Spring5.0源码深度解析之SpringBean循环依赖问题解决方案

@Service
public class AService {
    //
    @Autowired
    public BService bService;
}

@Service
public class BService {
    @Autowired
    public AService aService;
}

@Scope("prototype")

@Service
@Scope("prototype")
public class AService {
   // @Autowired
    public BService bService;
    // 为什么Aservice在创建的时候 为什么Bservice比ASERVICE 先创建
    public AService() {
        System.out.println("AService被Java的反射技术创建");
    }
    public void setbService(BService bService) {
        this.bService = bService;
    }

}

@Service
@Scope("prototype")
public class BService {
   // @Autowired
    public AService aService;

    public void setaService(AService aService) {
        this.aService = aService;
    }
}

public class SpringApp {
    public static void main(String[] args) {
//        1. ioc容器在创建的时候所有的单例对象是不是会被创建
       AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MyConfig.class);
//        // 对例子情况 当你在调用的时候才获取
        AService aSerivce = applicationContext.getBean("AService", AService.class);
        BService bSerivce = applicationContext.getBean("BService", BService.class);
        aSerivce.setbService(bSerivce);
        bSerivce.setaService(aSerivce);
        // 循环引用异常 找不到对象
        /**
         * 思考问题？ 如果我们的项目对象必须要是多例？ 而且必须要循环引用  明确的指定引用那个对象
         */
        String[] beanDefinitionNames = applicationContext.getBeanDefinitionNames();
        for (int i = 0; i < beanDefinitionNames.length; i++) {
            System.out.println(beanDefinitionNames[i]);
        }

AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MyConfig.class);

// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);

// Instantiate all remaining (non-lazy-init) singletons.
beanFactory.preInstantiateSingletons();

public Object getBean(String name) throws BeansException {
    return this.doGetBean(name, (Class)null, (Object[])null, false);
}

public Object getSingleton(String beanName) {
    return this.getSingleton(beanName, true);
}

protected Object getSingleton(String beanName, boolean allowEarlyReference) {
    Object singletonObject = this.singletonObjects.get(beanName);    //根据BeanName去集合中查，查到就返回这个对象，【】【】【】一级缓存对象集合【】【】【】缓存完整对象【】【】完整对象表示对象已经创建完了，并且对象属性已经赋值了。
    if (singletonObject == null && this.isSingletonCurrentlyInCreation(beanName)) {
        Map var4 = this.singletonObjects;
        synchronized(this.singletonObjects) {
            singletonObject = this.earlySingletonObjects.get(beanName);    //查询二级缓存中是否有缓存对象
            if (singletonObject == null && allowEarlyReference) {
                ObjectFactory<?> singletonFactory = (ObjectFactory)this.singletonFactories.get(beanName);    //查询三级缓存，三级缓存中有的化，将三级缓存中的数据放入二级缓存中
                if (singletonFactory != null) {
                    singletonObject = singletonFactory.getObject();
                    this.earlySingletonObjects.put(beanName, singletonObject);
                    this.singletonFactories.remove(beanName);
                }
            }
        }
    }
    return singletonObject;
}

singletonObject == null && this.isSingletonCurrentlyInCreation(beanName) //一级缓存没有，并且singletonsCurrentlyInCreation判断是否之前标记为该对象开始创建

if (isPrototypeCurrentlyInCreation(beanName)) { //我们对象是单例的，所有不进入
   throw new BeanCurrentlyInCreationException(beanName);
}

public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
   Assert.notNull(beanName, "Bean name must not be null");
   synchronized (this.singletonObjects) {
      Object singletonObject = this.singletonObjects.get(beanName);
      if (singletonObject == null) {
         if (this.singletonsCurrentlyInDestruction) {
            throw new BeanCreationNotAllowedException(beanName,
                  "Singleton bean creation not allowed while singletons of this factory are in destruction " +
                  "(Do not request a bean from a BeanFactory in a destroy method implementation!)");
         }
         if (logger.isDebugEnabled()) {
            logger.debug("Creating shared instance of singleton bean '" + beanName + "'");
         }
         beforeSingletonCreation(beanName);
         boolean newSingleton = false;
         boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
         if (recordSuppressedExceptions) {
            this.suppressedExceptions = new LinkedHashSet<>();
         }
         try {
            singletonObject = singletonFactory.getObject();
            newSingleton = true;
         }
         catch (IllegalStateException ex) {
            // Has the singleton object implicitly appeared in the meantime ->
            // if yes, proceed with it since the exception indicates that state.
            singletonObject = this.singletonObjects.get(beanName);
            if (singletonObject == null) {
               throw ex;
            }
         }
         catch (BeanCreationException ex) {
            if (recordSuppressedExceptions) {
               for (Exception suppressedException : this.suppressedExceptions) {
                  ex.addRelatedCause(suppressedException);
               }
            }
            throw ex;
         }
         finally {
            if (recordSuppressedExceptions) {
               this.suppressedExceptions = null;
            }
            afterSingletonCreation(beanName);
         }
         if (newSingleton) {
            addSingleton(beanName, singletonObject);
         }
      }
      return singletonObject;
   }
}

protected void beforeSingletonCreation(String beanName) {
   if (!this.inCreationCheckExclusions.contains(beanName) && !this.singletonsCurrentlyInCreation.add(beanName)) {
      throw new BeanCurrentlyInCreationException(beanName);
   }
}

populateBean(beanName, mbd, instanceWrapper);//这里给对象属性赋值

protected void addSingletonFactory(String beanName, ObjectFactory<?> singletonFactory) {
   Assert.notNull(singletonFactory, "Singleton factory must not be null");
   synchronized (this.singletonObjects) {
      if (!this.singletonObjects.containsKey(beanName)) {    //【】【】如果一级缓存没有该对象的情况下，会将该对象存放在三级缓存中
         this.singletonFactories.put(beanName, singletonFactory);    //【】【】存放在三级缓存中，对象实例化完成，但是没有赋值，婴儿对象【】【】
         this.earlySingletonObjects.remove(beanName);
         this.registeredSingletons.add(beanName);
      }
   }
}