这一讲分析spring bean属性注入代码populateBean，源码分析如下

    /*** Populate the bean instance in the given BeanWrapper with the property values* from the bean definition.* 丰富bean实例属性*@parambeanName the name of the bean*@parammbd the bean definition for the bean*@parambw BeanWrapper with bean instance*/protected voidpopulateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {PropertyValues pvs=mbd.getPropertyValues();if (bw == null) {if (!pvs.isEmpty()) {throw newBeanCreationException(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.//属性设置前调用处理器boolean continueWithPropertyPopulation = true;if (!mbd.isSynthetic() &&hasInstantiationAwareBeanPostProcessors()) {for(BeanPostProcessor bp : getBeanPostProcessors()) {if (bp instanceofInstantiationAwareBeanPostProcessor) {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= newMutablePropertyValues(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);//设置bean属性if (hasInstAwareBpps ||needsDepCheck) {PropertyDescriptor[] filteredPds=filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);if(hasInstAwareBpps) {for(BeanPostProcessor bp : getBeanPostProcessors()) {if (bp instanceofInstantiationAwareBeanPostProcessor) {InstantiationAwareBeanPostProcessor ibp=(InstantiationAwareBeanPostProcessor) bp;pvs=ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);if (pvs == null) {return;}}}}if(needsDepCheck) {checkDependencies(beanName, mbd, filteredPds, pvs);}}applyPropertyValues(beanName, mbd, bw, pvs);}

debug过程中我们知道，总共有7个BeanPostProcessor

对于@Autowired，@Value注解注入的属性值，AutowiredAnnotationBeanPostProcessor会处理。我们进一步分析AutowiredAnnotationBeanPostProcessor注入属性的代码

    /*** Autowired属性注入*@authorcoshaho *@parampvs*@parampds   注入属性配置，方法中没有使用*@parambean  bean实例*@parambeanName*@return*@throwsBeanCreationException*/publicPropertyValues postProcessPropertyValues(PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName)throwsBeanCreationException {//获取注入属性配置信息InjectionMetadata metadata =findAutowiringMetadata(beanName, bean.getClass(), pvs);try{//属性注入
metadata.inject(bean, beanName, pvs);}catch(BeanCreationException ex) {throwex;}catch(Throwable ex) {throw new BeanCreationException(beanName, "Injection of autowired dependencies failed", ex);}returnpvs;}public void inject(Object target, @Nullable String beanName, @Nullable PropertyValues pvs) throwsThrowable {//获取待注入的属性队列Collection<InjectedElement> checkedElements = this.checkedElements;Collection<InjectedElement> elementsToIterate =(checkedElements!= null ? 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);}//属性注入
element.inject(target, beanName, pvs);}}}

InjectionMetadata是bean注入属性配置，InjectionElement是单个的注入属性配置，InjectionElement.inject则为单个属性注入方法。InjectionElement.inject则调用的DefaultListableBeanFactory.doResolveDependency方法获取属性值

@Overrideprotected void inject(Object bean, @Nullable String beanName, @Nullable PropertyValues pvs) throwsThrowable {Field field= (Field) this.member;Object value;if (this.cached) {value= resolvedCachedArgument(beanName, this.cachedFieldValue);}else{//获取注入属性配置：属性名称，类名称DependencyDescriptor desc = new DependencyDescriptor(field, this.required);desc.setContainingClass(bean.getClass());Set<String> autowiredBeanNames = new LinkedHashSet<>(1);Assert.state(beanFactory!= null, "No BeanFactory available");TypeConverter typeConverter=beanFactory.getTypeConverter();try{//获取属性值value =beanFactory.resolveDependency(desc, beanName, autowiredBeanNames, typeConverter);}catch(BeansException ex) {throw new UnsatisfiedDependencyException(null, beanName, newInjectionPoint(field), ex);}synchronized (this) {if (!this.cached) {if (value != null || this.required) {this.cachedFieldValue =desc;registerDependentBeans(beanName, autowiredBeanNames);if (autowiredBeanNames.size() == 1) {String autowiredBeanName=autowiredBeanNames.iterator().next();if(beanFactory.containsBean(autowiredBeanName)) {if(beanFactory.isTypeMatch(autowiredBeanName, field.getType())) {this.cachedFieldValue = newShortcutDependencyDescriptor(desc, autowiredBeanName, field.getType());}}}}else{this.cachedFieldValue = null;}this.cached = true;}}}if (value != null) {ReflectionUtils.makeAccessible(field);//反射设置属性
field.set(bean, value);}}publicObject resolveDependency(DependencyDescriptor descriptor, @Nullable String requestingBeanName,@Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) throwsBeansException {descriptor.initParameterNameDiscovery(getParameterNameDiscoverer());if (Optional.class ==descriptor.getDependencyType()) {returncreateOptionalDependency(descriptor, requestingBeanName);}else if (ObjectFactory.class == descriptor.getDependencyType() ||ObjectProvider.class ==descriptor.getDependencyType()) {return newDependencyObjectProvider(descriptor, requestingBeanName);}else if (javaxInjectProviderClass ==descriptor.getDependencyType()) {return newJsr330ProviderFactory().createDependencyProvider(descriptor, requestingBeanName);}else{Object result=getAutowireCandidateResolver().getLazyResolutionProxyIfNecessary(descriptor, requestingBeanName);if (result == null) {//获取注入值result =doResolveDependency(descriptor, requestingBeanName, autowiredBeanNames, typeConverter);}returnresult;}}

    publicObject doResolveDependency(DependencyDescriptor descriptor, @Nullable String beanName,@Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) throwsBeansException {//注入属性配置InjectionPoint previousInjectionPoint =ConstructorResolver.setCurrentInjectionPoint(descriptor);try{Object shortcut= descriptor.resolveShortcut(this);if (shortcut != null) {returnshortcut;}//注入属性类型Class<?> type =descriptor.getDependencyType();// 如果是Value注解，这里可以直接获取注解String值Object value=getAutowireCandidateResolver().getSuggestedValue(descriptor);if (value != null) {if (value instanceofString) {String strVal=resolveEmbeddedValue((String) value);BeanDefinition bd= (beanName != null && containsBean(beanName) ? getMergedBeanDefinition(beanName) : null);// Value可以是一个表达式，表达式需要进行计算value=evaluateBeanDefinitionString(strVal, bd);}TypeConverter converter= (typeConverter != null ?typeConverter : getTypeConverter());// 此处对Value进行类型转换return (descriptor.getField() != null ?converter.convertIfNecessary(value, type, descriptor.getField()) :converter.convertIfNecessary(value, type, descriptor.getMethodParameter()));}Object multipleBeans=resolveMultipleBeans(descriptor, beanName, autowiredBeanNames, typeConverter);if (multipleBeans != null) {returnmultipleBeans;}//获取{bean名称：bean类型} Map，bean名称默认为类名称Map<String, Object> matchingBeans =findAutowireCandidates(beanName, type, descriptor);if(matchingBeans.isEmpty()) {if(isRequired(descriptor)) {raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);}return null;}String autowiredBeanName;Object instanceCandidate;if (matchingBeans.size() > 1) {autowiredBeanName=determineAutowireCandidate(matchingBeans, descriptor);if (autowiredBeanName == null) {if (isRequired(descriptor) || !indicatesMultipleBeans(type)) {returndescriptor.resolveNotUnique(type, matchingBeans);}else{//In case of an optional Collection/Map, silently ignore a non-unique case://possibly it was meant to be an empty collection of multiple regular beans//(before 4.3 in particular when we didn't even look for collection beans).return null;}}instanceCandidate=matchingBeans.get(autowiredBeanName);}else{//We have exactly one match.Map.Entry<String, Object> entry =matchingBeans.entrySet().iterator().next();autowiredBeanName=entry.getKey();instanceCandidate=entry.getValue();}if (autowiredBeanNames != null) {autowiredBeanNames.add(autowiredBeanName);}//关键方法，bean名称不为空，通过bean名称，bean类型获取注入beanif (instanceCandidate instanceofClass) {instanceCandidate = descriptor.resolveCandidate(autowiredBeanName, type, this);}Object result=instanceCandidate;if (result instanceofNullBean) {if(isRequired(descriptor)) {raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);}result= null;}if (!ClassUtils.isAssignableValue(type, result)) {throw newBeanNotOfRequiredTypeException(autowiredBeanName, type, instanceCandidate.getClass());}returnresult;}finally{ConstructorResolver.setCurrentInjectionPoint(previousInjectionPoint);}}

这里descriptor.resolveCandidate正好调用了bean创建方法。需要注意的是，autowire注入默认采用bean名称注入，bean名称默认为类名，首字母并不小写。