// 在离线打标服务类中注入审批服务，在“申请打标”时调用public class PortraitOfflineLabelingServiceImpl implements PortraitOfflineLabelingService {        @Resource    private AuditService auditService;
    /** 申请打标 */    Boolean applyOdpsOfflineLabeling(Request request);
    /** 执行打标 */    Boolean executeOdpsOfflineLabeling(Request request);}
// 审批服务类，定义了操作类型-审批回调服务的map映射@Transactional(rollbackFor = Throwable.class)public class AuditServiceImpl implements AuditService,ApplicationContextAware,InitializingBean {        private Map<EntityOperation<?>, AuditCallback> auditCallbackMap = new HashMap<>();
    @Override    public void afterPropertiesSet() throws Exception {        Map<EntityOperation<?>, AuditCallback> auditCallbackMap = new HashMap<>();
        Collection<AuditCallback> beans = applicationContext.getBeansOfType(AuditCallback.class)                .values();
        beans.forEach(auditCallback -> auditCallback.supportBizOperations()                .forEach(item -> auditCallbackMap.put(item, auditCallback)));
        this.auditCallbackMap = auditCallbackMap;    }}
// 在离线打标审批回调类中注入离线打标服务类，用于调用“执行打标”的服务public class OdpsOfflineLabelingCallback implements AuditCallback {
    @Resource    private PortraitOfflineLabelingService offlineLabelingService;
    @Override    public List<EntityOperation<?>> supportBizOperations() {        return Lists.newArrayList(OdpsOfflineLabelingOperation.CREATE_ODPS_OFFLINE_LABELING_INFO);    }}

2.1.1. doGetBean

2.1.1.1. Spring三级缓存

• singletonObjects: 一级缓存，保存实例化&属性注入&初始化完成的bean实例。数据结构是bean名称->bean实例的映射。

• earlySingletonObjects: 二级缓存，用于保存实例化完成，但为属性注入和初始化完成的bean实例。数据结构是bean名称->bean实例的映射。

• singletonFactories: 三级缓存，用于保存bean创建工厂，以便于后面扩展有机会创建代理对象并放入二级缓存。数据结构是bean名称->bean创建工厂的映射。

2.1.1.2. 通过三级缓存获取bean实例

protected Object getSingleton(String beanName, boolean allowEarlyReference) {    // 尝试从一级缓存中获取已经初始化完成的bean实例（完全装载好的bean）    Object singletonObject = this.singletonObjects.get(beanName);    // 如果一级缓存中没有该实例    if (singletonObject == null && this.isSingletonCurrentlyInCreation(beanName)) {        // 跑去二级缓存中获取创建中的实例        singletonObject = this.earlySingletonObjects.get(beanName);        // 如果二级缓存中也没有该实例        if (singletonObject == null && allowEarlyReference) {            // 加锁            synchronized(this.singletonObjects) {                // 二次判断一级缓存和二级缓存中是否存在该实例（加锁时间差）                singletonObject = this.singletonObjects.get(beanName);                if (singletonObject == null) {                    singletonObject = this.earlySingletonObjects.get(beanName);                    if (singletonObject == null) {                        // 还是没有取到实例，尝试从三级缓存中获取创建该实例的工厂                        ObjectFactory<?> singletonFactory = (ObjectFactory)this.singletonFactories.get(beanName);                        if (singletonFactory != null) {                            // 通过工厂获取该实例的单例                            singletonObject = singletonFactory.getObject();                            // 将获取的bean从三级缓存中移除，并且升级到二级缓存中                            this.earlySingletonObjects.put(beanName, singletonObject);                            this.singletonFactories.remove(beanName);                        }                    }                }            }        }    }
    // 返回获取的单例bean    return singletonObject;}

2.1.2. doCreateBean

• createBeanInstance: 实例化Bean，获得未被填充属性的原始Bean。

• populateBean: 如果Bean有需要注入的属性，则进行属性填充，前提是需要填充的属性已经存在于Spring容器中，否则会先加载该属性再进行填充。如果有循环依赖，问题就是在这个过程中发生的。

• initializeBean: 执行bean的初始化过程，包括执行前置方法->执行初始化->执行后置方法。

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)      throws BeanCreationException {
    // 1.实例化bean    // 封装被创建的Bean对象    BeanWrapper instanceWrapper = null;    if (mbd.isSingleton()) {        instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);    }    if (instanceWrapper == null) {        instanceWrapper = createBeanInstance(beanName, mbd, args);    }    // 获取实例化对象的类型    Object bean = instanceWrapper.getWrappedInstance();    Class<?> beanType = instanceWrapper.getWrappedClass();    if (beanType != NullBean.class) {        mbd.resolvedTargetType = beanType;    }
    // 调用PostProcessor后置处理器对bean进行一些操作    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;        }    }
    // 当允许提前暴露时，将实例化好的bean放进singletonFactories三级缓存，用来解决循环依赖导致的问题。    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));    }
    Object exposedObject = bean;    try {        // 2.开始填充bean属性（依赖注入）        populateBean(beanName, mbd, instanceWrapper);        // 3.执行初始化方法（包括前后置的处理器）        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);        }    }
    // 当通过提早暴露解决循环依赖问题时，需要进行单例校验；这里也是本次报错的地方，后面会讲到为啥报错。    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<>(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 " +                            "'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.");                }            }        }    }
    try {        registerDisposableBeanIfNecessary(beanName, bean, mbd);    }    catch (BeanDefinitionValidationException ex) {        throw new BeanCreationException(                mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);    }
    return exposedObject;    }

// 拆分申请打标和执行打标到两个服务中，打破循环依赖public class PortraitApplyOfflineLabelingServiceImpl implements PortraitApplyOfflineLabelingService {        @Resource    private AuditService auditService;
    /** 申请打标 */    Boolean applyOdpsOfflineLabeling(Request request);}
public class PortraitExecuteOfflineLabelingServiceImpl implements PortraitExecuteOfflineLabelingService {
    /** 执行打标 */    Boolean executeOdpsOfflineLabeling(Request request);}

public class OdpsOfflineLabelingCallback implements AuditCallback {
    // 在属性注入的时候增加懒加载的注解    @Lazy    @Resource    private PortraitOfflineLabelingService offlineLabelingService;
    @Override    public List<EntityOperation<?>> supportBizOperations() {        return Lists.newArrayList(OdpsOfflineLabelingOperation.CREATE_ODPS_OFFLINE_LABELING_INFO);    }}

• 创建AuditServiceImpl并填充属性PortraitOfflineLabelingServiceImpl的时候，发现是@Lazy懒注入，则生成一个代理对象直接赋值了，不会再执行去缓存中寻找PortraitOfflineLabelingServiceImpl、找不到再创建的步骤了，而是AuditServiceImpl直接正常走完后续生命周期流程，最终放入单例池。
• 而到单例PortraitOfflineLabelingServiceImpl创建的时候，填充属性AuditServiceImpl时直接能从单例池拿到完整的bean，因此PortraitOfflineLabelingServiceImpl也能正常走完后续生命周期流程。
• 最后，当AuditServiceImpl真正用到懒加载的属性，执行其方法的时候，才会去单例池中寻找真正的bean。

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