Spring Boot 2.0.0 升级到2.4.1 循环依赖问题的解决

目录

Spring Boot 2.0.0 升级到2.4.1 循环依赖问题的解决

描述

分析

第一层原因

第二层原因

第三层原因

第四层原因

第五层原因

第六层原因

第七层原因

最终原因

解决方案

相关各版本的比对

Spring Boot 2.0.0.release + Druid 1.19

Spring Boot 2.4.1 + Druid 1.19

Spring Boot 2.4.1 + Druid 1.2.5

Spring Boot 2.4.1 + Druid 1.2.5 + spring.aop.auto=false

总结

---

Spring Boot 2.0.0 升级到2.4.1 循环依赖问题的解决

描述

在升级Spring boot 2.0.0到2.4.1时出现了循环依赖的报错，报错内容如下：

Error creating bean with name 'test1ServiceImpl': Bean with name 'test1ServiceImpl' has been injected into other beans [test2ServiceImpl] 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.

分析

出问题的代码：

@Service
@Log4j2
public class Test1ServiceImpl implements ITest1Service {

    @Autowired
    private ITest2Service test2Service;

    @Cacheable(cacheNames="getNameById")
    @Override public String getNameById(Integer id) {
        Integer newId = test2Service.getId();
        if(id.equals(newId)){
            return "新张三";
        }else{
            return "张三";
        }
    }

    @Override public List getAllNames() {
        return null;
    }
}


@Service
@Log4j2
public class Test2ServiceImpl implements ITest2Service {
    @Autowired
    private ITest1Service test1Service;

    @Transactional
    @Override public Integer getId() {
        return new Random().nextInt(3);
    }

    @Override public List getAllIds() {
        System.out.println(test1Service.getAllNames());
        return null;
    }
}

表面的问题是Test1Service 和Test2Service 的互相依赖，导致循环依赖了。实际上这种简单的循环依赖，Spring 通过多级缓存的方法已经解决了，因此正常应该不会出现该问题。

通过追踪相关的代码，发现问题的触发点是在org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#doCreateBean的方法里，方法的源码如下：

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

		// Instantiate the bean.
		BeanWrapper instanceWrapper = null;
		if (mbd.isSingleton()) {
			instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
		}
		if (instanceWrapper == null) {
			instanceWrapper = createBeanInstance(beanName, mbd, args);
		}
		final Object bean = instanceWrapper.getWrappedInstance();
		Class beanType = instanceWrapper.getWrappedClass();
		if (beanType != NullBean.class) {
			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;
			}
		}

		// 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.isDebugEnabled()) {
				logger.debug("Eagerly caching bean '" + beanName +
						"' to allow for resolving potential circular references");
			}
			addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
		}

		// Initialize the bean instance.
		Object exposedObject = bean;
		try {
			populateBean(beanName, mbd, instanceWrapper);
			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 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 " +
								"'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;
	}

第一层原因

分析代码发现是exposedObject 和bean不是同一个对象导致的。

相关的代码：

		//判断是否需要暴露早期对象
		if (earlySingletonExposure) {
		   //只读方法获取早期对象（false表示不存在就不创建）,从一级缓存和二级缓存获取
		   //到这一步通常bean都存在，获取到的是增强后的Bean对象
			Object earlySingletonReference = getSingleton(beanName, false);
			if (earlySingletonReference != null) {
			    //如果暴露的Bean仍是原始的Bean
				if (exposedObject == bean) {
				    //替换为增强后的Bean对象
					exposedObject = earlySingletonReference;
				}
				//如果在有增强bean后，不允许原始的Bean注入，并且bean又包含了依赖的Bean
				else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
					//获取依赖的Bean列表
					String[] dependentBeans = getDependentBeans(beanName);
					Set actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
					for (String dependentBean : dependentBeans) {
					    //如果依赖的Bean已创建成功
						if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
						    //增加实际依赖了的Bean
							actualDependentBeans.add(dependentBean);
						}
					}
					//如果实际依赖的Bean不为空，则抛出循环依赖的异常
					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.");
					}
				}
			}
		}

2.0.0版本版本的org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#getSingleton(java.lang.String, boolean)代码：

	protected Object getSingleton(String beanName, boolean allowEarlyReference) {
		Object singletonObject = this.singletonObjects.get(beanName);
		if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
			synchronized (this.singletonObjects) {
				singletonObject = this.earlySingletonObjects.get(beanName);
				if (singletonObject == null && allowEarlyReference) {
					ObjectFactory singletonFactory = this.singletonFactories.get(beanName);
					if (singletonFactory != null) {
						singletonObject = singletonFactory.getObject();
						this.earlySingletonObjects.put(beanName, singletonObject);
						this.singletonFactories.remove(beanName);
					}
				}
			}
		}
		return singletonObject;
	}

2.4.1版本的org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#getSingleton(java.lang.String, boolean)代码：

protected Object getSingleton(String beanName, boolean allowEarlyReference) {
		// Quick check for existing instance without full singleton lock
		Object 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 lock
					singletonObject = 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;
	}

第二层原因

进一步分析exposedObject 和bean为什么不是同一个对象？

相关代码如下：

// Initialize the bean instance.
		//设置暴露的Bean为原始的Bean
		Object exposedObject = bean;
		try {
		    //完善Bean的信息，包括注入依赖的Bean, 则会递归初始化依赖 bean
			populateBean(beanName, mbd, instanceWrapper);
			//完成Bean的创建（包括增强处理）,此时返回的Bean就不是原始的Bean了，而是增强后的Bean
			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);
			}
		}

第三层原因

进一步分析org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#initializeBean(java.lang.String, java.lang.Object, org.springframework.beans.factory.support.RootBeanDefinition) 方法为什么会返回增强后的Bean。发现是applyBeanPostProcessorsAfterInitialization方法返回增强后的Bean。

protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
		if (System.getSecurityManager() != null) {
			AccessController.doPrivileged((PrivilegedAction