bean的创建第一部分

Posted 2021-02-09 honger

AbstractBeanFactory.doGetBean

protected <T> T doGetBean(
            final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
            throws BeansException {
//转换beanName，应为有可能是别名
        final String beanName = transformedBeanName(name);
        Object bean;

        // Eagerly check singleton cache for manually registered singletons.
//从缓存获取单例对象
        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 + "‘");
                }
            }
//如果是BeanFactory，那么需要通过getObject方法获取真正的对象
            bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
        }

        else {
            // Fail if we‘re already creating this bean instance:
            // We‘re assumably within a circular reference.
//如果是多例的，通过ThreadLocal判断是否循环引用，如果是直接报错
            if (isPrototypeCurrentlyInCreation(beanName)) {
                throw new BeanCurrentlyInCreationException(beanName);
            }

            // Check if bean definition exists in this factory.
            BeanFactory parentBeanFactory = getParentBeanFactory();
//如果有父容器，并且当前容器不存在beanName，才会从父容器中寻找
            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);
                }
            }
//如果不是仅仅进行类型检查，那么将这个beanName存入alreadyCreated这个set集合，标记它已经创建或即将创建，并且从mergedBeanDefinitions map集合中移除
            if (!typeCheckOnly) {
                markBeanAsCreated(beanName);
            }

            try {
//合并beanDefinition，如果有父子级，那么 就会把父beanDefinition的属性合并到一起，最后变成RootBeanDefinition
                final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
                //如果这个RootBeanDefinition是抽象的，那么就直接抛错
checkMergedBeanDefinition(mbd, beanName, args);

                // Guarantee initialization of beans that the current bean depends on.
                //如果在xml中配置了当前bean依赖其他的bean，如果发现这种依赖被循环，直接抛错，比如a   ->   b c d  然后  c - a f y,当spring发现c依赖a f y之后，就去创建a，然后发现a已经c这个依赖了，那么就报错，这种通过xml配置的依赖，可能是注入依赖，也有可能是必须某个bean先创建的依赖（就像是ant里的某个任务依赖另一个任务，这种是不允许早期依赖的）
String[] dependsOn = mbd.getDependsOn();
                if (dependsOn != null) {
                    for (String dependsOnBean : dependsOn) {
                        if (isDependent(beanName, dependsOnBean)) {
                            throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                                    "Circular depends-on relationship between ‘" + beanName + "‘ and ‘" + dependsOnBean + "‘");
                        }
//注册依赖bean，这里主要注册了两个集合，dependentBeanMap  beanName -> 依赖的beanName集合， dependenciesForBeanMap   依赖的beanName -》 beanName集合
                        registerDependentBean(dependsOnBean, beanName);
//先创建依赖的bean，想象一下，如果循环依赖，就会一直递归调用下去，直至stackOverflow。
                        getBean(dependsOnBean);
                    }
                }

                // Create bean instance.
                if (mbd.isSingleton()) {
                    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;
                            }
                        }
                    });
//如果是工厂bean，那么就使用工厂来创建这个bean
                    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 {
//使用其他的scope创建bean
                    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. 转换成指定bean类型
        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;
    }


SimpleAliasRegistry.canonicalName

public String canonicalName(String name) {
        String canonicalName = name;
        // Handle aliasing...
        String resolvedName;
        do {
 //获取最终的beanName
            resolvedName = this.aliasMap.get(canonicalName);
            if (resolvedName != null) {
                canonicalName = resolvedName;
            }
        }
        while (resolvedName != null);
        return canonicalName;
    }


DefaultSingletonBeanRegistry.getSingleton

protected Object getSingleton(String beanName, boolean allowEarlyReference) {
//从singletonObjects map中获取已经创建好的单例对象
        Object singletonObject = this.singletonObjects.get(beanName);
        if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
            synchronized (this.singletonObjects) {
//获取提前暴露的bean工厂，这个bean工厂获取到的bean是还没有初始化完成的bean
                singletonObject = this.earlySingletonObjects.get(beanName);
                if (singletonObject == null && allowEarlyReference) {
                    ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
                    if (singletonFactory != null) {
//获取还没有进行设置属性，未初始化，未被后置处理器处理的原始bean
                        singletonObject = singletonFactory.getObject();
//将未被初始化完全的bean扔到容器中，用于循环依赖
                        this.earlySingletonObjects.put(beanName, singletonObject);
//未初始化提前暴露的工厂使用完后就移除它
                        this.singletonFactories.remove(beanName);
                    }
                }
            }
        }
        return (singletonObject != NULL_OBJECT ? singletonObject : null);
    }


AbstractBeanFactory.getObjectForBeanInstance

protected Object getObjectForBeanInstance(
            Object beanInstance, String name, String beanName, RootBeanDefinition mbd) {

        // Don‘t let calling code try to dereference the factory if the bean isn‘t a factory.
//如果name是以&开头的，并且beanInstance又不是FactoryBean就抛出错误
        if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {
            throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());
        }

        // Now we have the bean instance, which may be a normal bean or a FactoryBean.
        // If it‘s a FactoryBean, we use it to create a bean instance, unless the
        // caller actually wants a reference to the factory.
//如果这个bean不是工厂或者这个name是以&开头的，那么直接返回bean
//不是工厂bean，那么就说明它已经是想要的bean了，如果是以&开头的，并且前面已经通过了这个bean是工厂bean的校验，那么就说明用户想要获取这个工厂bean
        if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
            return beanInstance;
        }

        Object object = null;
//mbd在获取早期未初始化bean的时候为null，这个时候会从工厂bean缓存中尝试获取
        if (mbd == null) {

            object = getCachedObjectForFactoryBean(beanName);
        }
        if (object == null) {
            // Return bean instance from factory.
            FactoryBean<?> factory = (FactoryBean<?>) beanInstance;
            // Caches object obtained from FactoryBean if it is a singleton.
//如果mbd为空，并且存在这样的beanDefinition，那么就获取到合并的BeanDefinition
            if (mbd == null && containsBeanDefinition(beanName)) {
                mbd = getMergedLocalBeanDefinition(beanName);
            }
//判断是否为应用程序生成的对象，这里主要为了后面判断是否进行后置处理做判断
            boolean synthetic = (mbd != null && mbd.isSynthetic());
            object = getObjectFromFactoryBean(factory, beanName, !synthetic);
        }
        return object;
    }


FactoryBeanRegistrySupport.getObjectFromFactoryBean

protected Object getObjectFromFactoryBean(FactoryBean<?> factory, String beanName, boolean shouldPostProcess) {
//如果是单例的，并且已经创建好了对应的bean工厂对象
        if (factory.isSingleton() && containsSingleton(beanName)) {
            synchronized (getSingletonMutex()) {
                Object object = this.factoryBeanObjectCache.get(beanName);
                if (object == null) {
//调用工厂bean的getObject方法获取对象
                    object = doGetObjectFromFactoryBean(factory, beanName);
                    // Only post-process and store if not put there already during getObject() call above
                    // (e.g. because of circular reference processing triggered by custom getBean calls)            //再次检查这个bean是否已经被缓存，因为在创建这个bean的时候，有可能因为循环引用调用了getBean，或者用户调用getBean的时候已经前一步创建完成，并且put进这个缓存中
                    Object alreadyThere = this.factoryBeanObjectCache.get(beanName);
                    if (alreadyThere != null) {
                        object = alreadyThere;
                    }
                    else {
                        if (object != null && shouldPostProcess) {
                            try {
//如果不是应用生成的bean，那么就进行初始化后置处理
                                object = postProcessObjectFromFactoryBean(object, beanName);
                            }
                            catch (Throwable ex) {
                                throw new BeanCreationException(beanName,
                                        "Post-processing of FactoryBean‘s singleton object failed", ex);
                            }
                        }
//加入缓存
                        this.factoryBeanObjectCache.put(beanName, (object != null ? object : NULL_OBJECT));
                    }
                }
                return (object != NULL_OBJECT ? object : null);
            }
        }
        else {
//调用bean的工厂方法获取bean
            Object object = doGetObjectFromFactoryBean(factory, beanName);
            if (object != null && shouldPostProcess) {
                try {    
//后置处理
                    object = postProcessObjectFromFactoryBean(object, beanName);
                }
                catch (Throwable ex) {
                    throw new BeanCreationException(beanName, "Post-processing of FactoryBean‘s object failed", ex);
                }
            }
            return object;
        }
    }

DefaultSingletonBeanRegistry.getSingleton

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 the 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 + "‘");
                }
//在创建bean之前记录这个beanName到singletonsCurrentlyInCreation集合中
                beforeSingletonCreation(beanName);
                boolean newSingleton = false;
                boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
                if (recordSuppressedExceptions) {
                    this.suppressedExceptions = new LinkedHashSet<Exception>();
                }
                try {
//调用AbstractAutowireCapableBeanFactory. createBean
                    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;
                    }
//创建成功后从singletonsCurrentlyInCreation移除beanName
                    afterSingletonCreation(beanName);
                }
                if (newSingleton) {
/** this.singletonObjects.put(beanName, (singletonObject != null ? singletonObject : NULL_OBJECT));
* this.singletonFactories.remove(beanName);
* this.earlySingletonObjects.remove(beanName);
* this.registeredSingletons.add(beanName);
*/
                    addSingleton(beanName, singletonObject);
                }
            }
            return (singletonObject != NULL_OBJECT ? singletonObject : null);
        }
    }


AbstractAutowireCapableBeanFactory. createBean

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.
//解析这个BeanDefinition代表的Class类型，因为再配置的时候，class属性可能是一个表达式，需要动态运算出来
        Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
//如果原始的BeanDefinition没有BeanClass，那么就是动态创建的，那么为了不改变原始的BeanDefinition，克隆一个新的BeanDefinition，应为动态计算的class随时都可能会变，比如处理了某些逻辑后，这个BeanDefinition动态计算出来的class发生了改变
        if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
            mbdToUse = new RootBeanDefinition(mbd);
            mbdToUse.setBeanClass(resolvedClass);
        }

        // Prepare method overrides.
        try {
//Look-method replace-method 这里主要是判断对应的方法是否存在（不存在直接抛错）和是否有重载，如果没有就标记没有重载，这样的话，在后面处理这些方法的时候就不需要获取所有的方法，然后进行最优筛选了
            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.
//调用实例化前置处理器，如果前置处理器返回了不为空的bean，那么还会调用实例化后置处理器，最终返回的bean不为空，那么就直接返回。
            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);
        }

        Object beanInstance = doCreateBean(beanName, mbdToUse, args);
        if (logger.isDebugEnabled()) {
            logger.debug("Finished creating instance of bean ‘" + beanName + "‘");
        }
        return beanInstance;
    }


AbstractAutowireCapableBeanFactory.doCreateBean

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) {
//调用bean的构造器去实例bean
            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) {
//应用合并BeanDe的后置处理器
                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.
//如果是单例，并且允许循环一用，并且当前bean正在创建，那么表示允许在未初始化的时候提前曝光
        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");
            }
//添加体检曝光工厂bean
            addSingletonFactory(beanName, new ObjectFactory<Object>() {
                @Override
                public Object getObject() throws BeansException {
                    return getEarlyBeanReference(beanName, mbd, bean);
                }
            });
        }

        // Initialize the bean instance.
        Object exposedObject = bean;
        try {
//注入属性
            populateBean(beanName, mbd, instanceWrapper);
            if (exposedObject != null) {
//初始化bean
                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) {
//如果已经发生过循环依赖，那么可以从早期单例结合中获取到对应的早期bean
            Object earlySingletonReference = getSingleton(beanName, false);
            if (earlySingletonReference != null) {
//如果bean在初始化之后没有被增强处理，那么这里是相等的
                if (exposedObject == bean) {
                    exposedObject = earlySingletonReference;
                }
//如果当前bean被增强过了，并且不允许包装注入并且它有依赖，那么就是发生了循环依赖，并且当前bean和注入到依赖它的bean的那个早期bean已经不是同一版本的bean了，将会抛出错误。
                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 {
//注册销毁
            registerDisposableBeanIfNecessary(beanName, bean, mbd);
        }
        catch (BeanDefinitionValidationException ex) {
            throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
        }

        return exposedObject;
    }