Spring實現HelloWord
前提：
1、已經在工程中定義了Spring配置文件beans.xml
2、寫好了一個測試類HelloWorld，里面有方法getMessage()用於輸出"hello world"。
3、在beans.xml中配置了一個類HelloWorld
示例代碼：
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
HelloWorld obj = (HelloWorld)context.getBean("HelloWorld");
obj.getMessage();
運行上面代碼，會在控制台打印出hello world字符。
Spring加載bean過程
注：分析基於spring-framework-4.3.8.RELEASE
ClassPathXmlApplicationContext的所有方法列表
構造函數調用了refresh方法
代碼new ClassPathXmlApplicationContext("beans.xml");使用了構造函數如下：
/**
* Create a new ClassPathXmlApplicationContext, loading the definitions
* from the given XML file and automatically refreshing the context.
* @param configLocation resource location
* @throws BeansException if context creation failed
*/
public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
this(new String[] {configLocation}, true, null);
}
/**
* Create a new ClassPathXmlApplicationContext with the given parent,
* loading the definitions from the given XML files.
* @param configLocations array of resource locations
* @param refresh whether to automatically refresh the context,
* loading all bean definitions and creating all singletons.
* Alternatively, call refresh manually after further configuring the context.
* @param parent the parent context
* @throws BeansException if context creation failed
* @see #refresh()
*/
public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
throws BeansException {
super(parent);
setConfigLocations(configLocations);
if (refresh) {
refresh();
}
}
上面構造方法調用了org.springframework.context.support.AbstractApplicationContext#refresh
@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.
//這里是實例化所有非懶加載的實例
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();
}
}
}
下面是調用構造器時，Spring初始化的主要過程。（refresh）
下面是refresh中的finishBeanFactoryInitialization(beanFactory);方法的主要過程。(AbstractApplicationContext.finishBeanFactoryInitialization())
下面是實例化Bean的過程：
（在新標簽打開查看大圖）
下面是加載Bean定義：AbstractXmlApplicationContext.loadBeanDefinitions()在refresh方法中的obtainFreshBeanFactory的bean定義階段。
調用關系如下：
加載Bean定義過程如下：
獲取bean流程分析
由於未設置HelloWorld類懶加載(lazy-init=true)(默認是non-lazy-load)，因此該類是在初始化ClassPathXmlApplicationContext ，即實例化。（參考：spring容器的懶加載lazy-init設置）
在調用getBean方法時，直接從緩存中拿到已經實例化的bean，詳細實現見下面源碼分析。
此外，bean實例化有優先級之分，原因是實現了BeanFactoryPostProcessor的接口在refresh方法執行invokeBeanFactoryPostProcessors(beanFactory);時就會實例化bean。
因為任何實現了BeanFactoryPostProcessor接口的bean首先要做的事就是先把自己實例化好。
1、調用的獲取bean的方法是org.springframework.context.support.AbstractApplicationContext#getBean(java.lang.Class<T>)，源碼如下：
@Override
public Object getBean(String name) throws BeansException {
assertBeanFactoryActive();
return getBeanFactory().getBean(name);
}
2、上面調用了org.springframework.context.support.AbstractApplicationContext#getBeanFactory方法
@Override
public abstract ConfigurableListableBeanFactory getBeanFactory() throws IllegalStateException;
該方法是個抽象方法，有兩個實現類
//GenericApplicationContext
private final DefaultListableBeanFactory beanFactory;
/**
* Return the single internal BeanFactory held by this context
* (as ConfigurableListableBeanFactory).
*/
@Override
public final ConfigurableListableBeanFactory getBeanFactory() {
return this.beanFactory;
}
//AbstractRefreshableApplicationContext
/** Bean factory for this context */
private DefaultListableBeanFactory beanFactory;
@Override
public final ConfigurableListableBeanFactory getBeanFactory() {
synchronized (this.beanFactoryMonitor) {
if (this.beanFactory == null) {
throw new IllegalStateException("BeanFactory not initialized or already closed - " +
"call 'refresh' before accessing beans via the ApplicationContext");
}
return this.beanFactory;
}
}
最終都是得到DefaultListableBeanFactory，因此調用的是org.springframework.beans.factory.support.DefaultListableBeanFactory#getBean(java.lang.Class<T>)方法，該方法又調用本類中的org.springframework.beans.factory.support.DefaultListableBeanFactory#getBean(java.lang.Class<T>, java.lang.Object...)方法。
@Override
public <T> T getBean(Class<T> requiredType) throws BeansException {
return getBean(requiredType, (Object[]) null);
}
@Override
public <T> T getBean(Class<T> requiredType, Object... args) throws BeansException {
NamedBeanHolder<T> namedBean = resolveNamedBean(requiredType, args);
if (namedBean != null) {
return namedBean.getBeanInstance();
}
BeanFactory parent = getParentBeanFactory();
if (parent != null) {
return parent.getBean(requiredType, args);
}
throw new NoSuchBeanDefinitionException(requiredType);
}
3、接着來看DefaultListableBeanFactory中的resolveNamedBean方法。
該方法從xml解析注冊到Spring容器中的bean中查找bean的聲名，看是否存在該名字的bean。
然后進行實例化，並返回。
@SuppressWarnings("unchecked")
private <T> NamedBeanHolder<T> resolveNamedBean(Class<T> requiredType, Object... args) throws BeansException {
Assert.notNull(requiredType, "Required type must not be null");
String[] candidateNames = getBeanNamesForType(requiredType);//查找候選的bean名稱
if (candidateNames.length > 1) { //如果有重名的需要進一步處理
List<String> autowireCandidates = new ArrayList<String>(candidateNames.length);
for (String beanName : candidateNames) {
if (!containsBeanDefinition(beanName) || getBeanDefinition(beanName).isAutowireCandidate()) {
autowireCandidates.add(beanName);
}
}
if (!autowireCandidates.isEmpty()) {
candidateNames = autowireCandidates.toArray(new String[autowireCandidates.size()]);
}
}
if (candidateNames.length == 1) {//如果只有一個，直接進行實例化
String beanName = candidateNames[0];
return new NamedBeanHolder<T>(beanName, getBean(beanName, requiredType, args));
}
else if (candidateNames.length > 1) { //如果有重名的需要進一步處理
Map<String, Object> candidates = new LinkedHashMap<String, Object>(candidateNames.length);
for (String beanName : candidateNames) {
if (containsSingleton(beanName)) {
candidates.put(beanName, getBean(beanName, requiredType, args));
}
else {
candidates.put(beanName, getType(beanName));
}
}
String candidateName = determinePrimaryCandidate(candidates, requiredType);
if (candidateName == null) {
candidateName = determineHighestPriorityCandidate(candidates, requiredType);
}
if (candidateName != null) {
Object beanInstance = candidates.get(candidateName);
if (beanInstance instanceof Class) {
beanInstance = getBean(candidateName, requiredType, args);
}
return new NamedBeanHolder<T>(candidateName, (T) beanInstance);
}
throw new NoUniqueBeanDefinitionException(requiredType, candidates.keySet());
}
return null;
}
bean的名稱存放在
/** List of bean definition names, in registration order */
private volatile List<String> beanDefinitionNames = new ArrayList<String>(256);
4、上面找到beanName之后調用org.springframework.beans.factory.support.AbstractBeanFactory#getBean(java.lang.String, java.lang.Class<T>, java.lang.Object...)實例化bean。
參考：
Spring源碼系列：依賴注入（一）（AbstractBeanFactory-getBean）
Spring的Bean-singleton模式
做一個合格的程序猿之淺析Spring IoC源碼（十一）Spring refresh()方法解析之一
doGetBean代碼的執行順序是：
1 首先先去實例化好的bean中去找，如果找到，直接返回
2 然后去當前beanfactory中父類factory找，如果能找到父類的factory，則叫父類去返回，（與jvm的classloader的雙親加載比較像~）
3 如果都沒有找到，則開始初次實例化，先標記開始實例化
4 開始查看當前要實例化的bean是否依賴於其他的bean，如果依賴，則先實例化依賴的bean，如果依賴的bean還依賴於其他的bean，則接着遞歸創建
5 如果創建的bean是單例（spring默認單例）接着創建
/**
* Return an instance, which may be shared or independent, of the specified bean.
* @param name the name of the bean to retrieve
* @param requiredType the required type of the bean to retrieve
* @param args arguments to use when creating a bean instance using explicit arguments
* (only applied when creating a new instance as opposed to retrieving an existing one)
* @return an instance of the bean
* @throws BeansException if the bean could not be created
*/
public <T> T getBean(String name, Class<T> requiredType, Object... args) throws BeansException {
return doGetBean(name, requiredType, args, false);
}
調用了
/**
* Return an instance, which may be shared or independent, of the specified bean.
* @param name the name of the bean to retrieve
* @param requiredType the required type of the bean to retrieve
* @param args arguments to use when creating a bean instance using explicit arguments
* (only applied when creating a new instance as opposed to retrieving an existing one)
* @param typeCheckOnly whether the instance is obtained for a type check,
* not for actual use
* @return an instance of the bean
* @throws BeansException if the bean could not be created
*/
@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.在已經實例化的bean的緩存中查找
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.可能是循環依賴了
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// Check if bean definition exists in this factory.檢查當前beanFactory是否有該實例
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.如果沒有，去父beanFactory實例化
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.
//如果該類有依賴的bean，先實例化依賴的bean
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
for (String dep : dependsOn) {
if (isDependent(beanName, dep)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
}
registerDependentBean(dep, beanName);
getBean(dep);
}
}
// Create bean instance.進行實例化
if (mbd.isSingleton()) {
//單例的bean在此處實例化
//此處調用org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#getSingleton(java.lang.String, org.springframework.beans.factory.ObjectFactory<?>)實例化
sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
@Override
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()) {//prototype類型的bean在這里實例化
// 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 name '" + scopeName + "'");
}
try {
Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
@Override
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;
}
5、上面調用了org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#getSingleton(java.lang.String, org.springframework.beans.factory.ObjectFactory<?>)對單例bean進行實例化，在該步由於bean已經在AbstractApplicationContext構造方法執行時調用refresh對非懶加載的bean已經實例化，因此這里直接從緩存singletonObjects中獲取bean實例並返回。下面的第6、7步是bean未實例化時進行實例化的主要流程（refresh實例化bean時也是調用這個流程）。
源碼如下：
/**
* Return the (raw) singleton object registered under the given name,
* creating and registering a new one if none registered yet.
* @param beanName the name of the bean
* @param singletonFactory the ObjectFactory to lazily create the singleton
* with, if necessary
* @return the registered singleton object
*/
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
Assert.notNull(beanName, "'beanName' must not be null");
synchronized (this.singletonObjects) {
Object singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
if (this.singletonsCurrentlyInDestruction) {
throw new BeanCreationNotAllowedException(beanName,
"Singleton bean creation not allowed while singletons of this factory are in destruction " +
"(Do not request a bean from a BeanFactory in a destroy method implementation!)");
}
if (logger.isDebugEnabled()) {
logger.debug("Creating shared instance of singleton bean '" + beanName + "'");
}
beforeSingletonCreation(beanName);
boolean newSingleton = false;
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
if (recordSuppressedExceptions) {
this.suppressedExceptions = new LinkedHashSet<Exception>();
}
try {
//此處的singletonFactory是傳入的new ObjectFactory<Object>()匿名類
singletonObject = singletonFactory.getObject();
newSingleton = true;
}
catch (IllegalStateException ex) {
// Has the singleton object implicitly appeared in the meantime ->
// if yes, proceed with it since the exception indicates that state.
singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
throw ex;
}
}
catch (BeanCreationException ex) {
if (recordSuppressedExceptions) {
for (Exception suppressedException : this.suppressedExceptions) {
ex.addRelatedCause(suppressedException);
}
}
throw ex;
}
finally {
if (recordSuppressedExceptions) {
this.suppressedExceptions = null;
}
afterSingletonCreation(beanName);
}
if (newSingleton) {
//如果是新的bean實例，添加到緩存singletonObjects中
addSingleton(beanName, singletonObject);
}
}
return (singletonObject != NULL_OBJECT ? singletonObject : null);
}
}
上面代碼中的匿名類是在第4步中傳入的，這里再次給出源碼：
sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
@Override
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;
}
}
});
所以實例化調用的是上面的getObject()方法。
添加到緩存的源碼如下。注意添加緩存后，在后續實例化bean前先在緩存中查找，如果存在直接返回實例化的bean。
如org.springframework.beans.factory.support.AbstractBeanFactory#doGetBean調用了org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#getSingleton(java.lang.String, boolean)來獲取緩存的bean實例。
org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#addSingleton
/**
* Add the given singleton object to the singleton cache of this factory.
* <p>To be called for eager registration of singletons.
* @param beanName the name of the bean
* @param singletonObject the singleton object
*/
protected void addSingleton(String beanName, Object singletonObject) {
synchronized (this.singletonObjects) {
this.singletonObjects.put(beanName, (singletonObject != null ? singletonObject : NULL_OBJECT));
this.singletonFactories.remove(beanName);
this.earlySingletonObjects.remove(beanName);
this.registeredSingletons.add(beanName);
}
}
6、這里調用了org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#createBean(java.lang.String, org.springframework.beans.factory.support.RootBeanDefinition, java.lang.Object[])方法實例化bean。
注：要查找createBean方法需要在DefaultListableBeanFactory類中查找，注意參數個數
/**
* Central method of this class: creates a bean instance,
* populates the bean instance, applies post-processors, etc.
* @see #doCreateBean
*/
@Override
protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {
if (logger.isDebugEnabled()) {
logger.debug("Creating instance of bean '" + beanName + "'");
}
RootBeanDefinition mbdToUse = mbd;
// Make sure bean class is actually resolved at this point, and
// clone the bean definition in case of a dynamically resolved Class
// which cannot be stored in the shared merged bean definition.
Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
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 {
// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
//如果實現了
Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
if (bean != null) {
return bean;
}
}
catch (Throwable ex) {
throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
"BeanPostProcessor before instantiation of bean failed", ex);
}
//進行實例化
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
if (logger.isDebugEnabled()) {
logger.debug("Finished creating instance of bean '" + beanName + "'");
}
return beanInstance;
}
7、上面調用了org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#doCreateBean實例化bean。根據注釋，該方法是Actually create the specified bean。
/**
* Actually create the specified bean. Pre-creation processing has already happened
* at this point, e.g. checking {@code postProcessBeforeInstantiation} callbacks.
* <p>Differentiates between default bean instantiation, use of a
* factory method, and autowiring a constructor.
* @param beanName the name of the bean
* @param mbd the merged bean definition for the bean
* @param args explicit arguments to use for constructor or factory method invocation
* @return a new instance of the bean
* @throws BeanCreationException if the bean could not be created
* @see #instantiateBean
* @see #instantiateUsingFactoryMethod
* @see #autowireConstructor
*/
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
throws BeanCreationException {
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
//1、使用合適的構造函數對bean進行實例化
// Create a new instance for the specified bean, using an appropriate instantiation strategy:
//factory method, constructor autowiring, or simple instantiation.
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
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.isDebugEnabled()) {
logger.debug("Eagerly caching bean '" + beanName +
"' to allow for resolving potential circular references");
}
addSingletonFactory(beanName, new ObjectFactory<Object>() {
@Override
public Object getObject() throws BeansException {
return getEarlyBeanReference(beanName, mbd, bean);
}
});
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
//2、這里進行bean初始化，設置屬性值
populateBean(beanName, mbd, instanceWrapper);
if (exposedObject != null) {
3、初始化
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<String>(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 " +
"'getBeanNamesOfType' 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;
}
三個關鍵方法源碼
使用構造器初始化bean
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#createBeanInstance
/**
* Create a new instance for the specified bean, using an appropriate instantiation strategy:
* factory method, constructor autowiring, or simple instantiation.
* @param beanName the name of the bean
* @param mbd the bean definition for the bean
* @param args explicit arguments to use for constructor or factory method invocation
* @return BeanWrapper for the new instance
* @see #instantiateUsingFactoryMethod
* @see #autowireConstructor
* @see #instantiateBean
*/
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, 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());
}
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);
}
}
// Need to determine the constructor...
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null ||
mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
return autowireConstructor(beanName, mbd, ctors, args);
}
// No special handling: simply use no-arg constructor.
return instantiateBean(beanName, mbd);
}
設置bean屬性
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#populateBean
/**
* Populate the bean instance in the given BeanWrapper with the property values
* from the bean definition.
* @param beanName the name of the bean
* @param mbd the bean definition for the bean
* @param bw BeanWrapper with bean instance
*/
protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
PropertyValues pvs = mbd.getPropertyValues();
if (bw == null) {
if (!pvs.isEmpty()) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
}
else {
// Skip property population phase for null instance.
return;
}
}
// Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
// state of the bean before properties are set. This can be used, for example,
// to support styles of field injection.
boolean continueWithPropertyPopulation = true;
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
continueWithPropertyPopulation = false;
break;
}
}
}
}
if (!continueWithPropertyPopulation) {
return;
}
if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
// Add property values based on autowire by name if applicable.
if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
autowireByName(beanName, mbd, bw, newPvs);
}
// Add property values based on autowire by type if applicable.
if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
autowireByType(beanName, mbd, bw, newPvs);
}
pvs = newPvs;
}
boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE);
if (hasInstAwareBpps || needsDepCheck) {
PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
if (hasInstAwareBpps) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvs == null) {
return;
}
}
}
}
if (needsDepCheck) {
checkDependencies(beanName, mbd, filteredPds, pvs);
}
}
applyPropertyValues(beanName, mbd, bw, pvs);
}
可以參考：Spring中獲取一個bean的流程-2
這里會在bean實例化時調用實現BeanPostProcessor的方法對bean進行處理。
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#initializeBean(java.lang.String, java.lang.Object, org.springframework.beans.factory.support.RootBeanDefinition)
/**
* Initialize the given bean instance, applying factory callbacks
* as well as init methods and bean post processors.
* <p>Called from {@link #createBean} for traditionally defined beans,
* and from {@link #initializeBean} for existing bean instances.
* @param beanName the bean name in the factory (for debugging purposes)
* @param bean the new bean instance we may need to initialize
* @param mbd the bean definition that the bean was created with
* (can also be {@code null}, if given an existing bean instance)
* @return the initialized bean instance (potentially wrapped)
* @see BeanNameAware
* @see BeanClassLoaderAware
* @see BeanFactoryAware
* @see #applyBeanPostProcessorsBeforeInitialization
* @see #invokeInitMethods
* @see #applyBeanPostProcessorsAfterInitialization
*/
protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged(new PrivilegedAction<Object>() {
@Override
public Object run() {
invokeAwareMethods(beanName, bean);
return null;
}
}, getAccessControlContext());
}
else {
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
//初始化
/**
* Give a bean a chance to react now all its properties are set,
* and a chance to know about its owning bean factory (this object).
* This means checking whether the bean implements InitializingBean or defines
* a custom init method, and invoking the necessary callback(s) if it does.
* @param beanName the bean name in the factory (for debugging purposes)
* @param bean the new bean instance we may need to initialize
* @param mbd the merged bean definition that the bean was created with
* (can also be {@code null}, if given an existing bean instance)
* @throws Throwable if thrown by init methods or by the invocation process
* @see #invokeCustomInitMethod
*/
protected void invokeInitMethods(String beanName, final Object bean, RootBeanDefinition mbd)
throws Throwable {
boolean isInitializingBean = (bean instanceof InitializingBean);
if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
if (logger.isDebugEnabled()) {
logger.debug("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
}
if (System.getSecurityManager() != null) {
try {
AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
@Override
public Object run() throws Exception {
((InitializingBean) bean).afterPropertiesSet();
return null;
}
}, getAccessControlContext());
}
catch (PrivilegedActionException pae) {
throw pae.getException();
}
}
else {
//InitializingBean接口方法調用
((InitializingBean) bean).afterPropertiesSet();
}
}
if (mbd != null) {
String initMethodName = mbd.getInitMethodName();
if (initMethodName != null && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
!mbd.isExternallyManagedInitMethod(initMethodName)) {
invokeCustomInitMethod(beanName, bean, mbd);
}
}
}
Spring初始化類實例
最后給出debug出來的Spring初始化bean的流程。
ServiceAuthToFujitsuClient.afterPropertiesSet() line: 109
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).invokeInitMethods(String, Object, RootBeanDefinition) line: 1367
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).initializeBean(String, Object, RootBeanDefinition) line: 1333
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).doCreateBean(String, RootBeanDefinition, Object[]) line: 471
AbstractAutowireCapableBeanFactory$1.run() line: 409
AccessController.doPrivileged(PrivilegedAction<T>, AccessControlContext) line: not available [native method]
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).createBean(String, RootBeanDefinition, Object[]) line: 380
AbstractBeanFactory$1.getObject() line: 264
DefaultListableBeanFactory(DefaultSingletonBeanRegistry).getSingleton(String, ObjectFactory) line: 220
DefaultListableBeanFactory(AbstractBeanFactory).doGetBean(String, Class, Object[], boolean) line: 261 -->此處實例化authorization的ref Client
DefaultListableBeanFactory(AbstractBeanFactory).getBean(String, Class, Object[]) line: 185
DefaultListableBeanFactory(AbstractBeanFactory).getBean(String) line: 164
BeanDefinitionValueResolver.resolveReference(Object, RuntimeBeanReference) line: 269
BeanDefinitionValueResolver.resolveValueIfNecessary(Object, Object) line: 104
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).applyPropertyValues(String, BeanDefinition, BeanWrapper, PropertyValues) line: 1244
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).populateBean(String, AbstractBeanDefinition, BeanWrapper) line: 1008
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).doCreateBean(String, RootBeanDefinition, Object[]) line: 470
AbstractAutowireCapableBeanFactory$1.run() line: 409
AccessController.doPrivileged(PrivilegedAction<T>, AccessControlContext) line: not available [native method]
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).createBean(String, RootBeanDefinition, Object[]) line: 380
AbstractBeanFactory$1.getObject() line: 264
DefaultListableBeanFactory(DefaultSingletonBeanRegistry).getSingleton(String, ObjectFactory) line: 220
DefaultListableBeanFactory(AbstractBeanFactory).doGetBean(String, Class, Object[], boolean) line: 261 --->此處實例化ServiceTarget的屬性authorization
DefaultListableBeanFactory(AbstractBeanFactory).getBean(String, Class, Object[]) line: 185
DefaultListableBeanFactory(AbstractBeanFactory).getBean(String) line: 164
BeanDefinitionValueResolver.resolveReference(Object, RuntimeBeanReference) line: 269
BeanDefinitionValueResolver.resolveValueIfNecessary(Object, Object) line: 104
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).applyPropertyValues(String, BeanDefinition, BeanWrapper, PropertyValues) line: 1244
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).populateBean(String, AbstractBeanDefinition, BeanWrapper) line: 1008
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).doCreateBean(String, RootBeanDefinition, Object[]) line: 470
AbstractAutowireCapableBeanFactory$1.run() line: 409
AccessController.doPrivileged(PrivilegedAction<T>, AccessControlContext) line: not available [native method]
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).createBean(String, RootBeanDefinition, Object[]) line: 380
AbstractBeanFactory$1.getObject() line: 264
DefaultListableBeanFactory(DefaultSingletonBeanRegistry).getSingleton(String, ObjectFactory) line: 220
DefaultListableBeanFactory(AbstractBeanFactory).doGetBean(String, Class, Object[], boolean) line: 261 --->此處實例化acsService的屬性acsServiceTarget
DefaultListableBeanFactory(AbstractBeanFactory).getBean(String, Class, Object[]) line: 185
DefaultListableBeanFactory(AbstractBeanFactory).getBean(String) line: 164
BeanDefinitionValueResolver.resolveReference(Object, RuntimeBeanReference) line: 269
BeanDefinitionValueResolver.resolveValueIfNecessary(Object, Object) line: 104
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).applyPropertyValues(String, BeanDefinition, BeanWrapper, PropertyValues) line: 1244
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).populateBean(String, AbstractBeanDefinition, BeanWrapper) line: 1008
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).doCreateBean(String, RootBeanDefinition, Object[]) line: 470
AbstractAutowireCapableBeanFactory$1.run() line: 409
AccessController.doPrivileged(PrivilegedAction<T>, AccessControlContext) line: not available [native method]
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).createBean(String, RootBeanDefinition, Object[]) line: 380
AbstractBeanFactory$1.getObject() line: 264
DefaultListableBeanFactory(DefaultSingletonBeanRegistry).getSingleton(String, ObjectFactory) line: 220
DefaultListableBeanFactory(AbstractBeanFactory).doGetBean(String, Class, Object[], boolean) line: 261 --->此處實例化acsService
DefaultListableBeanFactory(AbstractBeanFactory).getTypeForFactoryBean(String, RootBeanDefinition) line: 1198 調用了doGetBean
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).getTypeForFactoryBean(String, RootBeanDefinition) line: 625
DefaultListableBeanFactory(AbstractBeanFactory).isTypeMatch(String, Class) line: 450 --->此處如果是factorybean類型的，會對其進行實例化
mdb變量實時值：
Root bean: class [org.springframework.aop.framework.ProxyFactoryBean]; scope=singleton; abstract=false; lazyInit=false; autowireMode=0; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=null; factoryMethodName=null; initMethodName=null; destroyMethodName=null; defined in class path resource [acs-basic.xml]
beanName為acsService
// Check bean class whether we're dealing with a FactoryBean.
if (FactoryBean.class.isAssignableFrom(beanClass)) {
if (!BeanFactoryUtils.isFactoryDereference(name)) {
// If it's a FactoryBean, we want to look at what it creates, not the factory class.
Class type = getTypeForFactoryBean(beanName, mbd);
return (type != null && typeToMatch.isAssignableFrom(type));
}
else {
return typeToMatch.isAssignableFrom(beanClass);
}
}
DefaultListableBeanFactory.getBeanNamesForType(Class, boolean, boolean) line: 223 此處會校驗所有bean(包括FactoryBean)
DefaultListableBeanFactory.getBeansOfType(Class, boolean, boolean) line: 303
DefaultListableBeanFactory.getBeansOfType(Class) line: 297
ConverterFacade.afterPropertiesSet() line: 85
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).invokeInitMethods(String, Object, RootBeanDefinition) line: 1367
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).initializeBean(String, Object, RootBeanDefinition) line: 1333
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).doCreateBean(String, RootBeanDefinition, Object[]) line: 471
AbstractAutowireCapableBeanFactory$1.run() line: 409
AccessController.doPrivileged(PrivilegedAction<T>, AccessControlContext) line: not available [native method]
DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).createBean(String, RootBeanDefinition, Object[]) line: 380
AbstractBeanFactory$1.getObject() line: 264
DefaultListableBeanFactory(DefaultSingletonBeanRegistry).getSingleton(String, ObjectFactory) line: 220
DefaultListableBeanFactory(AbstractBeanFactory).doGetBean(String, Class, Object[], boolean) line: 261
DefaultListableBeanFactory(AbstractBeanFactory).getBean(String, Class, Object[]) line: 185
DefaultListableBeanFactory(AbstractBeanFactory).getBean(String) line: 164
DMCXmlWebApplicationContext(AbstractApplicationContext).getBean(String) line: 881
DMCXmlWebApplicationContext(AbstractApplicationContext).invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory) line: 534 --->實例化所有實現BeanFactoryPostProcessor的類，此處包括以下類，此時遍歷到ConverterFacade#0
--->[com.huawei.xtvmw.commons.config.ConfigAssembler, org.springframework.beans.factory.config.PropertyPlaceholderConfigurer, com.huawei.xtvmw.commons.rmi.interceptor.RemoteInvocationClassFactory#0, com.huawei.xtvmw.commons.rmi.ServiceInterceptorFactory#0, com.huawei.xtvmw.repository.spi.ConverterFacade#0, adjustSpider, org.springframework.beans.factory.config.CustomEditorConfigurer#0]
DMCXmlWebApplicationContext(AbstractApplicationContext).refresh() line: 363
ContextLoader.createWebApplicationContext(ServletContext, ApplicationContext) line: 255
ContextLoader.initWebApplicationContext(ServletContext) line: 199
DMCContextLoaderServlet(ContextLoaderServlet).init() line: 81
DMCContextLoaderServlet.init() line: 48
DMCContextLoaderServlet(GenericServlet).init(ServletConfig) line: 160
StandardWrapper.initServlet(Servlet) line: 1280
StandardWrapper.loadServlet() line: 1193
StandardWrapper.load() line: 1088
StandardContext.loadOnStartup(Container[]) line: 5033
StandardContext.startInternal() line: 5317
StandardContext(LifecycleBase).start() line: 150
ContainerBase$StartChild.call() line: 1517
ContainerBase$StartChild.call() line: 1508
FutureTask$Sync.innerRun() line: 303
FutureTask<V>.run() line: 138
ThreadPoolExecutor$Worker.runTask(Runnable) line: 886
ThreadPoolExecutor$Worker.run() line: 908
Thread.run() line: 662
總結
上面對Spring實例化bean的流程做了簡單分析，有幾個地方需要注意：
1、使用ClassPathXmlApplicationContext時，會調用refresh方法對所有非懶加載的bean實例化（默認），此后再調用getBean方法會直接從緩存獲取
2、如果設置bean為懶加載，則bean在調用getBean等方法時才會實例化
3、BeanFactoryPostProcessor的實例化的優先級最高
4、beanPostProcessor是可以臨時修改bean的，它的優先級高於正常實例化bean的，如果beanPostProcessor能返回，則直接返回了
5、由2、3兩點可以知道bean的實例化是有優先級的