自动注入发生的时机：
1、spring refresh invokeBeanFactoryPostProcessors阶段加载 
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
//这里会刷新DefaultListableBeanFactory ，DefaultListableBeanFactory 是 AbstractAutowireCapableBeanFactory 的子类，AbstractAutowireCapableBeanFactory 就是spring IOC容器

2、registerBeanPostProcessors阶段加载
AutowiredAnnotationBeanPostProcessor处理器,核心方法postProcessPropertyValues，提供@Autowired类和方法级别的注入。

	@Override
	public PropertyValues postProcessPropertyValues(
			PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeanCreationException {

		InjectionMetadata metadata = findAutowiringMetadata(beanName, bean.getClass(), pvs);
		try {
			metadata.inject(bean, beanName, pvs);
		}
		catch (BeanCreationException ex) {
			throw ex;
		}
		catch (Throwable ex) {
			throw new BeanCreationException(beanName, "Injection of autowired dependencies failed", ex);
		}
		return pvs;
	}

	private InjectionMetadata findAutowiringMetadata(String beanName, Class<?> clazz, PropertyValues pvs) {
		// Fall back to class name as cache key, for backwards compatibility with custom callers.
		String cacheKey = (StringUtils.hasLength(beanName) ? beanName : clazz.getName());
		// Quick check on the concurrent map first, with minimal locking.
		InjectionMetadata metadata = this.injectionMetadataCache.get(cacheKey);
		if (InjectionMetadata.needsRefresh(metadata, clazz)) {
			synchronized (this.injectionMetadataCache) {
				metadata = this.injectionMetadataCache.get(cacheKey);
				if (InjectionMetadata.needsRefresh(metadata, clazz)) {
					if (metadata != null) {
						metadata.clear(pvs);
					}
					try {
						metadata = buildAutowiringMetadata(clazz);
						this.injectionMetadataCache.put(cacheKey, metadata);
					}
					catch (NoClassDefFoundError err) {
						throw new IllegalStateException("Failed to introspect bean class [" + clazz.getName() +
								"] for autowiring metadata: could not find class that it depends on", err);
					}
				}
			}
		}
		return metadata;
	}

	public void inject(Object target, String beanName, PropertyValues pvs) throws Throwable {
		Collection<InjectedElement> elementsToIterate =
				(this.checkedElements != null ? this.checkedElements : this.injectedElements);
		if (!elementsToIterate.isEmpty()) {
			boolean debug = logger.isDebugEnabled();
			for (InjectedElement element : elementsToIterate) {
				if (debug) {
					logger.debug("Processing injected element of bean '" + beanName + "': " + element);
				}
				element.inject(target, beanName, pvs);
			}
		}
	}

	private InjectionMetadata buildAutowiringMetadata(final Class<?> clazz) {
		LinkedList<InjectionMetadata.InjectedElement> elements = new LinkedList<InjectionMetadata.InjectedElement>();
		Class<?> targetClass = clazz;

		do {
			final LinkedList<InjectionMetadata.InjectedElement> currElements =
					new LinkedList<InjectionMetadata.InjectedElement>();

			ReflectionUtils.doWithLocalFields(targetClass, new ReflectionUtils.FieldCallback() {
				@Override
				public void doWith(Field field) throws IllegalArgumentException, IllegalAccessException {
					AnnotationAttributes ann = findAutowiredAnnotation(field);
					if (ann != null) {
						if (Modifier.isStatic(field.getModifiers())) {
							if (logger.isWarnEnabled()) {
								logger.warn("Autowired annotation is not supported on static fields: " + field);
							}
							return;
						}
						boolean required = determineRequiredStatus(ann);
						currElements.add(new AutowiredFieldElement(field, required));
					}
				}
			});

			ReflectionUtils.doWithLocalMethods(targetClass, new ReflectionUtils.MethodCallback() {
				@Override
				public void doWith(Method method) throws IllegalArgumentException, IllegalAccessException {
					Method bridgedMethod = BridgeMethodResolver.findBridgedMethod(method);
					if (!BridgeMethodResolver.isVisibilityBridgeMethodPair(method, bridgedMethod)) {
						return;
					}
					AnnotationAttributes ann = findAutowiredAnnotation(bridgedMethod);
					if (ann != null && method.equals(ClassUtils.getMostSpecificMethod(method, clazz))) {
						if (Modifier.isStatic(method.getModifiers())) {
							if (logger.isWarnEnabled()) {
								logger.warn("Autowired annotation is not supported on static methods: " + method);
							}
							return;
						}
						if (method.getParameterTypes().length == 0) {
							if (logger.isWarnEnabled()) {
								logger.warn("Autowired annotation should only be used on methods with parameters: " +
										method);
							}
						}
						boolean required = determineRequiredStatus(ann);
						PropertyDescriptor pd = BeanUtils.findPropertyForMethod(bridgedMethod, clazz);
						currElements.add(new AutowiredMethodElement(method, required, pd));
					}
				}
			});

			elements.addAll(0, currElements);
			targetClass = targetClass.getSuperclass();
		}
		while (targetClass != null && targetClass != Object.class);

		return new InjectionMetadata(clazz, elements);
	}

 3、spring refresh finishBeanFactoryInitialization 中 填充Bean属性的时候触发

 org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#populateBean实现

	/**
	 * Populate the bean instance in the given BeanWrapper with the property values
	 * from the bean definition.
	 * @param beanName the name of the bean
	 * @param mbd the bean definition for the bean
	 * @param bw BeanWrapper with bean instance
	 */
	protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
		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;
		}

		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;
                        //核心：这里负责注入执行Autowired的类和方法
						pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
						if (pvs == null) {
							return;
						}
					}
				}
			}
			if (needsDepCheck) {
				checkDependencies(beanName, mbd, filteredPds, pvs);
			}
		}

		applyPropertyValues(beanName, mbd, bw, pvs);
	}