Spring源码分析（三）（@Autowired实现）

依赖注入的实现： https://blog.csdn.net/qq_37598011/article/details/84451591

    在自动装配中，不需要对Bean属性做显示的依赖注入声明只需要配置autowiring属性，它具体的实现也在依赖注入中的populateBean方法中，Ioc容器会根据这个属性的配置使用反射自动查找属性的类型或者名称，然后根据属性的类型或者名称自动匹配Ioc容器中的Bean，从而完成依赖注入。

AbstractAutowireCapableBeanFactory：

	protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
		//这里取得在BeanDefinition中设置的property值，这些property来自对BeanDefinition的解析
		//具体的解析过程可以参看载入和解析BeanDefinitoin的分析
		PropertyValues pvs = mbd.getPropertyValues();

		if (bw == null) {
			if (!pvs.isEmpty()) {
				throw new BeanCreationException(
						mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
			}
			else {
				// Skip property population phase for null instance.
				return;
			}
		}

		// Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
		// state of the bean before properties are set. This can be used, for example,
		// to support styles of field injection.
		boolean continueWithPropertyPopulation = true;

		if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
			for (BeanPostProcessor bp : getBeanPostProcessors()) {
				if (bp instanceof InstantiationAwareBeanPostProcessor) {
					InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
					if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
						continueWithPropertyPopulation = false;
						break;
					}
				}
			}
		}

		if (!continueWithPropertyPopulation) {
			return;
		}
		//这里对autowire注入的处理，可以根据Bean的名称或者类型来完成Bean的autowire
		if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
				mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
			MutablePropertyValues newPvs = new MutablePropertyValues(pvs);

			// Add property values based on autowire by name if applicable.
			if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
				autowireByName(beanName, mbd, bw, newPvs);
			}

			// Add property values based on autowire by type if applicable.
			if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
				autowireByType(beanName, mbd, bw, newPvs);
			}

			pvs = newPvs;
		}

		boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
		boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE);

		if (hasInstAwareBpps || needsDepCheck) {
			PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
			if (hasInstAwareBpps) {
				for (BeanPostProcessor bp : getBeanPostProcessors()) {
					if (bp instanceof InstantiationAwareBeanPostProcessor) {
						InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
						pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
						if (pvs == null) {
							return;
						}
					}
				}
			}
			if (needsDepCheck) {
				checkDependencies(beanName, mbd, filteredPds, pvs);
			}
		}
		//对属性进行注入
		applyPropertyValues(beanName, mbd, bw, pvs);
	}

     重点是这块代码：如果Bean配置了AUTOWIRE_BY_NAME、AUTOWIRE_BY_TYPE这两个属性则调用对应的方法。例如AUTOWIRE_BY_NAME它首先会根据反射机制从当前Bean中获取需要注入的属性名，然后根据这个属性名从容器中申请同名的Bean，这实际上会触发另一个Bean的生成和依赖注入的过程:

		//这里对autowire注入的处理，可以根据Bean的名称或者类型来完成Bean的autowire
		if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
				mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
			MutablePropertyValues newPvs = new MutablePropertyValues(pvs);

			// Add property values based on autowire by name if applicable.
			if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
				autowireByName(beanName, mbd, bw, newPvs);
			}

			// Add property values based on autowire by type if applicable.
			if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
				autowireByType(beanName, mbd, bw, newPvs);
			}

			pvs = newPvs;
		}

 BeanName:

protected void autowireByName(
			String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {

		String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
		for (String propertyName : propertyNames) {
			if (containsBean(propertyName)) {
				//使用获取的当前Bean的属性名作为Bean的名称，向Ioc容器获取Bean
				//然后把从容器中获取的Bean设置到当前Bean的属性中
				Object bean = getBean(propertyName);
				pvs.add(propertyName, bean);
				registerDependentBean(propertyName, beanName);
				if (logger.isDebugEnabled()) {
					logger.debug("Added autowiring by name from bean name '" + beanName +
							"' via property '" + propertyName + "' to bean named '" + propertyName + "'");
				}
			}
			else {
				if (logger.isTraceEnabled()) {
					logger.trace("Not autowiring property '" + propertyName + "' of bean '" + beanName +
							"' by name: no matching bean found");
				}
			}
		}
	}