spring技术杂谈

Spring IOC 源码解析五（非延迟加载bean的初始化）

2018-11-29  本文已影响45人  香芋牛奶面包

引言

上期分析了refresh方法中大部分，这期我们只分析finishBeanFactoryInitialization(beanFactory)这一个方法，分析这个方法的过程中我们会顺藤摸瓜把bean初始化的整个流程都分析一遍

finishBeanFactoryInitialization(beanFactory)

提前初始化一些非延迟加载的单例类型的bean，这里主要看最后一行 beanFactory.preInstantiateSingletons(),这里是初始化非延迟加载单例的入口

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
    // 初始化类型转化的bean
    if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
            beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
        beanFactory.setConversionService(
                beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
    }

    // Register a default embedded value resolver if no bean post-processor
    // (such as a PropertyPlaceholderConfigurer bean) registered any before:
    // at this point, primarily for resolution in annotation attribute values.
    // 注册默认的值解析器
    if (!beanFactory.hasEmbeddedValueResolver()) {
        beanFactory.addEmbeddedValueResolver(new StringValueResolver() {
            @Override
            public String resolveStringValue(String strVal) {
                return getEnvironment().resolvePlaceholders(strVal);
            }
        });
    }

    // Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
    String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
    for (String weaverAwareName : weaverAwareNames) {
        getBean(weaverAwareName);
    }

    // Stop using the temporary ClassLoader for type matching.
    beanFactory.setTempClassLoader(null);

    // Allow for caching all bean definition metadata, not expecting further changes.
    beanFactory.freezeConfiguration();

    // Instantiate all remaining (non-lazy-init) singletons.
    beanFactory.preInstantiateSingletons();
}

preInstantiateSingletons

方法在DefaultListableBeanFactory中，用于初始化所有非延迟加载的单例

public void preInstantiateSingletons() throws BeansException {
    if (this.logger.isDebugEnabled()) {
        this.logger.debug("Pre-instantiating singletons in " + this);
    }

    // 所有注册完成的 beanDefinitionNames 
    List<String> beanNames = new ArrayList<String>(this.beanDefinitionNames);

    // 遍历所有非延迟加载的单例类型
    for (String beanName : beanNames) {
        RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
        if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
            // 判断类型是否为 FactoryBean
            if (isFactoryBean(beanName)) {
                final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
                boolean isEagerInit;
                if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                    isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
                        @Override
                        public Boolean run() {
                            return ((SmartFactoryBean<?>) factory).isEagerInit();
                        }
                    }, getAccessControlContext());
                }
                else {
                    isEagerInit = (factory instanceof SmartFactoryBean &&
                            ((SmartFactoryBean<?>) factory).isEagerInit());
                }
                // 是否需要立即加载
                if (isEagerInit) {
                    getBean(beanName);
                }
            }
            else {
                getBean(beanName);
            }
        }
    }

    // Trigger post-initialization callback for all applicable beans...
    for (String beanName : beanNames) {
        Object singletonInstance = getSingleton(beanName);
        if (singletonInstance instanceof SmartInitializingSingleton) {
            final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
            if (System.getSecurityManager() != null) {
                AccessController.doPrivileged(new PrivilegedAction<Object>() {
                    @Override
                    public Object run() {
                        smartSingleton.afterSingletonsInstantiated();
                        return null;
                    }
                }, getAccessControlContext());
            }
            else {
                smartSingleton.afterSingletonsInstantiated();
            }
        }
    }
}

可以看到这段代码主要做了2个事情

  1. 判断bean的类型是否是factoryBean，如果是的话判断类型是不是SmartFactoryBean，再获取是否需要立即加载的isEagerInit属性，执行getBean方法
  2. 在单例bean都初始化完成后，循环判断bean的类型是否是SmartInitializingSingleton，是的话会在这时候执行afterSingletonsInstantiated方法

接下来就是获取bean的流程代码

getBean

getBean方法最终都是走的doGetBean方法

public Object getBean(String name) throws BeansException {
    return doGetBean(name, null, null, false);
}

doGetBean

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;

    // 首先检查缓存是否有，有则直接取
    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 + "'");
            }
        }
        // 这里是取FactoryBean 
        bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
    }
    
    // 缓存里没有 第一次初始化Bean
    else {
        // 判断是不是处于循环依赖当中，有则直接报错
        if (isPrototypeCurrentlyInCreation(beanName)) {
            throw new BeanCurrentlyInCreationException(beanName);
        }

        // 检查父容器是否存在此Bean的定义
        BeanFactory parentBeanFactory = getParentBeanFactory();
        if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
            // Not found -> check parent.
            // 返回原始的名称 加上FactoryBean符号
            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) {
            // 把Bean的状态改为已创建，并从mergedBeanDefinitions 中移除
            markBeanAsCreated(beanName);
        }

        try {
            // 合并BeanDefinition转化成RootBeanDefinition
            final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
            checkMergedBeanDefinition(mbd, beanName, args);

            // 获取配置的 depends-On 依赖,优先加载
            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);
                    try {
                        // 递归获取
                        getBean(dep);
                    }
                    catch (NoSuchBeanDefinitionException ex) {
                        throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                                "'" + beanName + "' depends on missing bean '" + dep + "'", ex);
                    }
                }
            }

            // Create bean instance.
            // 如果是单例
            if (mbd.isSingleton()) {
                // 这里会把创建完成的bean加入缓存
                sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
                    @Override
                    public Object getObject() throws BeansException {
                        try {
                            // 创建bean的主逻辑
                            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);
            }
            
            // 判断类型 prototype 有状态的bean
            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 {
                // 其他类型的scope
                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.
    // 如果有指定的类型，则检查是否与实际bean实例的类型匹配
    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;
}

看完上面的代码，我们作总结：
首先，创建bean之前会检查单例缓存里有没有，有的话会直接返回。然后会检查父容器是否有这个bean的定义，一直找到最顶层的父容器（有点类型双亲委派），最后会在父容器执行这个bean的获取，之后获取depends-On如果有配置的话会优先获取（递归获取直到依赖的所有depends-On），最后才是根据scope调用AbstractAutowireCapableBeanFactory的createBean方法

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.
    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.
        // 扩展点，可以通过实现InstantiationAwareBeanPostProcessor 接口一个返回代理而不是目标bean实例
        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;
}

这段代码主要看一下resolveBeforeInstantiation(beanName, mbdToUse)，这里是spring提供的一个扩展点，可以通过实现InstantiationAwareBeanPostProcessor接口在这里返回bean的代理
然后就可以直接看最后的doCreateBean(beanName, mbdToUse, args)方法

doCreateBean

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

    // Instantiate the bean.
    // 封装bean的容器
    BeanWrapper instanceWrapper = null;
    if (mbd.isSingleton()) {
        instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
    }
    if (instanceWrapper == null) {
        // 这里是创建 BeanWrapper 
        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;
        }
    }

    // 判断是否需要提前暴露对象的引用，用于解决循环依赖
    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 {
        // 依赖注入的主逻辑
        populateBean(beanName, mbd, instanceWrapper);
        if (exposedObject != null) {
            //  执行一些初始化的方法
            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;
}

这段代码主要看这三个方法

  1. createBeanInstance(beanName, mbd, args) 创建bean
  2. populateBean(beanName, mbd, instanceWrapper) 组装bean的依赖
  3. initializeBean(beanName, exposedObject, mbd) 调用bean的一些初始化方法，以及扩展接口

接下来我们着重来看这三个方法

createBeanInstance

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, Object[] args) {
    // Make sure bean class is actually resolved at this point.
    // 获取bean class
    Class<?> beanClass = resolveBeanClass(mbd, beanName);

    // 不是 pullic 直接抛异常
    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());
    }
    // 使用工厂方法实例化bean
    if (mbd.getFactoryMethodName() != null)  {
        return instantiateUsingFactoryMethod(beanName, mbd, args);
    }

    // Shortcut when re-creating the same bean...
    // 判断bean是否创建过
    boolean resolved = false;
    boolean autowireNecessary = false;
    if (args == null) {
        synchronized (mbd.constructorArgumentLock) {
            if (mbd.resolvedConstructorOrFactoryMethod != null) {
                resolved = true;
                autowireNecessary = mbd.constructorArgumentsResolved;
            }
        }
    }
    // 如果已经加载过
    if (resolved) {
        if (autowireNecessary) {
            // 有参构造方法
            return autowireConstructor(beanName, mbd, null, null);
        }
        else {
            // 使用无参构造
            return instantiateBean(beanName, mbd);
        }
    }

    // Need to determine the constructor...
    // 寻找一个合适的构造方法
    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);
}

这个方法的主要逻辑其实就是在找一个合适的初始化方法

  1. 首先判断RootBeanDefinition是否含有factory-method配置，有的话使用工厂方法实例化bean
  2. 之后的逻辑就是寻找一个合适的构造方法用于bean的实例化
    • 如果判断是有参的构造方法，则通过autowireConstructor实例化，初始化的过程很繁琐，其中对构造方法参数的依赖也是通过递归getBean()来实现的
    • 无参的则使用instantiateBean实例化

到这里执行完bean已经创建了(spring默认是使用CGLIB)，但是这时候的bean是不完整的，相关的依赖项还并没有被注入

populateBean(beanName, mbd, instanceWrapper)

组装bean的逻辑都在这里

protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
    // 获取的配置的property依赖
    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;
        }
    }

    // 扩展点 执行实现了InstantiationAwareBeanPostProcessors接口方法
    // 在设置属性依赖之前可以有机会修改bean的属性配置
    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;
                }
            }
        }
    }
    
    // 判断是否需要继续组装bean属性
    if (!continueWithPropertyPopulation) {
        return;
    }
    
    // 判断自动配的类型（按名称和按类型）
    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.
        // 按bean的名称注入
        if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
            autowireByName(beanName, mbd, bw, newPvs);
        }

        // Add property values based on autowire by type if applicable.
        // 按bean的类型注入
        if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
            autowireByType(beanName, mbd, bw, newPvs);
        }

        pvs = newPvs;
    }

    // 判断是否需要依赖检查
    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) {
            // 检查依赖
            checkDependencies(beanName, mbd, filteredPds, pvs);
        }
    }
    
    // 组装属性
    applyPropertyValues(beanName, mbd, bw, pvs);
}

通过查看代码，可知上面不止做了组装bean这一件事，主要做了下面几件事情:

  1. 获取spring配置项中配置的property属性依赖
  2. 执行实现了InstantiationAwareBeanPostProcessors接口的方法，该接口可以在属性被注入前做一些修改，并且可以直接返回，不执行下面的属性注入逻辑
  3. 判断是否有配置自动注入，有的话会按配置执行按名称（autowireByName方法）或类型（autowireByType方法）注入
  4. 判断是否执行依赖检查（按配置的依赖检查等级check）
  5. 最后执行bean属性的最终装配 （applyPropertyValues(beanName, mbd, bw, pvs)）

我们可以简单看一下 autowireByName的实现

autowireByName

protected void autowireByName(
        String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {
    
    // 返回需要自动依赖注入的属性名称
    String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
    for (String propertyName : propertyNames) {
        if (containsBean(propertyName)) {
            Object bean = getBean(propertyName);
            // 将获取的依赖bean放回 待装配
            pvs.add(propertyName, bean);
            registerDependentBean(propertyName, beanName);
            if (logger.isDebugEnabled()) {
                logger.debug("Added autowiring by name from bean name '" + beanName +
                        "' via property '" + propertyName + "' to bean named '" + propertyName + "'");
            }
        }
        else {
            if (logger.isTraceEnabled()) {
                logger.trace("Not autowiring property '" + propertyName + "' of bean '" + beanName +
                        "' by name: no matching bean found");
            }
        }
    }
}

可知如果是按name注入的话，首先会先获取需要自动依赖注入的bean名称，然后是通过getBean(beanName)获取依赖项的。同理autowireByType

applyPropertyValues

在执行applyPropertyValues方法之前，我们已经准备好了所有的依赖项了，接下来的事情就是把这些依赖项装配到bean对应的属性中

protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
    // 待装配的属性为空 直接返回
    if (pvs == null || pvs.isEmpty()) {
        return;
    }

    MutablePropertyValues mpvs = null;
    List<PropertyValue> original;

    if (System.getSecurityManager() != null) {
        if (bw instanceof BeanWrapperImpl) {
            ((BeanWrapperImpl) bw).setSecurityContext(getAccessControlContext());
        }
    }
    // 
    if (pvs instanceof MutablePropertyValues) {
        mpvs = (MutablePropertyValues) pvs;
        if (mpvs.isConverted()) {
            // Shortcut: use the pre-converted values as-is.
            try {
                bw.setPropertyValues(mpvs);
                return;
            }
            catch (BeansException ex) {
                throw new BeanCreationException(
                        mbd.getResourceDescription(), beanName, "Error setting property values", ex);
            }
        }
        original = mpvs.getPropertyValueList();
    }
    else {
        original = Arrays.asList(pvs.getPropertyValues());
    }

    TypeConverter converter = getCustomTypeConverter();
    if (converter == null) {
        converter = bw;
    }
    // 用于加载beanDefinition所对应的值
    BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);

    // 创建一个PropertyValue的深拷贝
    List<PropertyValue> deepCopy = new ArrayList<PropertyValue>(original.size());
    boolean resolveNecessary = false;
    for (PropertyValue pv : original) {
        if (pv.isConverted()) {
            deepCopy.add(pv);
        }
        else {
            String propertyName = pv.getName();
            Object originalValue = pv.getValue();
            // 加载对应属性值 value
            Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
            Object convertedValue = resolvedValue;
            boolean convertible = bw.isWritableProperty(propertyName) &&
                    !PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
            if (convertible) {
                convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);
            }
            // Possibly store converted value in merged bean definition,
            // in order to avoid re-conversion for every created bean instance.
            if (resolvedValue == originalValue) {
                if (convertible) {
                    pv.setConvertedValue(convertedValue);
                }
                deepCopy.add(pv);
            }
            else if (convertible && originalValue instanceof TypedStringValue &&
                    !((TypedStringValue) originalValue).isDynamic() &&
                    !(convertedValue instanceof Collection || ObjectUtils.isArray(convertedValue))) {
                pv.setConvertedValue(convertedValue);
                deepCopy.add(pv);
            }
            else {
                resolveNecessary = true;
                deepCopy.add(new PropertyValue(pv, convertedValue));
            }
        }
    }
    if (mpvs != null && !resolveNecessary) {
        mpvs.setConverted();
    }

    // Set our (possibly massaged) deep copy.
    try {
        // 设置属性信息
        bw.setPropertyValues(new MutablePropertyValues(deepCopy));
    }
    catch (BeansException ex) {
        throw new BeanCreationException(
                mbd.getResourceDescription(), beanName, "Error setting property values", ex);
    }
}

这段代码做的主要事情就是通过配置的属性去加载属性对应的值，真正为bean设置属性的逻辑在bw.setPropertyValues(new MutablePropertyValues(deepCopy))中，这里其实就是通过反射调用set方法进行属性的设置的。
代码执行到这里，bean的创建已经基本完整了,populateBean方法的工作已经完成了，下面要做的就是一些初始化的工作

initializeBean(beanName, exposedObject, mbd)

protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
    // 安全管理器 判断执行权限
    if (System.getSecurityManager() != null) {
        AccessController.doPrivileged(new PrivilegedAction<Object>() {
            @Override
            public Object run() {
                invokeAwareMethods(beanName, bean);
                return null;
            }
        }, getAccessControlContext());
    }
    else {
        // 执行实现了一系列Aware的接口方法
        invokeAwareMethods(beanName, bean);
    }

    Object wrappedBean = bean;
    if (mbd == null || !mbd.isSynthetic()) {
        // 执行BeanPostProcessor接口postProcessBeforeInitialization方法
        wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
    }

    try {
        // 先执行InitializingBean接口afterPropertiesSet方法
        // 再执行自定义配置的初始化方法(init-method)
        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()) {
        // 执行BeanPostProcessor接口postProcessAfterInitialization方法
        wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
    }
    return wrappedBean;
}

上述代码做的都是bean初始化的事情

  1. invokeAwareMethods方法，如果有bean又实现Aware相关的接口，则调用这些接口的方法给bean注入一些信息(beanName，BeanClassLoader，BeanFactory)
  2. applyBeanPostProcessorsBeforeInitialization 执行BeanPostProcessor接口postProcessBeforeInitialization方法，BeanPostProcessor接口在上一篇解析中有讲到过，是在refresh方法的registerBeanPostProcessors(beanFactory)中注册的，是spring提供的非常重要的一个自定义扩展点
  3. invokeInitMethods方法，这里是判断是否有实现InitializingBean接口，有则执行afterPropertiesSet初始化方法，并且如果有配置自定义的init-method方法则也一并执行
  4. applyBeanPostProcessorsBeforeInitialization 执行BeanPostProcessor接口postProcessAfterInitialization方法

尾言

随着解析进行到这里，我们已经把bean的整个生命周期都走了个大概。相信大家对spring ioc 的具体实现已经有了个基本的了解了

博客原文地址戳这里

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