前面分析了bean解析的过程,知道了bean都是以beandefinition的形式放在bean factory里面的。下面来看一下bean具体的获取过程。
Spring 提供了一个获取bean的工具方法:
WebApplicationContextUtils.getRequiredWebApplicationContext(ServletContext sc).getBean(String beanName);
OK,稍微追踪了一下代码,发现着落在了AbstraceBeanFactory下面:
- public Object getBean(String name) throws BeansException {
- return doGetBean(name, null, null, false);
- }
- private <T> T doGetBean(
- final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
- throws BeansException {
- final String beanName = transformedBeanName(name);
- Object bean;
- // Eagerly check singleton cache for manually registered singletons.
- Object sharedInstance = getSingleton(beanName);
- if (sharedInstance != null && args == null) {
- if (logger.isDebugEnabled()) {
- if (isSingletonCurrentlyInCreation(beanName)) {
- logger.debug(“Returning eagerly cached instance of singleton bean ‘” + beanName +
- “‘ that is not fully initialized yet – a consequence of a circular reference”);
- }
- else {
- logger.debug(“Returning cached instance of singleton bean ‘” + beanName + “‘”);
- }
- }
- bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
- }
- else {
- // Fail if we’re already creating this bean instance:
- // We’re assumably within a circular reference.
- if (isPrototypeCurrentlyInCreation(beanName)) {
- throw new BeanCurrentlyInCreationException(beanName);
- }
- // Check if bean definition exists in this factory.
- BeanFactory parentBeanFactory = getParentBeanFactory();
- if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
- // Not found -> check parent.
- String nameToLookup = originalBeanName(name);
- if (args != null) {
- // Delegation to parent with explicit args.
- return (T) parentBeanFactory.getBean(nameToLookup, args);
- }
- else {
- // No args -> delegate to standard getBean method.
- return parentBeanFactory.getBean(nameToLookup, requiredType);
- }
- }
- if (!typeCheckOnly) {
- markBeanAsCreated(beanName);
- }
- final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
- checkMergedBeanDefinition(mbd, beanName, args);
- // Guarantee initialization of beans that the current bean depends on.
- String[] dependsOn = mbd.getDependsOn();
- if (dependsOn != null) {
- for (String dependsOnBean : dependsOn) {
- getBean(dependsOnBean);
- registerDependentBean(dependsOnBean, beanName);
- }
- }
- // Create bean instance.
- if (mbd.isSingleton()) {
- sharedInstance = getSingleton(beanName, new ObjectFactory() {
- public Object getObject() throws BeansException {
- try {
- return createBean(beanName, mbd, args);
- }
- catch (BeansException ex) {
- // Explicitly remove instance from singleton cache: It might have been put there
- // eagerly by the creation process, to allow for circular reference resolution.
- // Also remove any beans that received a temporary reference to the bean.
- destroySingleton(beanName);
- throw ex;
- }
- }
- });
- bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
- }
- else if (mbd.isPrototype()) {
- // It’s a prototype -> create a new instance.
- Object prototypeInstance = null;
- try {
- beforePrototypeCreation(beanName);
- prototypeInstance = createBean(beanName, mbd, args);
- }
- finally {
- afterPrototypeCreation(beanName);
- }
- bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
- }
- else {
- String scopeName = mbd.getScope();
- final Scope scope = this.scopes.get(scopeName);
- if (scope == null) {
- throw new IllegalStateException(“No Scope registered for scope ‘” + scopeName + “‘”);
- }
- try {
- Object scopedInstance = scope.get(beanName, new ObjectFactory() {
- 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);
- }
- }
- }
- // Check if required type matches the type of the actual bean instance.
- if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
- throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
- }
- return (T) bean;
- }
doGetBean….呃,好长的方法。慢慢研究一下。
Object sharedInstance = getSingleton(beanName);
这个方法首先去已经缓存了的Singleton里面寻找,如果没有,就到手工注入的singleton缓存里面寻找,如果没有,
再到缓存的FactoryBean类型的singleton里面寻找,如果还没有…继续doGetBean里面的下一步。
接下来如果当前beanfactory有parent,就到parentBeanFactory里面寻找,如果找不到,继续…
接下来就是获取spring里面当初解析出来的bean模板:RootBeanDefinition。然后
在当前factory下面注册一下依赖关系,下面就到了关键的步骤了,根据bean是singleton还是Prototype或者其他什么scope类型来分别定义bean的获取过程。下面以singleton为例来进行分析。
注意一下代码:
- if (mbd.isSingleton()) {
- sharedInstance = getSingleton(beanName, new ObjectFactory() {
- 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);
- }
可见bean的生成委托给了createBean(name,mdb,args)方法。
这个方法的实现是在子类AbstractAutowireCapableBeanFactory里面。
- protected Object createBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
- throws BeanCreationException {
- if (logger.isDebugEnabled()) {
- logger.debug(“Creating instance of bean ‘” + beanName + “‘”);
- }
- // Make sure bean class is actually resolved at this point.
- resolveBeanClass(mbd, beanName);
- // Prepare method overrides.
- try {
- mbd.prepareMethodOverrides();
- }
- catch (BeanDefinitionValidationException ex) {
- throw new BeanDefinitionStoreException(mbd.getResourceDescription(),
- beanName, “Validation of method overrides failed”, ex);
- }
- try {
- // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
- Object bean = resolveBeforeInstantiation(beanName, mbd);
- if (bean != null) {
- return bean;
- }
- }
- catch (Throwable ex) {
- throw new BeanCreationException(mbd.getResourceDescription(), beanName,
- “BeanPostProcessor before instantiation of bean failed”, ex);
- }
- Object beanInstance = doCreateBean(beanName, mbd, args);
- if (logger.isDebugEnabled()) {
- logger.debug(“Finished creating instance of bean ‘” + beanName + “‘”);
- }
- return beanInstance;
- }
从上面的代码可以看出,先调用了resolveBeforeInstantiation方法。如果返回一个非空对象,那么就直接返回这个对象。 于是分析一下这个方法:
- protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
- Object bean = null;
- if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
- // Make sure bean class is actually resolved at this point.
- if (mbd.hasBeanClass() && !mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
- bean = applyBeanPostProcessorsBeforeInstantiation(mbd.getBeanClass(), beanName);
- if (bean != null) {
- bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
- }
- }
- mbd.beforeInstantiationResolved = (bean != null);
- }
- return bean;
- }
是不是似曾相识哪?那就对了 ! Aop的实现的核心啊,回想一下AbstractAutoProxyCreator,就是实现了InstantiationAwareBeanPostProcessor接口。从AbstractAutoProxyCreator的postProcessBeforeInstantiation代码可以很容易的看出,如果bean需要代理,那么返回一个代理类,否则返回Null.
结合当前代码,那就是如果产生了代理类,那么试着调用beanpostprocessors的postProcessAfterInitialization方法,然后返回这个代理类。从这里也可以看出,如果被代理的类定义了postProcessBeforeInitialization,init等方法,将根本没有调用的机会! 所以被代理类在实现BeanPostProcessor,InitilizingBean等接口时要非常小心。否则可能发现有些方法根本没有回调。
当然了,不一定非要产生代理类,也有可能有其他的实现了InstantiationAwareBeanPostProcessor接口的类也返回非空,这里就不详细分析。我大致看了一下,至少我看的几个实现了InstantiationAwareBeanPostProcessor接口的类是返回null的,除了AbstractAutoProxyCreator.
下面继续。如果调用InstantiationAwareBeanPostProcessor后依然返回Null,那么就继续下面的步骤,也就是激动人心的bean的instantiation过程了!这里是调用了doCreateBean(beanName, mbd, args)方法:
- protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {
- // Instantiate the bean.
- BeanWrapper instanceWrapper = null;
- if (mbd.isSingleton()) {
- 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);
- // Allow post-processors to modify the merged bean definition.
- synchronized (mbd.postProcessingLock) {
- if (!mbd.postProcessed) {
- applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
- 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() {
- public Object getObject() throws BeansException {
- return getEarlyBeanReference(beanName, mbd, bean);
- }
- });
- }
- // Initialize the bean instance.
- Object exposedObject = bean;
- try {
- populateBean(beanName, mbd, instanceWrapper);
- if (exposedObject != null) {
- 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;
- }
汗~又是一个长方法。慢慢分析。
这个方法大致分为这么几步:
1. 产生一个beanwrapper.
2. 调用实现了MergedBeanDefinitionPostProcessors接口的类
3. populateBean
4. 初始化bean
5. 注册产生的bean
下面分别就前几个步骤进行分析。
1. 产生beanwrapper
- 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…
- if (mbd.resolvedConstructorOrFactoryMethod != null && args == null) {
- if (mbd.constructorArgumentsResolved) {
- 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);
- }
在这里可以看出,如果为bean定义了factoryMehtod或者constructor,那么将分别根据factoryMethod或construcgtor完成bean的初始化。否则调用如下方法:
- protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {
- try {
- Object beanInstance;
- final BeanFactory parent = this;
- if (System.getSecurityManager() != null) {
- beanInstance = AccessController.doPrivileged(new PrivilegedAction<Object>() {
- public Object run() {
- return getInstantiationStrategy().instantiate(mbd, beanName, parent);
- }
- }, getAccessControlContext());
- }
- else {
- beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);
- }
- BeanWrapper bw = new BeanWrapperImpl(beanInstance);
- initBeanWrapper(bw);
- return bw;
- }
- catch (Throwable ex) {
- throw new BeanCreationException(mbd.getResourceDescription(), beanName, “Instantiation of bean failed”, ex);
- }
- }
这里有一个InstantiationStrategy接口,这个接口定了bean初始化的策略。比如在
当前类AbstractAutowireCapableBeanFactory下面一开始就定义了一个变量:
- private InstantiationStrategy instantiationStrategy = new CglibSubclassingInstantiationStrategy();
可见,默认的初始化策略是CglibSubclassingInstantiationStrategy。
这个策略的特殊之处就在于如果bean需要有method injection,那么就通过cglib代理的方式产生原本的bean class的一个子类从而实现method override.
OK,至此BeanWrapper的生成基本清晰了。
下面就是实现了MergedBeanDefinitionPostProcessors的类的调用了。这个接口的具体意思我还不是很清楚。稍后研究一下补全。
然后就是populateBean. 这个方法就是把BeanDefinition里面维护的bean的属性populate到beanwrapper里面。
接下来就是bean的初始化:
if (exposedObject != null) {
exposedObject = initializeBean(beanName, exposedObject, mbd);
了解bean的初始化流程还是蛮有意义的:
- protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
- if (System.getSecurityManager() != null) {
- AccessController.doPrivileged(new PrivilegedAction<Object>() {
- 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;
- }
可见初始化顺序是: XXAware接口的实现->postProcessBeforeInitialization->InitializingBean的afterPropertiesSet-> custom Init方法->postProcessAfterInitialization
OK.这就是bean初始化的顺序啦!
最后当然就是bean的注册了!
- protected void registerDisposableBeanIfNecessary(String beanName, Object bean, RootBeanDefinition mbd) {
- AccessControlContext acc = (System.getSecurityManager() != null ? getAccessControlContext() : null);
- if (!mbd.isPrototype() && requiresDestruction(bean, mbd)) {
- if (mbd.isSingleton()) {
- // Register a DisposableBean implementation that performs all destruction
- // work for the given bean: DestructionAwareBeanPostProcessors,
- // DisposableBean interface, custom destroy method.
- registerDisposableBean(beanName,
- new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
- }
- else {
- // A bean with a custom scope…
- Scope scope = this.scopes.get(mbd.getScope());
- if (scope == null) {
- throw new IllegalStateException(“No Scope registered for scope ‘” + mbd.getScope() + “‘”);
- }
- scope.registerDestructionCallback(beanName,
- new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
- }
- }
- }
这里面涉及到了bean以及与scope相关的生命周期的管理,需要单独分析一下。下篇文章再分析。