Spring探秘之循环依赖的解决（二）：源码分析

@Service
public class Service1 {

    @Autowired
    private Service2 service2;

    public Service1() {
        System.out.println("service1Ĺ췽");
    }

    /**
     * ע @AopAnnotation ˣҪ
     */
    @AopAnnotation
    public void printAutowired() {
        System.out.println("Service1 Autowired:" + service2.getClass());
    }

    @Override
    public String toString() {
        return "Service1:" + getClass();
    }
}

@Component
public class Service2 {

    @Autowired
    private Service1 service1;

    public Service2() {
        System.out.println("service2Ĺ췽");
    }

    /**
     * ע @AopAnnotation ˣҪ
     */
    @AopAnnotation
    public void printAutowired() {
        System.out.println("Service2 Autowired:" + service1.getClass());
    }

    @Override
    public String toString() {
        return "Service2:" + this.getClass();
    }
}

public class Demo03Main {

    public static void main(String[] args) {
        ApplicationContext context = 
                new AnnotationConfigApplicationContext(AopAnnotationConfig.class);
        Object obj1 = context.getBean("service1");
        Object obj2 = context.getBean("service2");
        ((Service1)obj1).printAutowired();
        ((Service2)obj2).printAutowired();
    }
}

service1Ĺ췽
service2Ĺ췽
Disconnected from the target VM, address: 'localhost:55518', transport: 'socket'
Connected to the target VM, address: '127.0.0.1:55507', transport: 'socket'
@Around: before execute...
Service1 Autowired:class org.springframework.learn.explore.demo03.Service2$$EnhancerBySpringCGLIB$$e7e367ab
@Around: after execute...
@Around: before execute...
Service2 Autowired:class org.springframework.learn.explore.demo03.Service1$$EnhancerBySpringCGLIB$$d447df08
@Around: after execute...

|-AbstractBeanFactory#getBean(String)
 |-AbstractBeanFactory#doGetBean

    protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
            @Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {

        ...
        // 1\. ǷѳʼbeanNamesingletonsCurrentlyInCreation
        Object sharedInstance = getSingleton(beanName);
        ...
        // ǵ
        if (mbd.isSingleton()) {
            // 2\. getSingleton(): ɾ
            sharedInstance = getSingleton(beanName, () -> {
                try {
                    // ִд Bean
                    return createBean(beanName, mbd, args);
                }
                catch (BeansException ex) {
                    destroySingleton(beanName);
                    throw ex;
                }
            });
            // ͨBean Ļֱӷأ FactoryBean Ļ
            // Ǹʵ
            bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
        }
        ...
    }

|-AbstractBeanFactory#getBean(String)
 |-AbstractBeanFactory#doGetBean
  |-DefaultSingletonBeanRegistry#getSingleton(String)
   |-DefaultSingletonBeanRegistry#getSingleton(String, boolean)

/*
 * beanName: ֵΪ service1
 * allowEarlyReferenceֵΪ true
 */
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
    // 1\. һлȡǻȡ
    Object singletonObject = this.singletonObjects.get(beanName);
    // 2\. isSingletonCurrentlyInCreation(...) жservice1ǷڴУ false
    if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
        // ʡĴ
        ...
    }
    return singletonObject;
}

    /**
     * beanNameservice1
     * singletonFactorylambdaʽֵΪ
     *           () -> {
     *               try {
     *                   // Ǵbean
     *                   return createBean(beanName, mbd, args);
     *               }
     *               catch (BeansException ex) {
     *                   destroySingleton(beanName);
     *                   throw ex;
     *               }
     *           }
     */
    public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
        Assert.notNull(beanName, "Bean name must not be null");
        synchronized (this.singletonObjects) {
            // ٴжbeanǷѴ
            Object singletonObject = this.singletonObjects.get(beanName);
            if (singletonObject == null) {
                // 1\. жϵǰʵbeanǷڴ
                // beanNameӵ singletonsCurrentlyInCreation 
                beforeSingletonCreation(beanName);
                try {
                    // 2\. beanĴ
                    singletonObject = singletonFactory.getObject();
                }
                catch (...) {
                    ...
                }
                ...
            }
            return singletonObject;
        }
    }

() -> {
    try {
        // ִд Bean
        return createBean(beanName, mbd, args);
    }
    catch (BeansException ex) {
        destroySingleton(beanName);
        throw ex;
    }
}

|-AbstractBeanFactory#getBean(String)
 |-AbstractBeanFactory#doGetBean
  |-DefaultSingletonBeanRegistry#getSingleton(String, ObjectFactory<?>)
   |-AbstractAutowireCapableBeanFactory#createBean(String, RootBeanDefinition, Object[])
    |-AbstractAutowireCapableBeanFactory#doCreateBean

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

    BeanWrapper instanceWrapper = null;
    if (instanceWrapper == null) {
        // 1\. ʵ Beanjavaʵ
        instanceWrapper = createBeanInstance(beanName, mbd, args);
    }
    //beanʵ
    final Object bean = instanceWrapper.getWrappedInstance();
    //bean
    Class<?> beanType = instanceWrapper.getWrappedClass();
    if (beanType != NullBean.class) {
        mbd.resolvedTargetType = beanType;
    }

    synchronized (mbd.postProcessingLock) {
        if (!mbd.postProcessed) {
            try {
                //  AutowiredAnnotationBeanPostProcessor#postProcessMergedBeanDefinition 
                // 2\. ȡҪע뷽ע @Autowired ע⣩
                applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
            }
            catch (Throwable ex) {
                throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                        "Post-processing of merged bean definition failed", ex);
            }
            mbd.postProcessed = true;
        }
    }
    // ѭ, Ƿѭ, allowCircularReferencesĬΪtrueԹر
    boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
            isSingletonCurrentlyInCreation(beanName));
    if (earlySingletonExposure) {
        // 3\.  bean ӵ singletonFactories
        addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
    }

    Object exposedObject = bean;
    try {
        // 4\. ע룬Ҫע service2Ȼٵ getBean("service2")
        populateBean(beanName, mbd, instanceWrapper);
        ...
    }
    catch (Throwable ex) {
        ...
    }
}

protected void addSingletonFactory(String beanName, ObjectFactory<?> singletonFactory) {
    Assert.notNull(singletonFactory, "Singleton factory must not be null");
    synchronized (this.singletonObjects) {
        // صвڲŻadd
        if (!this.singletonObjects.containsKey(beanName)) {
            // ѹputsingletonFactories
            this.singletonFactories.put(beanName, singletonFactory);
            // ɾеĶ
            this.earlySingletonObjects.remove(beanName);
            this.registeredSingletons.add(beanName);
        }
    }
}

    protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
            @Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {

        ...
        // 1\. ǷѳʼbeanNamesingletonsCurrentlyInCreation
        Object sharedInstance = getSingleton(beanName);
        ...
}

/*
 * beanName: ֵΪ service1
 * allowEarlyReferenceֵΪ true
 */
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
    // 1\. һлȡǻȡ
    Object singletonObject = this.singletonObjects.get(beanName);
    // 2\. isSingletonCurrentlyInCreation(...) жservice1ǷڴУ true
    if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
            synchronized (this.singletonObjects) {
                // 3\. ӶлȡҲȡ
                singletonObject = this.earlySingletonObjects.get(beanName);
                // 4\. allowEarlyReferencetrueִ
                if (singletonObject == null && allowEarlyReference) {
                    // 5\. лȡܻȡ
                    ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
                    if (singletonFactory != null) {
                        // 6\.  singletonFactory.getObject()
                        // յõ AbstractAutowireCapableBeanFactory.getEarlyBeanReference 
                        singletonObject = singletonFactory.getObject();
                        // 7\. 
                        // ŵ
                        this.earlySingletonObjects.put(beanName, singletonObject);
                        // 
                        this.singletonFactories.remove(beanName);
                    }
                }
            }
    }
    return singletonObject;
}

protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {
    Object exposedObject = bean;
    if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
        for (BeanPostProcessor bp : getBeanPostProcessors()) {
            if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
                // úôaop
                SmartInstantiationAwareBeanPostProcessor ibp = 
                      (SmartInstantiationAwareBeanPostProcessor) bp;
                //  `AbstractAutoProxyCreator#getEarlyBeanReference`ǰ aop
                exposedObject = ibp.getEarlyBeanReference(exposedObject, beanName);
            }
        }
    }
    return exposedObject;
}

public Object getEarlyBeanReference(Object bean, String beanName) {
    Object cacheKey = getCacheKey(bean.getClass(), beanName);
    this.earlyProxyReferences.put(cacheKey, bean);
    // ɴ
    return wrapIfNecessary(bean, beanName, cacheKey);
}

aop ̣ɲο [spring aop ֮ AnnotationAwareAspectJAutoProxyCreator £](https://my.oschina.net/funcy/blog/4687961)Ͳٷˡִ `AbstractAutoProxyCreator#getEarlyBeanReference` ֮5 ṹе£

protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
        @Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
    ...

    // Ƿѳʼ
    Object sharedInstance = getSingleton(beanName);

    // 1\. ܻȡif Ĵִ
    if (sharedInstance != null && args == null) {
        // 2\. ͨBean Ļֱӷأ FactoryBean ĻǸʵ
        // beanservice1Ĵ
        bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
    } else {
        // Ĵ벻ִеͲ
        ...
    }

    // beanתﷵfalseִе
    if (requiredType != null && !requiredType.isInstance(bean)) {
    ...
    }

    // 3\. ش`getSingleton(beanName)`õĶ
    return bean;

}

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

        // Ĵ 3.2 ѾˣͲٷ
        ...

        Object exposedObject = bean;
        try {
            // 1\. װ, Ҳdz˵ע
            populateBean(beanName, mbd, instanceWrapper);
            // 2\. ʼᴦ aop 
            exposedObject = initializeBean(beanName, exposedObject, mbd);
        }
        catch (Throwable ex) {
            ...
        }

        //ͬģѭ
        if (earlySingletonExposure) {
            // 3\. ӻлȡ beanName Ӧbean
            Object earlySingletonReference = getSingleton(beanName, false);
            // 4\. earlySingletonReference Ϊ nullif ݲִ
            if (earlySingletonReference != null) {
                ...
            }
        }

        // ʡԲҪĴ
        ...

        return exposedObject;
    }

public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
    Assert.notNull(beanName, "Bean name must not be null");
    synchronized (this.singletonObjects) {
        ...
            try {
                // 1\. beanĴ
                singletonObject = singletonFactory.getObject();
                newSingleton = true;
            }
            catch (...) {
                ...
            }
            finally {
                ...
                // 2\. ɺһЩ
                //  service2  singletonsCurrentlyInCreation Ƴ
                afterSingletonCreation(beanName);
            }
            if (newSingleton) {
                // 3\. öӵ beanFactory Уɾ
                addSingleton(beanName, singletonObject);
            }
        ...
        return singletonObject;
    }
}

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

        // Ĵ 3.1 ѾˣͲٷ
        ...

        Object exposedObject = bean;
        try {
            // 1\. װ, Ҳdz˵ע
            populateBean(beanName, mbd, instanceWrapper);
            // 2\. ʼᴦ aop 
            exposedObject = initializeBean(beanName, exposedObject, mbd);
        }
        catch (Throwable ex) {
            ...
        }

        //ͬģѭ
        if (earlySingletonExposure) {
            // 3\. ӻлȡ beanName Ӧbean
            Object earlySingletonReference = getSingleton(beanName, false);
            // 4\. earlySingletonReference Ϊ nullif ݻִ
            if (earlySingletonReference != null) {
                if (exposedObject == bean) {
                    // 5\. صĶֵ exposedObjectضΪ
                    exposedObject = earlySingletonReference;
                }
            }
        }

        // ʡԲҪĴ
        ...

        return exposedObject;
    }