有代理对象的循环依赖

changelog.md

@@ -1449,6 +1449,9 @@ A依赖B，B又依赖A，循环依赖。容器加载时会执行依赖流程：
 
 下一节填坑。
 
+## 解决循环依赖问题（二）：有代理对象
+> 分支：circular-reference-with-proxy-bean
+
 
 
 

src/main/java/org/springframework/aop/framework/autoproxy/DefaultAdvisorAutoProxyCreator.java

@@ -13,6 +13,8 @@
 import org.springframework.beans.factory.support.DefaultListableBeanFactory;
 
 import java.util.Collection;
+import java.util.HashSet;
+import java.util.Set;
 
 /**
  * @author derekyi
@@ -22,8 +24,24 @@ public class DefaultAdvisorAutoProxyCreator implements InstantiationAwareBeanPos
 
 	private DefaultListableBeanFactory beanFactory;
 
+	private Set<Object> earlyProxyReferences = new HashSet<>();
+
 	@Override
 	public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
+		if (!earlyProxyReferences.contains(beanName)) {
+			return wrapIfNecessary(bean, beanName);
+		}
+
+		return bean;
+	}
+
+	@Override
+	public Object getEarlyBeanReference(Object bean, String beanName) throws BeansException {
+		earlyProxyReferences.add(beanName);
+		return wrapIfNecessary(bean, beanName);
+	}
+
+	protected Object wrapIfNecessary(Object bean, String beanName) {
 		//避免死循环
 		if (isInfrastructureClass(bean.getClass())) {
 			return bean;

src/main/java/org/springframework/beans/factory/ObjectFactory.java

@@ -0,0 +1,12 @@
+package org.springframework.beans.factory;
+
+import org.springframework.beans.BeansException;
+
+/**
+ * @author derekyi
+ * @date 2021/1/30
+ */
+public interface ObjectFactory<T> {
+
+	T getObject() throws BeansException;
+}

src/main/java/org/springframework/beans/factory/config/InstantiationAwareBeanPostProcessor.java

@@ -40,4 +40,17 @@ public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {
 	 */
 	PropertyValues postProcessPropertyValues(PropertyValues pvs, Object bean, String beanName)
 			throws BeansException;
+
+	/**
+	 * 提前暴露bean
+	 *
+	 * @param bean
+	 * @param beanName
+	 * @return
+	 * @throws BeansException
+	 */
+	default Object getEarlyBeanReference(Object bean, String beanName) throws BeansException {
+		return bean;
+	}
+
 }

src/main/java/org/springframework/beans/factory/support/AbstractAutowireCapableBeanFactory.java

@@ -10,6 +10,7 @@
 import org.springframework.beans.factory.BeanFactoryAware;
 import org.springframework.beans.factory.DisposableBean;
 import org.springframework.beans.factory.InitializingBean;
+import org.springframework.beans.factory.ObjectFactory;
 import org.springframework.beans.factory.config.*;
 import org.springframework.core.convert.ConversionService;
 
@@ -70,7 +71,13 @@ protected Object doCreateBean(String beanName, BeanDefinition beanDefinition) {
 
 			//为解决循环依赖问题，将实例化后的bean放进缓存中提前暴露
 			if (beanDefinition.isSingleton()) {
-				earlySingletonObjects.put(beanName, bean);
+				Object finalBean = bean;
+				addSingletonFactory(beanName, new ObjectFactory<Object>() {
+					@Override
+					public Object getObject() throws BeansException {
+						return getEarlyBeanReference(beanName, beanDefinition, finalBean);
+					}
+				});
 			}
 
 			//实例化bean之后执行
@@ -92,11 +99,27 @@ protected Object doCreateBean(String beanName, BeanDefinition beanDefinition) {
 		registerDisposableBeanIfNecessary(beanName, bean, beanDefinition);
 
 		if (beanDefinition.isSingleton()) {
-			addSingleton(beanName, bean);
+			//如果有代理对象，此处获取代理对象
+			Object exposedObject = getSingleton(beanName);
+			addSingleton(beanName, exposedObject);
 		}
 		return bean;
 	}
 
+	protected Object getEarlyBeanReference(String beanName, BeanDefinition beanDefinition, Object bean) {
+		Object exposedObject = bean;
+		for (BeanPostProcessor bp : getBeanPostProcessors()) {
+			if (bp instanceof InstantiationAwareBeanPostProcessor) {
+				exposedObject = ((InstantiationAwareBeanPostProcessor) bp).getEarlyBeanReference(exposedObject, beanName);
+				if (exposedObject == null) {
+					return exposedObject;
+				}
+			}
+		}
+
+		return exposedObject;
+	}
+
 	/**
 	 * bean实例化后执行，如果返回false，不执行后续设置属性的逻辑
 	 *

src/main/java/org/springframework/beans/factory/support/DefaultSingletonBeanRegistry.java

@@ -2,10 +2,10 @@
 
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.DisposableBean;
+import org.springframework.beans.factory.ObjectFactory;
 import org.springframework.beans.factory.config.SingletonBeanRegistry;
 
 import java.util.HashMap;
-import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Set;
 
@@ -15,26 +15,44 @@
  */
 public class DefaultSingletonBeanRegistry implements SingletonBeanRegistry {
 
+	//一级缓存
 	private Map<String, Object> singletonObjects = new HashMap<>();
 
-	protected Map<String, Object> earlySingletonObjects = new HashMap<>();
+	//二级缓存
+	private Map<String, Object> earlySingletonObjects = new HashMap<>();
+
+	//三级缓存
+	private Map<String, ObjectFactory<?>> singletonFactories = new HashMap<String, ObjectFactory<?>>();
 
 	private final Map<String, DisposableBean> disposableBeans = new HashMap<>();
 
 	@Override
 	public Object getSingleton(String beanName) {
-		Object bean = singletonObjects.get(beanName);
-		if (bean == null) {
-			bean = earlySingletonObjects.get(beanName);
+		Object singletonObject = singletonObjects.get(beanName);
+		if (singletonObject == null) {
+			singletonObject = earlySingletonObjects.get(beanName);
+			if (singletonObject == null) {
+				ObjectFactory<?> singletonFactory = singletonFactories.get(beanName);
+				if (singletonFactory != null) {
+					singletonObject = singletonFactory.getObject();
+					//从三级缓存放进二级缓存
+					earlySingletonObjects.put(beanName, singletonObject);
+					singletonFactories.remove(beanName);
+				}
+			}
 		}
-		return bean;
+		return singletonObject;
 	}
 
 	@Override
 	public void addSingleton(String beanName, Object singletonObject) {
 		singletonObjects.put(beanName, singletonObject);
 	}
 
+	protected void addSingletonFactory(String beanName, ObjectFactory<?> singletonFactory) {
+		singletonFactories.put(beanName, singletonFactory);
+	}
+
 	public void registerDisposableBean(String beanName, DisposableBean bean) {
 		disposableBeans.put(beanName, bean);
 	}

src/test/java/org/springframework/test/ioc/CircularReferenceWithProxyBeanTest.java

@@ -19,8 +19,6 @@ public void testCircularReference() throws Exception {
 		A a = applicationContext.getBean("a", A.class);
 		B b = applicationContext.getBean("b", B.class);
 
-		//增加二级缓存不能解决有代理对象时的循环依赖。
-		//a被代理，放进二级缓存earlySingletonObjects中的是实例化后的A，而放进一级缓存singletonObjects中的是被代理后的A，实例化b时从earlySingletonObjects获取a，所以b.getA() != a
-		assertThat(b.getA() != a).isTrue();
+		assertThat(b.getA() == a).isTrue();
 	}
 }