帶有@Transactional和@Async的循環(huán)依賴問題的解決
今天我們來探討一個(gè)有意思的spring源碼問題，也是一個(gè)學(xué)生告訴了我現(xiàn)象我從源碼里面找到了這個(gè)有意思的問題。
首先我們看service層的代碼案例，如下：
@Service("transationServiceImpl")
public class TransationServiceImpl implements TransationService {
@Autowired
TransationService transationService;
@Transactional
@Async
@Override
public void transation() {
}
}
在transation方法上面加上了@Transactional和@Async兩個(gè)注解，然后在TransationServiceImpl 類中自己把自己的實(shí)例注入到transationService屬性中，存在循環(huán)依賴，理論上單例的循環(huán)依賴是允許的。但是我們啟動(dòng)容器會(huì)報(bào)錯(cuò)，測試代碼如下：
public class MyTest {
@Test
public void test1() {
AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(ComponentScanBean.class);
}
}
@Component
@ComponentScan(basePackages = {"com.xiangxue"})
public class ComponentScanBean {
}
然后右鍵運(yùn)行test1單元測試加載spring容器就會(huì)報(bào)錯(cuò)，報(bào)錯(cuò)信息如下：
org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name ‘transationServiceImpl': Bean with name ‘transationServiceImpl' has been injected into other beans [transationServiceImpl] 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 ‘a(chǎn)llowEagerInit' flag turned off, for example.
從報(bào)錯(cuò)的字面意思來看，是存在了多版本的循環(huán)依賴，如果要解決這個(gè)問題，我們必須追溯到源碼中。
首先我們從TransationServiceImpl 實(shí)例化開始講起。
實(shí)例化從getBean方法看起，前面代碼我就不貼了，這篇文章是給讀過spring源碼的人看的，沒讀過也看不懂，哈哈 。
1、首先第一次創(chuàng)建TransationServiceImpl實(shí)例的時(shí)候會(huì)從緩存中獲取實(shí)例 ，如果緩存里面有實(shí)例則直接返回，第一次創(chuàng)建的時(shí)候緩存中是沒有實(shí)例的，所以會(huì)走到else代碼塊中。
這里是從三個(gè)緩存中獲取實(shí)例化的詳細(xì)代碼。后面會(huì)分析
@Nullable
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
//根據(jù)beanName從緩存中拿實(shí)例
//先從一級(jí)緩存拿
Object singletonObject = this.singletonObjects.get(beanName);
//如果bean還正在創(chuàng)建，還沒創(chuàng)建完成，其實(shí)就是堆內(nèi)存有了，屬性還沒有DI依賴注入
if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
synchronized (this.singletonObjects) {
//從二級(jí)緩存中拿
singletonObject = this.earlySingletonObjects.get(beanName);
//如果還拿不到，并且允許bean提前暴露
if (singletonObject == null && allowEarlyReference) {
//從三級(jí)緩存中拿到對(duì)象工廠
ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
if (singletonFactory != null) {
//從工廠中拿到對(duì)象
singletonObject = singletonFactory.getObject();
//升級(jí)到二級(jí)緩存
System.out.println("======get instance from 3 level cache->beanName->" + beanName + "->value->" + singletonObject );
this.earlySingletonObjects.put(beanName, singletonObject);
//刪除三級(jí)緩存
this.singletonFactories.remove(beanName);
}
}
}
}
return singletonObject;
}
2、第一次進(jìn)來緩存中沒有則創(chuàng)建TransationServiceImpl的實(shí)例
最終會(huì)走到doCreateBean方法中進(jìn)行實(shí)例化，部分代碼如下
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
............非關(guān)鍵代碼不貼了
// Eagerly cache singletons to be able to resolve circular references
// even when triggered by lifecycle interfaces like BeanFactoryAware.
//是否 單例bean提前暴露
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");
}
//這里著重理解，對(duì)理解循環(huán)依賴幫助非常大，重要程度 5 添加三級(jí)緩存
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
//ioc di，依賴注入的核心方法，該方法必須看，重要程度：5
populateBean(beanName, mbd, instanceWrapper);
//bean 實(shí)例化+ioc依賴注入完以后的調(diào)用，非常重要，重要程度：5
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<>(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.");
}
}
}
}
............非關(guān)鍵代碼不貼了
return exposedObject;
}
由于業(yè)務(wù)類有循環(huán)依賴
所以在第一次實(shí)例化業(yè)務(wù)類的時(shí)候，在populateBean(beanName, mbd, instanceWrapper);進(jìn)行依賴注入時(shí)會(huì)觸發(fā)TransationServiceImpl業(yè)務(wù)類的getBean操作，也就是會(huì)調(diào)用TransationServiceImpl業(yè)務(wù)類的getBean方法，第二次會(huì)走到TransationServiceImpl實(shí)例化的邏輯中。這里明白的刷朵鮮花敲個(gè)1，哈哈。
但是在觸發(fā)第二次業(yè)務(wù)類的getBean操作之前，還有一個(gè)非常重要的步驟，就是業(yè)務(wù)類的提前暴露，也就是三級(jí)緩存的建立。這塊會(huì)建立業(yè)務(wù)類和ObjectFactory的映射關(guān)系這個(gè)建立映射關(guān)系是在依賴注入之前?。。?！
3、循環(huán)依賴注入觸發(fā)TransationServiceImpl類的第二次getBean獲取實(shí)例化的邏輯
第二次進(jìn)來的時(shí)候，由于第一次實(shí)例化的時(shí)候在三級(jí)緩存中建立了映射關(guān)系，所以第二次會(huì)從緩存中獲取實(shí)例
ObjectFactory對(duì)象的getObject方法就會(huì)調(diào)用到。getEarlyBeanReference方法，這個(gè)方法是會(huì)從BeanPostProcessor中獲取實(shí)例，這里可能就會(huì)返回代理實(shí)例
三級(jí)緩存的getObject方法會(huì)調(diào)用到getEarlyBeanReference中，斷點(diǎn)一下，看看。
從斷點(diǎn)看，
3：是獲取事務(wù)代理的BeanPostProcessor類型是SmartInstantiationAwareBeanPostProcessor類型的，所以事務(wù)代理的BeanPostProcessor會(huì)進(jìn)來，然后生成代理
4：是獲取@Async異步代理的BeanPostProcessor，但是不是SmartInstantiationAwareBeanPostProcessor類型的，所以這里if就不會(huì)進(jìn)來，所以最后這里從三級(jí)緩存中拿到的是事務(wù)切面的代碼對(duì)象，注意這里是類中的依賴注入的實(shí)例是事務(wù)切面的代理實(shí)例，如圖：
可以看到，這里的advisors切面容器明顯是一個(gè)事務(wù)切面，所以業(yè)務(wù)類中依賴注入的是一個(gè)事務(wù)切面的代理實(shí)例。
但是在這里我還是要說一下，在生成事務(wù)代理的時(shí)候其實(shí)是有做緩存的，如下代碼：
這里的cacheKey就是TransationServiceImpl業(yè)務(wù)類的bean的名稱的字符串，然后會(huì)把這個(gè)字符串加入到一個(gè)earlyProxyReferences的Set容器中
在這里已經(jīng)在TransationServiceImpl的第二次getBean的時(shí)候從三級(jí)緩存中獲取到了代理對(duì)象了，那么第二次的實(shí)例化已經(jīng)完成了，并且已經(jīng)依賴注入到了TransationServiceImpl的屬性中了，這時(shí)候依賴注入已經(jīng)完成了，好，我們還是接著第一次TransationServiceImpl的實(shí)例來講，貼代碼：
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
............非關(guān)鍵代碼不貼了
// Eagerly cache singletons to be able to resolve circular references
// even when triggered by lifecycle interfaces like BeanFactoryAware.
//是否 單例bean提前暴露
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");
}
//這里著重理解，對(duì)理解循環(huán)依賴幫助非常大，重要程度 5 添加三級(jí)緩存
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
//ioc di，依賴注入的核心方法，該方法必須看，重要程度：5
populateBean(beanName, mbd, instanceWrapper);
//bean 實(shí)例化+ioc依賴注入完以后的調(diào)用，非常重要，重要程度：5
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<>(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.");
}
}
}
}
............非關(guān)鍵代碼不貼了
return exposedObject;
}
也就是populateBean(beanName, mbd, instanceWrapper);依賴注入已經(jīng)完成了，代碼接著往下走。
代理會(huì)執(zhí)行到：
//bean 實(shí)例化+ioc依賴注入完以后的調(diào)用，非常重要，重要程度：5 exposedObject = initializeBean(beanName, exposedObject, mbd);
在這里，業(yè)務(wù)類會(huì)在這個(gè)方法里面再次生成代理，這里就有意思了。代碼如下
protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareMethods(beanName, bean);
return null;
}, getAccessControlContext());
}
else {
//調(diào)用Aware方法
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
//對(duì)類中某些特殊方法的調(diào)用，比如@PostConstruct，Aware接口，非常重要 重要程度 ：5
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
//InitializingBean接口，afterPropertiesSet，init-method屬性調(diào)用,非常重要，重要程度：5
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()) {
//這個(gè)地方可能生出代理實(shí)例，是aop的入口
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
在這個(gè)方法里面可能會(huì)生成業(yè)務(wù)類的代理，我們看看這個(gè)方法：
@Override
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor processor : getBeanPostProcessors()) {
Object current = processor.postProcessAfterInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}
我們斷點(diǎn)看看情況
**效果跟我們預(yù)期的一樣，第一次實(shí)例化的時(shí)候，在屬性依賴注入的時(shí)候會(huì)在三級(jí)緩存中獲取事務(wù)的代理對(duì)象，從斷點(diǎn)看，里面的屬性確實(shí)是一個(gè)事務(wù)的代理對(duì)象，自己本身是沒生成代理的。
由于方法上面有 @Transactional @Async在,3,4兩個(gè)AOP入口的BeanPostProcessor中會(huì)生成相應(yīng)的代理對(duì)象，這里為什么會(huì)生成代理對(duì)象，就不贅述了，核心思想是獲取所有advisors，然后挨個(gè)判斷advisors的pointCut是否matches這兩個(gè)注解，matches的思路是看方法上面是否有@Transactional 或@Async注解，如果有則返回true就匹配了，如果能找到匹配的切面則生成bean的代理，但是這里要注意的是，事務(wù)切面在這里就不會(huì)生成代理了，為什么呢？？？**看代碼
這里會(huì)判斷earlyProxyReferences的Set容器中是否有這個(gè)cacheKey，這個(gè)cacheKey就是類的名稱，而這個(gè)容器在提前暴露的三級(jí)緩存獲取實(shí)例的時(shí)候就已經(jīng)設(shè)置進(jìn)去了，所以Set容器中是有這個(gè)類的
所以3的AOP入口這里會(huì)原樣返回Bean，如圖：
OK，有意思的來了，這時(shí)候就輪到4這個(gè)BeanPostProcessor的異步切面的AOP入口執(zhí)行了。如圖：
在這里就返回了bean的異步切面代理，實(shí)例如圖：
我解釋一下這個(gè)截圖內(nèi)容，
exposedObject是異步代理對(duì)象，在targetSource是代理對(duì)象的目標(biāo)對(duì)象，目標(biāo)對(duì)象中有一個(gè)transationService屬性，這個(gè)屬性是一個(gè)事務(wù)的代理對(duì)象，OK，從這里我們發(fā)現(xiàn)，我去，一個(gè)同樣的類，居然生成了兩個(gè)不同的代理對(duì)象，一個(gè)是異步的代理對(duì)象，一個(gè)是事務(wù)的代理對(duì)象，代理對(duì)象居然不一致了。為什么會(huì)這樣，前面我已經(jīng)分享得很清楚了
然后在spring中，這種情況默認(rèn)是不被允許的，代碼如下：
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 " +
"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
}
}
}
}
Object earlySingletonReference = getSingleton(beanName, false);
這里我們前面分析過，這里會(huì)從三級(jí)緩存中獲取到事務(wù)代理對(duì)象
if (exposedObject == bean) {
exposedObject = earlySingletonReference;
}
然后這里有個(gè)if判斷，bean是第一次實(shí)例化的bean，是沒被initializeBean代理之前的bean
而exposedObject對(duì)象是一個(gè)異步切面的代理對(duì)象
這里兩者是不相等的，而這個(gè)變量默認(rèn)是allowRawInjectionDespiteWrapping=false的
所有這里就會(huì)拋異常，就是文章前面的那個(gè)異常，所有我們找到了為什么會(huì)有這么一個(gè)異常的出現(xiàn)了。
其實(shí)要解決這個(gè)異常也比較簡單，只要把a(bǔ)llowRawInjectionDespiteWrapping這個(gè)屬性變成true就行了。
如何變了，代碼如下：
這是這個(gè)變量就為true了 ，就不會(huì)拋異常了
但是就會(huì)存在一個(gè)現(xiàn)象，單元測試中獲取到的bean對(duì)象和類中依賴注入的對(duì)象不是同一個(gè)了
這個(gè)bean對(duì)象是異步代理對(duì)象
類中屬性的對(duì)象是事務(wù)切面的代理對(duì)象
有意思吧，哈哈 。
如果在類里面沒有@Async異步注解，其實(shí)就不會(huì)有問題，默認(rèn)是允許單例循環(huán)依賴的，為什么沒問題
@Service("transationServiceImpl")
public class TransationServiceImpl implements TransationService {
@Autowired
TransationService transationService;
@Transactional
@Override
public void transation() {
System.out.println(transationService.hashCode());
System.out.println("s");
}
}
因?yàn)?/p>
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 " +
"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
}
}
}
}
如果只要存在循環(huán)依賴，第一次業(yè)務(wù)類實(shí)例化的時(shí)候代理對(duì)象就是從這里獲取的
這個(gè)地方
//bean 實(shí)例化+ioc依賴注入完以后的調(diào)用，非常重要，重要程度：5 exposedObject = initializeBean(beanName, exposedObject, mbd);
由于三級(jí)緩存中建立了緩存了
所以會(huì)直接返回對(duì)應(yīng)的bean，沒有生成代理。代理對(duì)象是從這個(gè)獲取的
是從提前暴露的三級(jí)緩存中獲取的代理對(duì)象賦值給了第一次實(shí)例化的bean對(duì)象，所以這個(gè)else if中可能出現(xiàn)異常的地方就不會(huì)走了，因?yàn)檫@兩個(gè)bean exposedObject 和 bean是相等的。
到此這篇關(guān)于帶有@Transactional和@Async的循環(huán)依賴問題的解決的文章就介紹到這了,更多相關(guān)@Transactional和@Async的循環(huán)依賴內(nèi)容請(qǐng)搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持腳本之家！
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