城市建设杂志社网站,局域网网站怎么做,wordpress黑色主题,淘宝客如何做自己的网站解决SpringBean循环依赖为什么需要3级缓存#xff1f;回答#xff1a;1级Map保存单例bean。2级Map 为了保证产生循环引用问题时#xff0c;每次查询早期引用对象#xff0c;都拿到同一个对象。3级Map保存ObjectFactory对象。数据结构1级Map singletonObjects2级Map earlySi…解决SpringBean循环依赖为什么需要3级缓存回答1级Map保存单例bean。2级Map 为了保证产生循环引用问题时每次查询早期引用对象都拿到同一个对象。3级Map保存ObjectFactory对象。数据结构1级Map singletonObjects2级Map earlySingletonObjects3级Map singletonFactoriesboolean allowCircularReference 是否允许循环引用源码DefaultSingletonBeanRegistry /** Cache of singleton objects: bean name to bean instance. */private final MapString, Object singletonObjects new ConcurrentHashMap(256);/** Cache of singleton factories: bean name to ObjectFactory. */private final MapString, ObjectFactory? singletonFactories new HashMap(16);/** Cache of early singleton objects: bean name to bean instance. */private final MapString, Object earlySingletonObjects new ConcurrentHashMap(16);依赖注入理解走InstantiationAwareBeanPostProcessor.postProcessProperties最终还是调用DefaultListableBeanFactory.getBean获取bean实例进行依赖注入。重点是从Map缓存读取实例逻辑DefaultSingletonBeanRegistry#getSingleton /*** Return the (raw) singleton object registered under the given name.* pChecks already instantiated singletons and also allows for an early* reference to a currently created singleton (resolving a circular reference).* param beanName the name of the bean to look for* param allowEarlyReference whether early references should be created or not* return the registered singleton object, or {code null} if none found*/Nullableprotected Object getSingleton(String beanName, boolean allowEarlyReference) {// Quick check for existing instance without full singleton lockObject singletonObject this.singletonObjects.get(beanName);if (singletonObject null isSingletonCurrentlyInCreation(beanName)) {singletonObject this.earlySingletonObjects.get(beanName);if (singletonObject null allowEarlyReference) {synchronized (this.singletonObjects) {// Consistent creation of early reference within full singleton locksingletonObject this.singletonObjects.get(beanName);if (singletonObject null) {singletonObject this.earlySingletonObjects.get(beanName);if (singletonObject null) {ObjectFactory? singletonFactory this.singletonFactories.get(beanName);if (singletonFactory ! null) {singletonObject singletonFactory.getObject();this.earlySingletonObjects.put(beanName, singletonObject);this.singletonFactories.remove(beanName);}}}}}}return singletonObject;}AbstractAutowiredCapableBeanFactory#doCreateBeanprotected Object doCreateBean(String beanName, RootBeanDefinition mbd, Nullable Object[] args)// 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.isTraceEnabled()) {logger.trace(Eagerly caching bean beanName to allow for resolving potential circular references);}addSingletonFactory(beanName, () - getEarlyBeanReference(beanName, mbd, bean));}}AbstractAutowiredCapableBeanFactory#getEarlyReference protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {Object exposedObject bean;if (!mbd.isSynthetic() hasInstantiationAwareBeanPostProcessors()) {for (SmartInstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().smartInstantiationAware) {exposedObject bp.getEarlyBeanReference(exposedObject, beanName);}}return exposedObject;}DefaultSingletonBeanRegistry#addSingletonFactory /*** Add the given singleton factory for building the specified singleton* if necessary.* pTo be called for eager registration of singletons, e.g. to be able to* resolve circular references.* param beanName the name of the bean* param singletonFactory the factory for the singleton object*/protected void addSingletonFactory(String beanName, ObjectFactory? singletonFactory) {Assert.notNull(singletonFactory, Singleton factory must not be null);synchronized (this.singletonObjects) {if (!this.singletonObjects.containsKey(beanName)) {this.singletonFactories.put(beanName, singletonFactory);this.earlySingletonObjects.remove(beanName);this.registeredSingletons.add(beanName);}}}依赖注入的入口调用实例化扩展点处理 InstantiationAwareBeanPostProcessor.postProcessProperties源码AbstractAutowiredCapableBeanFactory#populateBean--接口 InstantiationAwareBeanPostProcessor.postProcessProperties---- 实现类AutowireAnnotationBeanPostProcssor.postProcessProperties----- metadata.inject------ 实现类AutowriedFieldElement.inject ------- AutowriedFieldElement.resolveFiledValue-------- beanFactory.resolveDependencyInstantiationAwareBeanPostProcessor.postProcessProperties Overridepublic PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) {
//获取bean的依赖注入的元数据InjectionMetadata metadata findAutowiringMetadata(beanName, bean.getClass(), pvs);//依赖注入metadata.inject(bean, beanName, pvs);return pvs;}取依赖注入元数据调其inject注入 public void inject(Object target, Nullable String beanName, Nullable PropertyValues pvs) throws Throwable {CollectionInjectedElement checkedElements this.checkedElements;CollectionInjectedElement elementsToIterate (checkedElements ! null ? checkedElements : this.injectedElements);if (!elementsToIterate.isEmpty()) {for (InjectedElement element : elementsToIterate) {element.inject(target, beanName, pvs);}}}AutowiredFieldElement#inject Overrideprotected void inject(Object bean, Nullable String beanName, Nullable PropertyValues pvs) throws Throwable {Field field (Field) this.member;value resolveFieldValue(field, bean, beanName);ReflectionUtils.makeAccessible(field);field.set(bean, value);}AutowiredFiledElement#resolveFieldValue Nullableprivate Object resolveFieldValue(Field field, Object bean, Nullable String beanName) {DependencyDescriptor desc new DependencyDescriptor(field, this.required);desc.setContainingClass(bean.getClass());SetString autowiredBeanNames new LinkedHashSet(1);TypeConverter typeConverter beanFactory.getTypeConverter();Object value;value beanFactory.resolveDependency(desc, beanName, autowiredBeanNames, typeConverter); return value;}DefaultListableBeanFactory#resolveDependency OverrideNullablepublic Object resolveDependency(DependencyDescriptor descriptor, Nullable String requestingBeanName,Nullable SetString autowiredBeanNames, Nullable TypeConverter typeConverter) throws BeansException {descriptor.initParameterNameDiscovery(getParameterNameDiscoverer());Object result getAutowireCandidateResolver().getLazyResolutionProxyIfNecessary(descriptor, requestingBeanName);if (result null) {result doResolveDependency(descriptor, requestingBeanName, autowiredBeanNames, typeConverter);}return result;}DefaultListableBeanFactory#doResolveDependencyNullablepublic Object doResolveDependency(DependencyDescriptor descriptor, Nullable String beanName,Nullable SetString autowiredBeanNames, Nullable TypeConverter typeConverter) throws BeansException {InjectionPoint previousInjectionPoint ConstructorResolver.setCurrentInjectionPoint(descriptor);try {Object shortcut descriptor.resolveShortcut(this);if (shortcut ! null) {return shortcut;}Class? type descriptor.getDependencyType();Object value getAutowireCandidateResolver().getSuggestedValue(descriptor);if (value ! null) {if (value instanceof String) {String strVal resolveEmbeddedValue((String) value);BeanDefinition bd (beanName ! null containsBean(beanName) ?getMergedBeanDefinition(beanName) : null);value evaluateBeanDefinitionString(strVal, bd);}TypeConverter converter (typeConverter ! null ? typeConverter : getTypeConverter());try {return converter.convertIfNecessary(value, type, descriptor.getTypeDescriptor());}catch (UnsupportedOperationException ex) {// A custom TypeConverter which does not support TypeDescriptor resolution...return (descriptor.getField() ! null ?converter.convertIfNecessary(value, type, descriptor.getField()) :converter.convertIfNecessary(value, type, descriptor.getMethodParameter()));}} //处理多类型的bean 比如Steam 、 array、Collection、MapObject multipleBeans resolveMultipleBeans(descriptor, beanName, autowiredBeanNames, typeConverter);if (multipleBeans ! null) {return multipleBeans;}//查询依赖注入候选bean MapString, Object matchingBeans findAutowireCandidates(beanName, type, descriptor);//若匹配的bean为空则抛出不能找到匹配的bean异常if (matchingBeans.isEmpty()) {if (isRequired(descriptor)) {raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);}return null;}String autowiredBeanName;Object instanceCandidate;// 若匹配多个候选bean按规则标记Primary的bean 、取PriorityOrder排序取、按字段名注入取若都未取到抛出获取bean不唯一异常if (matchingBeans.size() 1) {autowiredBeanName determineAutowireCandidate(matchingBeans, descriptor);if (autowiredBeanName null) {if (isRequired(descriptor) || !indicatesMultipleBeans(type)) {return descriptor.resolveNotUnique(descriptor.getResolvableType(), matchingBeans);}else {// In case of an optional Collection/Map, silently ignore a non-unique case:// possibly it was meant to be an empty collection of multiple regular beans// (before 4.3 in particular when we didnt even look for collection beans).return null;}}instanceCandidate matchingBeans.get(autowiredBeanName);}else {// We have exactly one match.Map.EntryString, Object entry matchingBeans.entrySet().iterator().next();autowiredBeanName entry.getKey();instanceCandidate entry.getValue();}if (autowiredBeanNames ! null) {autowiredBeanNames.add(autowiredBeanName);}if (instanceCandidate instanceof Class) {instanceCandidate descriptor.resolveCandidate(autowiredBeanName, type, this);}Object result instanceCandidate;if (result instanceof NullBean) {if (isRequired(descriptor)) {raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);}result null;}if (!ClassUtils.isAssignableValue(type, result)) {throw new BeanNotOfRequiredTypeException(autowiredBeanName, type, instanceCandidate.getClass());}return result;}finally {ConstructorResolver.setCurrentInjectionPoint(previousInjectionPoint);}}
DefaultListableBeanFactory#findAutowireCandidates protected MapString, Object findAutowireCandidates(Nullable String beanName, Class? requiredType, DependencyDescriptor descriptor) {String[] candidateNames BeanFactoryUtils.beanNamesForTypeIncludingAncestors(this, requiredType, true, descriptor.isEager());MapString, Object result CollectionUtils.newLinkedHashMap(candidateNames.length);for (Map.EntryClass?, Object classObjectEntry : this.resolvableDependencies.entrySet()) {Class? autowiringType classObjectEntry.getKey();if (autowiringType.isAssignableFrom(requiredType)) {Object autowiringValue classObjectEntry.getValue();autowiringValue AutowireUtils.resolveAutowiringValue(autowiringValue, requiredType);if (requiredType.isInstance(autowiringValue)) {result.put(ObjectUtils.identityToString(autowiringValue), autowiringValue);break;}}}for (String candidate : candidateNames) {if (!isSelfReference(beanName, candidate) isAutowireCandidate(candidate, descriptor)) {addCandidateEntry(result, candidate, descriptor, requiredType);}}if (result.isEmpty()) {boolean multiple indicatesMultipleBeans(requiredType);// Consider fallback matches if the first pass failed to find anything...DependencyDescriptor fallbackDescriptor descriptor.forFallbackMatch();for (String candidate : candidateNames) {if (!isSelfReference(beanName, candidate) isAutowireCandidate(candidate, fallbackDescriptor) (!multiple || getAutowireCandidateResolver().hasQualifier(descriptor))) {addCandidateEntry(result, candidate, descriptor, requiredType);}}if (result.isEmpty() !multiple) {// Consider self references as a final pass...// but in the case of a dependency collection, not the very same bean itself.for (String candidate : candidateNames) {if (isSelfReference(beanName, candidate) (!(descriptor instanceof MultiElementDescriptor) || !beanName.equals(candidate)) isAutowireCandidate(candidate, fallbackDescriptor)) {addCandidateEntry(result, candidate, descriptor, requiredType);}}}}return result;}DefaultListableBeanFactory#addCandidateEntry /*** Add an entry to the candidate map: a bean instance if available or just the resolved* type, preventing early bean initialization ahead of primary candidate selection.*/private void addCandidateEntry(MapString, Object candidates, String candidateName,DependencyDescriptor descriptor, Class? requiredType) {if (descriptor instanceof MultiElementDescriptor) {Object beanInstance descriptor.resolveCandidate(candidateName, requiredType, this);if (!(beanInstance instanceof NullBean)) {candidates.put(candidateName, beanInstance);}}else if (containsSingleton(candidateName) || (descriptor instanceof StreamDependencyDescriptor ((StreamDependencyDescriptor) descriptor).isOrdered())) {Object beanInstance descriptor.resolveCandidate(candidateName, requiredType, this);candidates.put(candidateName, (beanInstance instanceof NullBean ? null : beanInstance));}else {candidates.put(candidateName, getType(candidateName));}}DefaultListableBeanFactory#resovleCandidate public Object resolveCandidate(String beanName, Class? requiredType, BeanFactory beanFactory)throws BeansException {return beanFactory.getBean(beanName);}
