor傳回一個proxy的機會
/**
Class<?> targetType = determineTargetType(beanName, mbd);
if (targetType != null) {
bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
if (bean != null) {
bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
}
}
**/
// |--------AbstractAutowireCapableBeanFactory#createBeanInstance,
// 建立BeanWrapper，建立了普通的java執行個體，
// 通過如果沒有override方法就用java反射，否則用cglib
// |------1.3)在建立普通的java執行個體之後，接下來是考慮對循環依賴的解決方案提前暴露
/**
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
isSingletonCurrentlyInCreation(beanName));
if (earlySingletonExposure) {
if (logger.isTraceEnabled()) {
logger.trace("Eagerly caching bean '" + beanName +
"' to allow for resolving potential circular references");
}
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
/**
addSingletonFactory向singletonFactories中添加ObjectFactory,
其中getObject方法中回調getEarlyBeanReference，
調用SmartInstantiationAwareBeanPostProcessor對bean進行處理
// |------1.4)屬性注入（會觸發其他bean的getBean進入建立和注入屬性循環）
// 1.4.1)利用InstantiationAwareBeanPostProcessor的postProcessAfterInstantiation，
// 向bean注入一些屬性，比如@Autowired
// 1.4.2)根據自動注入的name或type來對屬性進行注入
// 1.4.3)利用InstantiationAwareBeanPostProcessor的postProcessProperties，進行處理
// 1.4.4)AbstractAutowireCapableBeanFactory#applyPropertyValues，
對所有的ProperrtyValue使用BeanDefinitionValueResolver進行解析，
在解析的過程中會觸發其他bean的執行個體化，
并将解析後的PropertyValue放到list集合中，然後周遊使用set方法設定到屬性上去
// |------1.5)AbstractAutowireCapableBeanFactory#initializeBean(String, Object, RootBeanDefinition)對bean的初始化
1.5.1)invokeAwareMethods對Aware類型的bean進行設定
1.5.2)後置處理器的postProcessBeforeInitialization方法執行
1.5.3)invokeInitMethods方法首先對InitializingBean調用接口的afterPropertiesSet方法
然後通過反射執行init-method
1.5.4)後置處理器的postProcessAfterInitialization方法執行
1.5.5)對比目前的bean和提前暴露獲得的bean進行更新
// |------1.6)AbstractBeanFactory#getObjectForBeanInstance對FactoryBean進行處理，如果是&則直接傳回，
否則使用FactoryBean的getObject方法建立bean，
并根據isSingleton方法決定是否将其設定到factoryBeanObjects緩存中，以便下一次注入的是同一個對象
// |------1.7)afterSingletonCreation方法将beanName從singletonsCurrentlyInCreation中删除
// |------1.8)addSingleton，将最終的執行個體添加到IOC容器的singletonObjects中，然後對緩存進行清理。
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