Bean后置處理器 - InstantiationAwareBeanPostProcessor#postProcessProperties

代碼片段:

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

boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
//深度引用檢查, 引用再引用
boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE);

PropertyDescriptor[] filteredPds = null;
if (hasInstAwareBpps) {
    if (pvs == null) {
        pvs = mbd.getPropertyValues();
    }
    for (BeanPostProcessor bp : getBeanPostProcessors()) {
        if (bp instanceof InstantiationAwareBeanPostProcessor) {
            InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
            //這里也是調用的實例化后的后置處理器, 只是調用的方法不一樣
　　　　　　　//這里會進行 @Autowired 和 @Resource 的注入工作
            PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
            if (pvsToUse == null) {
                if (filteredPds == null) {
                    filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
                }
                pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
                if (pvsToUse == null) {
                    return;
                }
            }
            pvs = pvsToUse;
        }
    }
}

同樣的, 通過調試的方式, 來確定這里使用了那些后置處理器:

1.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor

2.CommonAnnotationBeanPostProcessor

3.AutowiredAnnotationBeanPostProcessor

 

ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor

@Override
public PropertyValues postProcessProperties(@Nullable PropertyValues pvs, Object bean, String beanName) {
    // Inject the BeanFactory before AutowiredAnnotationBeanPostProcessor's
    // postProcessProperties method attempts to autowire other configuration beans.
    if (bean instanceof EnhancedConfiguration) {
        ((EnhancedConfiguration) bean).setBeanFactory(this.beanFactory);
    }
    return pvs;
}

這里是對 EnhancedConfiguration 提供支持. 其實他繼承了 BeanFactoryAware 接口, 並且什么都沒干

public interface EnhancedConfiguration extends BeanFactoryAware {}

EnhancedConfiguration 是 ConfigurationClassEnhancer 的一個內部接口, 是給 spring 自己內部使用的, 開發人員用不了這個, 也沒必要

 

CommonAnnotationBeanPostProcessor

@Override
public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) {
    //找出類中標注了@Resource注解的屬性和方法
    //else if (field.isAnnotationPresent(Resource.class))
    InjectionMetadata metadata = findResourceMetadata(beanName, bean.getClass(), pvs);
    try {
        metadata.inject(bean, beanName, pvs);
    }
    catch (Throwable ex) {
        throw new BeanCreationException(beanName, "Injection of resource dependencies failed", ex);
    }
    return pvs;
}

這里主要是對 @Resource 進行注入

findResourceMetadata在MergedBeanDefinitionPostProcessor#postProcessMergedBeanDefinition的時候執行過.

所以這里, 大概率是從緩存中拿取結果, 然后進行注入操作. 事實上, 也確實如此.

 

inject 最終會調用

org.springframework.beans.factory.annotation.InjectionMetadata.InjectedElement#inject 方法

protected void inject(Object target, @Nullable String requestingBeanName, @Nullable PropertyValues pvs)
        throws Throwable {

    if (this.isField) {
        Field field = (Field) this.member;
        ReflectionUtils.makeAccessible(field);
        field.set(target, getResourceToInject(target, requestingBeanName));
    }
    else {
        if (checkPropertySkipping(pvs)) {
            return;
        }
        try {
            Method method = (Method) this.member;
            ReflectionUtils.makeAccessible(method);
            method.invoke(target, getResourceToInject(target, requestingBeanName));
        }
        catch (InvocationTargetException ex) {
            throw ex.getTargetException();
        }
    }
}

這里分兩種情況進行處理, 一種是 通過字段注入, 另一種是通過方法注入.

字段注入的方式是比較多見的. 

getResourceToInject() 方法是一個被重寫了的方法:

org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.ResourceElement#getResourceToInject

他是在一個內部類中被重寫的方法.

@Override
protected Object getResourceToInject(Object target, @Nullable String requestingBeanName) {
    return (this.lazyLookup ? buildLazyResourceProxy(this, requestingBeanName) :
            getResource(this, requestingBeanName));
}

默認情況下, lazy = false, 所以會走 getResource() 方法

org.springframework.context.annotation.CommonAnnotationBeanPostProcessor#getResource

protected Object getResource(LookupElement element, @Nullable String requestingBeanName)
        throws NoSuchBeanDefinitionException {

    if (StringUtils.hasLength(element.mappedName)) {
        return this.jndiFactory.getBean(element.mappedName, element.lookupType);
    }
    if (this.alwaysUseJndiLookup) {
        return this.jndiFactory.getBean(element.name, element.lookupType);
    }
    if (this.resourceFactory == null) {
        throw new NoSuchBeanDefinitionException(element.lookupType,
                "No resource factory configured - specify the 'resourceFactory' property");
    }
    return autowireResource(this.resourceFactory, element, requestingBeanName);
}

根據設置的不同屬性, 進不同的方法, 這里主要看 autowireResource , 因為一般情況是不需要去設置這些屬性的

protected Object autowireResource(BeanFactory factory, LookupElement element, @Nullable String requestingBeanName)
        throws NoSuchBeanDefinitionException {

    Object resource;
    Set<String> autowiredBeanNames;
    String name = element.name;

    if (factory instanceof AutowireCapableBeanFactory) {
        AutowireCapableBeanFactory beanFactory = (AutowireCapableBeanFactory) factory;
        DependencyDescriptor descriptor = element.getDependencyDescriptor();
        //優先使用 根據 name 注入, 這個 name 就是 beanName
        //當 beanName 找不到時, 才就會去根據 type 來注入
        //依據是 !factory.containsBean(name) 
        if (this.fallbackToDefaultTypeMatch && element.isDefaultName && !factory.containsBean(name)) {
            autowiredBeanNames = new LinkedHashSet<>();
            //根據type(類型)來進行依賴注入
            resource = beanFactory.resolveDependency(descriptor, requestingBeanName, autowiredBeanNames, null);
            if (resource == null) {
                //如果返回時 resource , 則表明, spring容器中找不到, 也創建不了 這個依賴的bean
                throw new NoSuchBeanDefinitionException(element.getLookupType(), "No resolvable resource object");
            }
        }
        else {
            //根據name(名稱)來進行依賴注入
            resource = beanFactory.resolveBeanByName(name, descriptor);
            autowiredBeanNames = Collections.singleton(name);
        }
    }
    else {
        resource = factory.getBean(name, element.lookupType);
        autowiredBeanNames = Collections.singleton(name);
    }

    if (factory instanceof ConfigurableBeanFactory) {
        ConfigurableBeanFactory beanFactory = (ConfigurableBeanFactory) factory;
        for (String autowiredBeanName : autowiredBeanNames) {
            if (requestingBeanName != null && beanFactory.containsBean(autowiredBeanName)) {
                beanFactory.registerDependentBean(autowiredBeanName, requestingBeanName);
            }
        }
    }

    return resource;
}

都說, @Resource 在不設置 name 和 type 的情況下, 是優先使用 name 去 獲取/創建 依賴的 bean , 如果name找不到, 才會使用 type.

這段代碼, 就是支撐的依據.

 

AutowiredAnnotationBeanPostProcessor

@Override
public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) {
    InjectionMetadata metadata = findAutowiringMetadata(beanName, bean.getClass(), pvs);
    try {
        metadata.inject(bean, beanName, pvs);
    }
    catch (BeanCreationException ex) {
        throw ex;
    }
    catch (Throwable ex) {
        throw new BeanCreationException(beanName, "Injection of autowired dependencies failed", ex);
    }
    return pvs;
}

這里主要是對 @Autowired 和 @Value 進行注入的. findAutowiringMetadata

findAutowiringMetadata在MergedBeanDefinitionPostProcessor#postProcessMergedBeanDefinition的時候執行過.

所以此處, 是從緩存中拿取結果, 然后進行注入操作.

最終會調用本類中的方法:

org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.AutowiredFieldElement#inject

@Override
protected void inject(Object bean, @Nullable String beanName, @Nullable PropertyValues pvs) throws Throwable {
    Field field = (Field) this.member;
    Object value;
    if (this.cached) {
        value = resolvedCachedArgument(beanName, this.cachedFieldValue);
    }
    else {
        DependencyDescriptor desc = new DependencyDescriptor(field, this.required);
        desc.setContainingClass(bean.getClass());
        Set<String> autowiredBeanNames = new LinkedHashSet<>(1);
        Assert.state(beanFactory != null, "No BeanFactory available");
        TypeConverter typeConverter = beanFactory.getTypeConverter();
        try {
            //先根據 type 進行匹配, 當有多個type時, 在根據name進行匹配, 如果匹配不上則拋出異常
            value = beanFactory.resolveDependency(desc, beanName, autowiredBeanNames, typeConverter);
        }
        catch (BeansException ex) {
            throw new UnsatisfiedDependencyException(null, beanName, new InjectionPoint(field), ex);
        }
        synchronized (this) {
            if (!this.cached) {
                if (value != null || this.required) {
                    this.cachedFieldValue = desc;
                    registerDependentBeans(beanName, autowiredBeanNames);
                    if (autowiredBeanNames.size() == 1) {
                        String autowiredBeanName = autowiredBeanNames.iterator().next();
                        if (beanFactory.containsBean(autowiredBeanName) &&
                                beanFactory.isTypeMatch(autowiredBeanName, field.getType())) {
                            this.cachedFieldValue = new ShortcutDependencyDescriptor(
                                    desc, autowiredBeanName, field.getType());
                        }
                    }
                }
                else {
                    this.cachedFieldValue = null;
                }
                this.cached = true;
            }
        }
    }
    if (value != null) {
        ReflectionUtils.makeAccessible(field);
        field.set(bean, value);
    }
}

 

這里有一個隱藏的后置處理器: SmartInstantiationAwareBeanPostProcessor

留到下一篇看