Spring bean的生命周期

学习spring源码主框架，从源码角度开发学习Spring bean的生命周期。

spring创建bean方法

org.springframework.beans.factory.support.AbstractBeanFactory#getBean(java.lang.String, java.lang.Class )

public <T> T getBean(String name, Class<T> requiredType) throws BeansException {
        //doGetBean是获取bean的真实方法
        return doGetBean(name, requiredType, null, false);
    }

真正执行spring创建bean方法doGetBean

org.springframework.beans.factory.support.AbstractBeanFactory#doGetBean

protected <T> T doGetBean(
            final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
            throws BeansException {
        //获取的beanname可能是重命名后的，这个获取原始的beanname，这里做别名解析
        final String beanName = transformedBeanName(name);
        Object bean;

        //先从spring缓存池中获取bean，这里是解决循环依赖的根本
        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 + "'");
                }
            }
            //如果从缓存中获取到bean，进行后续处理。
            bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
        }

        else {
            //判断当前创建的bean是不是原型的，如果存在循环依赖，则抛异常
            if (isPrototypeCurrentlyInCreation(beanName)) {
                throw new BeanCurrentlyInCreationException(beanName);
            }

            //获取父工厂
            BeanFactory parentBeanFactory = getParentBeanFactory();
            //判断父工厂是否为空，以及当前容器中是否包含bean定义
            if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
                // Not found -> check parent.
                String nameToLookup = originalBeanName(name);
                //根据构造函数是否有参数，来创建不同的bean
                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);
            }

            try {
                //合并bean定义，存在抽象父bean定义，专门给子bean做继承的
                final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
                //检查bean定义的是否为抽象的，如果是则抛出异常
                checkMergedBeanDefinition(mbd, beanName, args);

                //获取bean初始化的前置依赖beanname
                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 + "'");
                        }
                        //解析以来的bean，并注册依赖的bean
                        registerDependentBean(dep, beanName);
                        try {
                            //递归调用获取依赖bean
                            getBean(dep);
                        }
                        catch (NoSuchBeanDefinitionException ex) {
                            throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                                    "'" + beanName + "' depends on missing bean '" + dep + "'", ex);
                        }
                    }
                }

                // 创建bean的实例
                if (mbd.isSingleton()) {
                    sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
                        @Override
                        public Object getObject() throws BeansException {
                            try {
                                //构建bean的实例
                                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;
                            }
                        }
                    });
                    //如果获取的bean是factroybean，那么要处理工厂bean。
                    bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
                }

                else if (mbd.isPrototype()) {
                    //创建原型bean
                    Object prototypeInstance = null;
                    try {
                        //在原型bena创建之前回调底层spring函数，开放性方法
                        beforePrototypeCreation(beanName);
                        prototypeInstance = createBean(beanName, mbd, args);
                    }
                    finally {
                        //开放性方法
                        afterPrototypeCreation(beanName);
                    }
                    //如果获取的bean是factroybean，那么要处理工厂bean。
                    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 {
                        //根据bean定义的scope来创建bean
                        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;
            }
        }

        // 判断获取的类型是否匹配实际的bean实例
        if (requiredType != null && bean != null && !requiredType.isInstance(bean)) {
            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;
    }

org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#getSingleton(java.lang.String, boolean)

这个方法是解决spring循环依赖问题

protected Object getSingleton(String beanName, boolean allowEarlyReference) {
        //从一级缓存中获取实例bean，如果有直接返回对象
        Object singletonObject = this.singletonObjects.get(beanName);
        //singletonObject为空并且 beanname是否正在创建中的标识
        if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
            //防止并发获取bean
            synchronized (this.singletonObjects) {
                //从earlySingletonObjects早期缓冲池中获取bean
                singletonObject = this.earlySingletonObjects.get(beanName);
                if (singletonObject == null && allowEarlyReference) {
                    //从singletonFactories中获取bean的objectfactory
                    ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
                    if (singletonFactory != null) {
                        //调用objectfactory的getObject方法获取singletonObject
                        singletonObject = singletonFactory.getObject();
                        //同时放到earlySingletonObjects提前暴露出来
                        this.earlySingletonObjects.put(beanName, singletonObject);
                        //并从singletonFactories移除
                        this.singletonFactories.remove(beanName);
                    }
                }
            }
        }
        return (singletonObject != NULL_OBJECT ? singletonObject : null);
    }

获取实例bean

org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#getSingleton(java.lang.String, org.springframework.beans.factory.ObjectFactory<?>)

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 + "'");
                }
                //标识当前正在创建的对象，放到singletonsCurrentlyInCreation缓存中
                beforeSingletonCreation(beanName);
                boolean newSingleton = false;
                boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
                if (recordSuppressedExceptions) {
                    this.suppressedExceptions = new LinkedHashSet<Exception>();
                }
                try {
                    //调用接口objectfacotry的getObject方法， 这个方法被重写
                    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;
                    }
                    //当前bean已经创建好了，到singletonsCurrentlyInCreation中bean移除掉
                    afterSingletonCreation(beanName);
                }
                if (newSingleton) {
                    //把创建好的bean加载到缓存池中，并移除二三级缓存
                    addSingleton(beanName, singletonObject);
                }
            }
            //对bean判空
            return (singletonObject != NULL_OBJECT ? singletonObject : null);
        }
    }

创建bean实例

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#createBean(java.lang.String, org.springframework.beans.factory.support.RootBeanDefinition, java.lang.Object[])

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 {
            // 这里给后置处理器一个机会去创建代理对象，第一次创建bean到这里还没有创建好bean， 仅仅把切面信息解析出来放入缓存中
            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);
        }

        //真正执行创建bean实例的方法doCreateBean
        Object beanInstance = doCreateBean(beanName, mbdToUse, args);
        if (logger.isDebugEnabled()) {
            logger.debug("Finished creating instance of bean '" + beanName + "'");
        }
        return beanInstance;
    }

真正执行创建Bean

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#doCreateBean

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
            throws BeanCreationException {

        // Instantiate the bean.
        BeanWrapper instanceWrapper = null;
        if (mbd.isSingleton()) {
            instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
        }
        if (instanceWrapper == null) {
            //根据@bean， @autowire来创建有参构造函数， 或者无参数构造函数
            instanceWrapper = createBeanInstance(beanName, mbd, args);
        }
        final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
        Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
        mbd.resolvedTargetType = beanType;
        
        //允许后置处理器去修改merge后的bean定义
        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;
            }
        }

        // 判断earlySingletonObjects是否提前暴露bean对象
        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");
            }
            //将已经创建好但是属性还没有赋值的bean对象，通过objectfacotry的形式来加载到缓存中用来解决循环依赖的问题
            addSingletonFactory(beanName, new ObjectFactory<Object>() {
                @Override
                public Object getObject() throws BeansException {
                    return getEarlyBeanReference(beanName, mbd, bean);
                }
            });
        }

        // Initialize the bean instance.
        Object exposedObject = bean;
        try {
            //为刚刚创建的bean对象进行赋值
            populateBean(beanName, mbd, instanceWrapper);
            if (exposedObject != null) {
                //初始化bean，并且通过开放性方法为bean赋值
                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.");
                    }
                }
            }
        }

        try {
            //注册自定义销毁bean的方法
            registerDisposableBeanIfNecessary(beanName, bean, mbd);
        }
        catch (BeanDefinitionValidationException ex) {
            throw new BeanCreationException(
                    mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
        }

        return exposedObject;
    }

初始化已经创建好的bean实例

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#initializeBean(java.lang.String, java.lang.Object, org.springframework.beans.factory.support.RootBeanDefinition)

protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
        //权限校验是否判断是否可以回调底层组件方法
        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()) {
          //实现自定义的bean的后置处理器的前置方法
            wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
        }

        try {
            //调用自定义的init方法或InitializingBean
            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()) {
            //实现自定义的bean的后置处理器的后置方法
            wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
        }
        return wrappedBean;
    }

以上，就是spring ioc模块bean生命周期的源代码解析。

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