正文
doCreateBean() 主要用于完成 bean 的创建和初始化工作，我们可以将其分为四个过程：
1、createBeanInstance() 实例化 bean/
2、populateBean() 属性填充
3、循环依赖的处理/
4、initializeBean() 初始化 bean
protectedvoidpopulateBean(String beanName, RootBeanDefinition mbd,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 propertypopulation phase for null instance.
return;
}
}
// Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
// state of thebean before properties are set. This canbe used, for example,
// to support styles offieldinjection.
boolean continueWithPropertyPopulation = true;
if(!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if(bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor)bp;
//返回值为是否继续填充bean
if(!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
continueWithPropertyPopulation = false;
break;
}
}
}
}
//如果后处理器发出停止填充命令则终止后续的执行
if(!continueWithPropertyPopulation) {
return;
}
if(mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME||
mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
//Add property valuesbased on autowireby nameifapplicable.
//根据名称自动注入
if(mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
autowireByName(beanName, mbd,bw, newPvs);
}
//Add property valuesbased on autowireby typeifapplicable.
//根据类型自动注入
if(mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
autowireByType(beanName, mbd,bw, newPvs);
}
pvs = newPvs;
}
//后处理器已经初始化
boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
//需要依赖检查
boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
//需要依赖检查
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;
//对所有需要依赖检查的属性进行后处理
pvs = ibp.postProcessPropertyValues(pvs, filteredPds,bw.getWrappedInstance(), beanName);
if(pvs == null) {
return; } } } }
if(needsDepCheck) {
//依赖检查，对应depends-on属性，3.0已经弃用此属性
checkDependencies(beanName, mbd, filteredPds, pvs); }
}
//将属性应用到bean中
//将所有ProtertyValues中的属性填充至BeanWrapper中。
applyPropertyValues(beanName, mbd,bw, pvs);
}
我们详细分析下populateBean的流程：
（1）首先进行属性是否为空的判断
（2）通过调用InstantiationAwareBeanPostProcessor的postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)方法来控制程序是否继续进行属性填充
（3）根据注入类型（byName/byType）提取依赖的bean，并统一存入PropertyValues中
（4）应用InstantiationAwareBeanPostProcessor的postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName)方法，对属性获取完毕填充前的再次处理，典型的应用是RequiredAnnotationBeanPostProcesser类中对属性的验证
（5）将所有的PropertyValues中的属性填充至BeanWrapper中
上面步骤中有几个地方是我们比较感兴趣的，它们分别是依赖注入（autowireByName/autowireByType）以及属性填充，接下来进一步分析这几个功能的实现细节
自动注入
Spring 会根据注入类型（ byName / byType ）的不同，调用不同的方法（autowireByName() / autowireByType()）来注入属性值。
autowireByName()
protectedvoid autowireByName(String beanName, AbstractBeanDefinition mbd,BeanWrapper bw, MutablePropertyValues pvs) {
// 获取Bean 对象中非简单属性
String[] propertyNames = unsatisfiedNonSimpleProperties(mbd,bw);
for (String propertyName : propertyNames) {
// 如果容器中包含指定名称的bean，则将该 bean 注入到bean中
if(containsBean(propertyName)) {
// 递归初始化相关beanObjectbean = getBean(propertyName);
// 为指定名称的属性赋予属性值 pvs.add(propertyName, bean);
// 属性依赖注入
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");}
}
}
}
该方法逻辑很简单，获取该 bean 的非简单属性，什么叫做非简单属性呢？就是类型为对象类型的属性，但是这里并不是将所有的对象类型都都会找到，比如 8 个原始类型，String 类型 ，Number类型、Date类型、URL类型、URI类型等都会被忽略，如下：
protectedString[] unsatisfiedNonSimpleProperties(AbstractBeanDefinitionmbd,BeanWrapperbw) {
Set result =newTreeSet<>();
PropertyValuespvs=mbd.getPropertyValues();
PropertyDescriptor[]pds=bw.getPropertyDescriptors();
for(PropertyDescriptorpd : pds) {
if(pd.getWriteMethod() !=null&& !isExcludedFromDependencyCheck(pd) && !pvs.contains(pd.getName()) && !BeanUtils.isSimpleProperty(pd.getPropertyType())) {result.add(pd.getName());
}
}
returnStringUtils.toStringArray(result);
}
这里获取的就是需要依赖注入的属性。
autowireByName()函数的功能就是根据传入的参数中的pvs中找出已经加载的bean，并递归实例化，然后加入到pvs中
autowireByType
autowireByType与autowireByName对于我们理解与使用来说复杂程度相似，但是实现功能的复杂度却不一样，我们看下方法代码：
protectedvoidautowireByType(StringbeanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) { TypeConverter converter = getCustomTypeConverter();
if(converter ==null) {
converter = bw;
}
Set autowiredBeanNames =newLinkedHashSet(4);
//寻找bw中需要依赖注入的属性
String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
for(StringpropertyName : propertyNames) {
try{ PropertyDescriptor pd = bw.getPropertyDescriptor(propertyName);
// Don't try autowiring by type for type Object: never makes sense,
// even if it technically is a unsatisfied, non-simple property.
if(!Object.class.equals(pd.getPropertyType())) {
//探测指定属性的set方法
MethodParameter methodParam = BeanUtils.
getWriteMethodParameter(pd);
// Do not allow eager init for type matching in case of a prioritized post-processor. booleaneager = !PriorityOrdered.class.isAssignableFrom(bw.getWrappedClass());
DependencyDescriptor desc =newAutowireByTypeDependencyDescriptor(methodParam, eager);
//解析指定beanName的属性所匹配的值，并把解析到的属性名称存储在autowiredBeanNames中，
ObjectautowiredArgument = resolveDependency(desc, beanName, autowiredBeanNames, converter);
if(autowiredArgument !=null) {
pvs.add(propertyName, autowiredArgument);
}for(StringautowiredBeanName : autowiredBeanNames) {
//注册依赖 registerDependentBean(autowiredBeanName, beanName);
if(logger.isDebugEnabled()) {
logger.debug("Autowiring by type from bean name '"+ beanName +"' via property '"+ propertyName +"' to bean named '"+ autowiredBeanName +"'");
}
} autowiredBeanNames.clear();
}
}catch(BeansException ex) {
thrownewUnsatisfiedDependencyException(mbd.getResourceDescription(), beanName, propertyName, ex);
}
}
}
根据名称第一步与根据属性第一步都是寻找bw中需要依赖注入的属性，然后遍历这些属性并寻找类型匹配的bean,其中最复杂就是寻找类型匹配的bean。spring中提供了对集合的类型注入支持，如使用如下注解方式：
@AutowiredprivateList tests;
这种方式spring会把所有与Test匹配的类型找出来并注入到tests属性中，正是由于这一因素，所以在autowireByType函数，新建了局部遍历autowireBeanNames，用于存储所有依赖的bean，如果只是对非集合类的属性注入来说，此属性并无用处。
对于寻找类型匹配的逻辑实现是封装在了resolveDependency函数中，其实现如下：
publicObjectresolveDependency(DependencyDescriptor descriptor,StringbeanName, Set autowiredBeanNames, TypeConverter typeConverter) throws BeansException { descriptor.initParameterNameDiscovery(getParameterNameDiscoverer());
if(descriptor.getDependencyType().equals(ObjectFactory.class)) {
//ObjectFactory类注入的特殊处理
returnnewDependencyObjectFactory(descriptor, beanName);
}else if(descriptor.getDependencyType().equals(javaxInjectProviderClass)) {
//javaxInjectProviderClass类注入的特殊处理
returnnewDependencyProviderFactory().createDependencyProvider(descriptor, beanName);
}else{
//通用处理逻辑
returndoResolveDependency(descriptor, descriptor.getDependencyType(), beanName, autowiredBeanNames, typeConverter);
}
}
protectedObjectdoResolveDependency(DependencyDescriptor descriptor, Classtype,StringbeanName, Set autowiredBeanNames, TypeConverter typeConverter) throws BeansException
{/*
* 用于支持Spring中新增的注解@Value
*/
Objectvalue = getAutowireCandidateResolver().getSuggestedValue(descriptor);
if(value !=null) {
if(valueinstanceofString) {
StringstrVal = resolveEmbeddedValue((String) value);
BeanDefinition bd = (beanName !=null&& containsBean(beanName) ? getMergedBeanDefinition(beanName) :null);
value = evaluateBeanDefinitionString(strVal, bd);
}
TypeConverter converter = (typeConverter !=null? typeConverter : getTypeConverter());
return(descriptor.getField() !=null? converter.convertIfNecessary(value,type, descriptor.getField()) : converter.convertIfNecessary(value,type, descriptor.getMethodParameter()));
}
//如果解析器没有成功解析，则需要考虑各种情况 //属性是数组类型
if(type.isArray()) {
Class componentType =type.getComponentType();
//根据属性类型找到beanFactory中所有类型的匹配bean，
//返回值的构成为：key=匹配的beanName,value=beanName对应的实例化后的bean（通过getBean(beanName)返回）
Map matchingBeans = findAutowireCandidates(beanName, componentType, descriptor);
if(matchingBeans.isEmpty()) {
//如果autowire的require属性为true而找到的匹配项却为空则只能抛出异常
if(descriptor.isRequired()) {
raiseNoSuchBeanDefinitionException(componentType,"array of "+ componentType.getName(), descriptor); }
returnnull;
}
if(autowiredBeanNames !=null) {
autowiredBeanNames.addAll(matchingBeans.keySet());
}
TypeConverter converter = (typeConverter !=null? typeConverter : getTypeConverter());
//通过转换器将bean的值转换为对应的type类型
returnconverter.convertIfNecessary(matchingBeans.values(),type);
}
//属性是Collection类型
else if(Collection.class.isAssignableFrom(type) &&type.isInterface()) {
Class elementType = descriptor.getCollectionType();
if(elementType ==null) {
if(descriptor.isRequired()) {
thrownewFatalBeanException("No element type declared for collection ["+type.getName() +"]"); }returnnull;
}
Map matchingBeans = findAutowireCandidates(beanName, elementType, descriptor);
if(matchingBeans.isEmpty()) {
if(descriptor.isRequired()) {
raiseNoSuchBeanDefinitionException(elementType,"collection of "+ elementType.getName(), descriptor);
}
returnnull;
}
if(autowiredBeanNames !=null) {
autowiredBeanNames.addAll(matchingBeans.keySet());
}
TypeConverter converter = (typeConverter !=null? typeConverter :
getTypeConverter());returnconverter.convertIfNecessary(matchingBeans.values(),type); }
//属性是Map类型
elseif(Map.class.isAssignableFrom(type) &&type.isInterface()) {
Class keyType = descriptor.getMapKeyType();if(keyType ==null|| !String.class.isAssignableFrom(keyType)) {
if(descriptor.isRequired()) {thrownewFatalBeanException("Key type ["+ keyType +"] of map ["+type.getName() +"] must be assignable to [java.lang.String]");
}
returnnull;
}
Class valueType = descriptor.getMapValueType();
if(valueType ==null) {if(descriptor.isRequired()) {
thrownewFatalBeanException("No value type declared for map ["+type.getName() +"]"); }returnnull;
}
Map matchingBeans = findAutowireCandidates(beanName, valueType, descriptor);
if(matchingBeans.isEmpty()) {
if(descriptor.isRequired()) {
raiseNoSuchBeanDefinitionException(valueType,"map with value type "+ valueType.getName(), descriptor);
}returnnull;
}
if(autowiredBeanNames !=null) {
autowiredBeanNames.addAll(matchingBeans.keySet());
}
returnmatchingBeans;
}else{
Map matchingBeans = findAutowireCandidates(beanName,type, descriptor);
if(matchingBeans.isEmpty()) {
if(descriptor.isRequired()) {
raiseNoSuchBeanDefinitionException(type,"", descriptor); }returnnull;
}
if(matchingBeans.size() >1) {StringprimaryBeanName = determinePrimaryCandidate(matchingBeans, descriptor);
if(primaryBeanName ==null) {
thrownewNoUniqueBeanDefinitionException(type, matchingBeans.keySet());
}
if(autowiredBeanNames !=null) { autowiredBeanNames.add(primaryBeanName);
}
returnmatchingBeans.get(primaryBeanName);
}
// We have exactly one match. Map.Entry entry = matchingBeans.entrySet().iterator().next();if(autowiredBeanNames !=null) { autowiredBeanNames.add(entry.getKey());
}
//已经确定只有一个匹配项 returnentry.getValue();
}
}
applyPropertyValues
程序运行到这里，已经完成了对所有注入属性的获取，但是获取的属性是以PropertyValues形式存在的，还并没有应用到已经实例化的bean中，这一工作是在applyPropertyValues中。继续跟踪到方法体中：
protectedvoidapplyPropertyValues(StringbeanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
if(pvs ==null|| pvs.isEmpty()) {
return;
}
MutablePropertyValues mpvs =null;
List original;
if(System.getSecurityManager() !=null) {
if(bwinstanceofBeanWrapperImpl) {
((BeanWrapperImpl) bw).setSecurityContext(getAccessControlContext());
}
}
if(pvsinstanceofMutablePropertyValues) {
mpvs = (MutablePropertyValues) pvs;
//如果mpvs中的值已经被转换为对应的类型那么可以直接设置到beanwapper中
if(mpvs.isConverted()) {
// Shortcut: use the pre-converted values as-is. try{
bw.setPropertyValues(mpvs);
return;
}
catch(BeansException ex) {
thrownewBeanCreationException( mbd.getResourceDescription(), beanName,"Error setting property values", ex);
}
}
original = mpvs.getPropertyValueList(); }
else{
//如果pvs并不是使用MutablePropertyValues封装的类型，那么直接使用原始的属性获取方法
original = Arrays.asList(pvs.getPropertyValues());
}
TypeConverter converter = getCustomTypeConverter();
if(converter ==null) {
converter = bw; }
//获取对应的解析器 BeanDefinitionValueResolver valueResolver =newBeanDefinitionValueResolver(this, beanName, mbd, converter);
// Create a deep copy, resolving any references for values. List deepCopy =newArrayList(original.size());booleanresolveNecessary =false;
//遍历属性，将属性转换为对应类的对应属性的类型
for(PropertyValue pv : original) {
if(pv.isConverted()) { deepCopy.add(pv);
}else{
StringpropertyName = pv.getName();
ObjectoriginalValue = pv.getValue();
ObjectresolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
ObjectconvertedValue = resolvedValue;booleanconvertible = bw.isWritableProperty(propertyName) && !PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
if(convertible) {
convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);
}
// Possibly store converted value in merged bean definition,
// in order to avoid re-conversion for every created bean instance.
if(resolvedValue == originalValue) {if(convertible) {
pv.setConvertedValue(convertedValue);
}
deepCopy.add(pv);
}
else if(convertible && originalValueinstanceofTypedStringValue && !((TypedStringValue) originalValue).isDynamic() && !(convertedValueinstanceofCollection || ObjectUtils.isArray(convertedValue))) {
pv.setConvertedValue(convertedValue);
deepCopy.add(pv);
}else{
resolveNecessary =true;
deepCopy.add(newPropertyValue(pv, convertedValue));
}
}
}
if(mpvs !=null&& !resolveNecessary) {
mpvs.setConverted();
}
// Set our (possibly massaged) deep copy. try{ bw.setPropertyValues(newMutablePropertyValues(deepCopy));
}
catch(BeansException ex) {
thrownewBeanCreationException( mbd.getResourceDescription(), beanName,"Error setting property values", ex);
}
}
我们来看看具体的属性赋值过程
publicclassMyTestBean{privateString name ;
publicMyTestBean(String name){
this.name = name; }publicMyTestBean(){ }
publicStringgetName(){
returnname;
}
publicvoidsetName(String name){
this.name = name; }
}
如上 bw.setPropertyValues 最终都会走到如下方法
@Overridepublic void setValue(final @Nullable Object value) throws Exception {
//获取writeMethod，也就是我们MyTestBean的setName方法
final Method writeMethod = (this.pdinstanceofGenericTypeAwarePropertyDescriptor ? ((GenericTypeAwarePropertyDescriptor)this.pd).getWriteMethodForActualAccess() :this.pd.getWriteMethod());
if(System.getSecurityManager() !=null) {
AccessController.doPrivileged((PrivilegedAction<Object>)()->{ ReflectionUtils.makeAccessible(writeMethod);returnnull; });
try{ AccessController.doPrivileged((PrivilegedExceptionAction<Object>)()->writeMethod.invoke(getWrappedInstance(), value), acc);
}catch(PrivilegedActionException ex) {throwex.getException(); }
}else{ ReflectionUtils.makeAccessible(writeMethod);
//通过反射调用方法进行赋值 writeMethod.invoke(getWrappedInstance(), value);
}
}
Debug如下
就是利用反射进行调用对象的set方法赋值
至此，doCreateBean() 第二个过程：属性填充 已经分析完成了，下篇分析第三个过程：循环依赖的处理，其实循环依赖并不仅仅只是在 doCreateBean() 中处理，其实在整个加载 bean 的过程中都有涉及，所以下篇内容并不仅仅只局限于 doCreateBean()。
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