spring源码干货分享

记录并分享一下本人学习spring源码的过程，有什么问题或者补充会持续更新。欢迎大家指正！

环境： spring5.X + idea

建议：学习过程中要开着源码一步一步过

Spring根据BeanDefinition创建单例对象

1. DefaultSingletonBeanRegister中getSingleton((String beanName, ObjectFactory<?> singletonFactory))

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, ...);
	}
	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;
  }
}	

解析：

1. getSingleton 方法中还是先要在单例池中获取将要被创建的对象是不是存在，不存在了才去创建。this.singletonObjects.get(beanName); 如果不存在Spring还会效验一下是不是正在被销毁，是则抛异常。this.singletonsCurrentlyInDestruction
2. 一系列效验完成后开始正式创建对象的第一步beforeSingletonCreation(beanName);
   创建对象前要满足俩个条件inCreationCheckExclusions&&singletonsCurrentlyInCreation.add(beanName),当前这个Bean没有被排除，并且这个bean正在创建中。
3. 通过singletonFactory.getObject();回调createBean(beanName, mbd, args);
   创建对象时先获取对应的BeanClass（通过反射创建对象），调用doCreateBean(beanName, mbdToUse, args);，这个方法中才是正儿八经的实例化对象

 protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
  	throws BeanCreationException {
  // Instantiate the bean.
  BeanWrapper instanceWrapper = null;
  //....
  if (instanceWrapper == null) {
  	instanceWrapper = createBeanInstance(beanName, mbd, args);
  }
  Object bean = instanceWrapper.getWrappedInstance();
  Class<?> beanType = instanceWrapper.getWrappedClass();
  if (beanType != NullBean.class) {
  	mbd.resolvedTargetType = beanType;
  }
  //.............
  // 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<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 " +
  						"'getBeanNamesForType' 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;
}

doCreateBean解析：

A. 创建对象：createBeanInstance(beanName, mbd, args);

1. 通过工厂方法创建对象

  if (mbd.getFactoryMethodName() != null) {
      return instantiateUsingFactoryMethod(beanName, mbd, args);
  }

2. 通过默认的无参构造创建对象

  instantiateBean(beanName, mbd);

B. 填充属性：populateBean(beanName, mbd, instanceWrapper); 也是就是Set注入(构造注入已经在创建对象时执行了，自动注入可以忽略)

1. 注解属性赋值

	if (hasInstAwareBpps) {
		if (pvs == null) {
			pvs = mbd.getPropertyValues();
		}
		for (BeanPostProcessor bp : getBeanPostProcessors()) {
			if (bp instanceof InstantiationAwareBeanPostProcessor) {
				InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
				PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
				if (pvsToUse == null) {
					if (filteredPds == null) {
						filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
					}
					pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
					if (pvsToUse == null) {
						return;
					}
				}
				pvs = pvsToUse;
			}
		}
	}

解析：通过注解对属性填充使用了AutowiredAnnotationBeanPostProcessor实现所有操作，在postProcessProperties(pvs, bw.getWrappedInstance(), beanName);方法中真正实现。

2. 标签方式属性赋值

  if (pvs != null) {
    applyPropertyValues(beanName, mbd, bw, pvs);
  }

解析：从RootBeanDefinition中获取属性的List封装到PropertyValues中。
遍历ProperValues 把每个属性的值进行类型转换，最后再给bw设置得到的属性值。-> BeanWrapper.setProperValues(new MutablePropertyValues(deepCopy))。
自定义类型会通过beanFactory.getBean() 获取对应的对象，再走一遍doGetBean() -> createBean() -> doCreateBean()...
（JDK的类型会先封装TypeStringValues。自定义的类型会封装RuntimeBeanReference）

C. 初始化对象：initializeBean(beanName, exposedObject, mbd);

protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
	if (System.getSecurityManager() != null) {
		.......
	}
	else {
		invokeAwareMethods(beanName, bean);
	}
	Object wrappedBean = bean;
	if (mbd == null || !mbd.isSynthetic()) {
		wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
	}
	try {
		invokeInitMethods(beanName, wrappedBean, mbd);
	}
	catch (Throwable ex) {
		......
	}
	if (mbd == null || !mbd.isSynthetic()) {
		wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
	}
	return wrappedBean;
}

解析：初始化分几个功能
1. Aware -> invokeAwareMethods(String beanName, Object bean)。spring提供的帮助我们获取Spring容器中对应的组件的相关信息。
2. BeanPostProcessorsBefore -> applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);已经创建好的对象初始化之前再次加工。
3. 初始化 -> invokeInitMethods(beanName, wrappedBean, mbd);包含了接口初始化((InitializingBean) bean).afterPropertiesSet();和自定义方法初始化invokeCustomInitMethod(beanName, bean, mbd);
4. BeanPostProcessorsAfter -> applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);已经创建好的对象初始化之后再次加工。

最后

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