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：
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createBeanInstance()实例化 beanpopulateBean()属性填充- 循环依赖的处理
initializeBean()初始化 bean
第一个过程实例化 bean在前面一篇博客中已经分析完了，这篇博客开始分析 属性填充，也就是 populateBean()
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; //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 values based on autowire by name if applicable. //根据名称自动注入 if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) { autowireByName(beanName, mbd, bw, newPvs); } // Add property values based on autowire by type if applicable. //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 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);
}
我们来分析下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
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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()
protected void 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 beanObject bean = 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：
protected String[] unsatisfiedNonSimpleProperties(AbstractBeanDefinition mbd, BeanWrapper bw) {Set<String> result = new TreeSet<>();PropertyValues pvs = mbd.getPropertyValues();PropertyDescriptor[] pds = bw.getPropertyDescriptors();for (PropertyDescriptor pd : pds) {if (pd.getWriteMethod() != null && !isExcludedFromDependencyCheck(pd) && !pvs.contains(pd.getName()) &&!BeanUtils.isSimpleProperty(pd.getPropertyType())) {result.add(pd.getName());}}return StringUtils.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：
protected void autowireByType( String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) { TypeConverter converter = getCustomTypeConverter(); if (converter == null) { converter = bw; } Set<String> autowiredBeanNames = new LinkedHashSet<String>(4); //寻找bw中需要依赖注入的属性 String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw); for (String propertyName : 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. boolean eager = !PriorityOrdered.class.isAssignableFrom(bw.getWrappedClass()); DependencyDescriptor desc = new AutowireByTypeDependencyDescriptor(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， Object autowiredArgument = resolveDependency(desc, beanName, autowiredBeanNames, converter); if (autowiredArgument != null) { pvs.add(propertyName, autowiredArgument); } for (String autowiredBeanName : 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) { throw new UnsatisfiedDependencyException(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：
@Autowired
private List<Test> 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：
public Object resolveDependency(DependencyDescriptor descriptor, String beanName, Set<String> autowiredBeanNames, TypeConverter typeConverter) throws BeansException {descriptor.initParameterNameDiscovery(getParameterNameDiscoverer()); if (descriptor.getDependencyType().equals(ObjectFactory.class)) { //ObjectFactory类注入的特殊处理 return new DependencyObjectFactory(descriptor, beanName); } else if (descriptor.getDependencyType().equals(javaxInjectProviderClass)) { //javaxInjectProviderClass类注入的特殊处理 return new DependencyProviderFactory().createDependencyProvider(descriptor, beanName); } else { //通用处理逻辑 return doResolveDependency(descriptor, descriptor.getDependencyType(), beanName, autowiredBeanNames, typeConverter); }
} protected Object doResolveDependency(DependencyDescriptor descriptor, Class<?> type, String beanName, Set<String> autowiredBeanNames, TypeConverter typeConverter) throws BeansException { /* * 用于支持Spring中新增的注解@Value */ Object value = getAutowireCandidateResolver().getSuggestedValue(descriptor); if (value != null) { if (value instanceof String) { String strVal = 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<String, Object> 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); } return null; } 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 return converter.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()) { throw new FatalBeanException("No element type declared for collection [" + type.getName() + "]"); } return null; } Map<String, Object> matchingBeans = findAutowireCandidates(beanName, elementType, descriptor); if (matchingBeans.isEmpty()) { if (descriptor.isRequired()) { raiseNoSuchBeanDefinitionException(elementType, "collection of " + elementType.getName(), descriptor); } return null; } if (autowiredBeanNames != null) { autowiredBeanNames.addAll(matchingBeans.keySet()); } TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter()); return converter.convertIfNecessary(matchingBeans.values(), type); } //属性是Map类型 else if (Map.class.isAssignableFrom(type) && type.isInterface()) { Class<?> keyType = descriptor.getMapKeyType(); if (keyType == null || !String.class.isAssignableFrom(keyType)) { if (descriptor.isRequired()) { throw new FatalBeanException("Key type [" + keyType + "] of map [" + type.getName() + "] must be assignable to [java.lang.String]"); } return null; } Class<?> valueType = descriptor.getMapValueType(); if (valueType == null) { if (descriptor.isRequired()) { throw new FatalBeanException("No value type declared for map [" + type.getName() + "]"); } return null; } Map<String, Object> matchingBeans = findAutowireCandidates(beanName, valueType, descriptor); if (matchingBeans.isEmpty()) { if (descriptor.isRequired()) { raiseNoSuchBeanDefinitionException(valueType, "map with value type " + valueType.getName(), descriptor); } return null; } if (autowiredBeanNames != null) { autowiredBeanNames.addAll(matchingBeans.keySet()); } return matchingBeans; } else { Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor); if (matchingBeans.isEmpty()) { if (descriptor.isRequired()) { raiseNoSuchBeanDefinitionException(type, "", descriptor); } return null; } if (matchingBeans.size() > 1) { String primaryBeanName = determinePrimaryCandidate(matchingBeans, descriptor); if (primaryBeanName == null) { throw new NoUniqueBeanDefinitionException(type, matchingBeans.keySet()); } if (autowiredBeanNames != null) { autowiredBeanNames.add(primaryBeanName); } return matchingBeans.get(primaryBeanName); } // We have exactly one match. Map.Entry<String, Object> entry = matchingBeans.entrySet().iterator().next(); if (autowiredBeanNames != null) { autowiredBeanNames.add(entry.getKey()); } //已经确定只有一个匹配项 return entry.getValue(); }
}
主要就是通过Type从BeanFactory中找到对应的benaName，然后通过getBean获取实例
protected Map<String, Object> findAutowireCandidates(@Nullable String beanName, Class<?> requiredType, DependencyDescriptor descriptor) {//在BeanFactory找到所有Type类型的beanNameString[] candidateNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(this, requiredType, true, descriptor.isEager());Map<String, Object> result = new LinkedHashMap<>(candidateNames.length);//遍历所有的beanName,通过getBean获取for (String candidate : candidateNames) {if (!isSelfReference(beanName, candidate) && isAutowireCandidate(candidate, descriptor)) {//addCandidateEntry(result, candidate, descriptor, requiredType);}}return result;
}private void addCandidateEntry(Map<String, Object> candidates, String candidateName,DependencyDescriptor descriptor, Class<?> requiredType) {Object beanInstance = descriptor.resolveCandidate(candidateName, requiredType, this);if (!(beanInstance instanceof NullBean)) {candidates.put(candidateName, beanInstance);}
}public Object resolveCandidate(String beanName, Class<?> requiredType, BeanFactory beanFactory)throws BeansException {//通过类型找到beanName,然后再找到其实例return beanFactory.getBean(beanName);
}
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：
protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) { if (pvs == null || pvs.isEmpty()) { return; } MutablePropertyValues mpvs = null; List<PropertyValue> original; if (System.getSecurityManager() != null) { if (bw instanceof BeanWrapperImpl) { ((BeanWrapperImpl) bw).setSecurityContext(getAccessControlContext()); } } if (pvs instanceof MutablePropertyValues) { 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) { throw new BeanCreationException( 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 = new BeanDefinitionValueResolver(this, beanName, mbd, converter); // Create a deep copy, resolving any references for values. List<PropertyValue> deepCopy = new ArrayList<PropertyValue>(original.size()); boolean resolveNecessary = 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 { String propertyName = pv.getName(); Object originalValue = pv.getValue(); Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue); Object convertedValue = resolvedValue; boolean convertible = 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 && originalValue instanceof TypedStringValue && !((TypedStringValue) originalValue).isDynamic() && !(convertedValue instanceof Collection || ObjectUtils.isArray(convertedValue))) { pv.setConvertedValue(convertedValue); deepCopy.add(pv); } else { resolveNecessary = true; deepCopy.add(new PropertyValue(pv, convertedValue)); } } } if (mpvs != null && !resolveNecessary) { mpvs.setConverted(); } // Set our (possibly massaged) deep copy. try { bw.setPropertyValues(new MutablePropertyValues(deepCopy)); } catch (BeansException ex) { throw new BeanCreationException( mbd.getResourceDescription(), beanName, "Error setting property values", ex); }
}
我们来看看具体的属性赋值过程
public class MyTestBean {private String name ;public MyTestBean(String name) {this.name = name;}public MyTestBean() {}public String getName() {return name;}public void setName(String name) {this.name = name;}
}<bean id="myTestBean" class="dabin.spring01.MyTestBean"><property name="name" value="dabin"></property>
</bean>
如上 bw.setPropertyValues 最终都会走到如下方法
@Override
public 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.pd instanceof GenericTypeAwarePropertyDescriptor ?((GenericTypeAwarePropertyDescriptor) this.pd).getWriteMethodForActualAccess() :this.pd.getWriteMethod());if (System.getSecurityManager() != null) {AccessController.doPrivileged((PrivilegedAction<Object>) () -> {ReflectionUtils.makeAccessible(writeMethod);return null;});try {AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () ->writeMethod.invoke(getWrappedInstance(), value), acc);}catch (PrivilegedActionException ex) {throw ex.getException();}}else {ReflectionUtils.makeAccessible(writeMethod);//通过反射调用方法进行赋值writeMethod.invoke(getWrappedInstance(), value);}
}
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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