protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
if (bw == null) {
if (mbd.hasPropertyValues()) {
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;
}
}
}
}
// 如果上面设置continueWithPropertyPopulation = false，表明用户可能已经自己填充了
// bean的属性，不需要Spring帮忙填充了。此时直接返回即可
if (!continueWithPropertyPopulation) {
return;
}
// pvs是一个MutablePropertyValues实例，里面实现了PropertyValues接口，
// 提供属性的读写操作实现，同时可以通过调用构造函数实现深拷贝
// 获取BeanDefinition里面为Bean设置上的属性值
PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);
int resolvedAutowireMode = mbd.getResolvedAutowireMode();
if (resolvedAutowireMode == AUTOWIRE_BY_NAME || resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
// Add property values based on autowire by name if applicable.
if (resolvedAutowireMode == AUTOWIRE_BY_NAME) {
autowireByName(beanName, mbd, bw, newPvs);
}
// Add property values based on autowire by type if applicable.
if (resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
autowireByType(beanName, mbd, bw, newPvs);
}
pvs = newPvs;
}
boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE);
PropertyDescriptor[] filteredPds = null;
if (hasInstAwareBpps) {
if (pvs == null) {
pvs = mbd.getPropertyValues();
}
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
// 在这里会对@Autowired标记的属性进行依赖注入
PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
return;
}
}
pvs = pvsToUse;
}
}
}
// 依赖检查，对应depend-on属性，3.0已经弃用此属性
if (needsDepCheck) {
// 过滤出所有需要进行依赖检查的属性编辑器
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
checkDependencies(beanName, mbd, filteredPds, pvs);
}
if (pvs != null) {
// 最终将属性注入到Bean的Wrapper实例里，这里的注入主要是供
// 显式配置了autowiredbyName或者ByType的属性注入，
// 针对注解来讲，由于在AutowiredAnnotationBeanPostProcessor已经完成了注入，
// 所以此处不执行
applyPropertyValues(beanName, mbd, bw, pvs);
}
}
复制代码完成了按名字或按类型自动装配后，来到脑图里第三步，对解析完但还未设置的属性进行再处理。
这里需要关注AutowiredAnnotationBeanPostProcessor实现的
postProcessProperties方法
@Override
public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) {
// 获取指定类中@Autowired相关注解的元信息
InjectionMetadata metadata = findAutowiringMetadata(beanName, bean.getClass(), pvs);
try {
// 对Bean的属性进行自动注入
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;
}
复制代码首先会去尝试获取InjectionMetadata对象，findAutowiringMetadata方法之前在分析该类的postProcessMergedBeanDefinition方法时，已经获取到了存储有该bean实例里被@Autowired或@Value标签修饰的属性列表的InjectionMetaData对象，并且将其已经放置到了缓存中。再次进入findAutowiringMetadata
在此次调用时，相关的
InjectionMetadata实例已经从缓存中获取到了，不需要再进到if里面去解析bean了，此时又回到postProcessProperties方法里，取到了InjectionMetadata实例之后直接对bean注入属性
metadata.inject(bean, beanName, pvs);
复制代码public void inject(Object target, @Nullable String beanName, @Nullable PropertyValues pvs) throws Throwable {
Collection<InjectedElement> checkedElements = this.checkedElements;
// 要注入的字段集合
Collection<InjectedElement> elementsToIterate =
(checkedElements != null ? checkedElements : this.injectedElements);
if (!elementsToIterate.isEmpty()) {
// 遍历每个字段并进行注入
for (InjectedElement element : elementsToIterate) {
if (logger.isTraceEnabled()) {
logger.trace("Processing injected element of bean '" + beanName + "': " + element);
}
element.inject(target, beanName, pvs);
}
}
}
复制代码该方法遍历每一个属性元素去调用元素的inject方法，进入inject发现又回到了AutowiredAnnotationBeanPostProcessor类里：
@Override
protected void inject(Object bean, @Nullable String beanName, @Nullable PropertyValues pvs) throws Throwable {
// 获取要注入的成员变量
Field field = (Field) this.member;
Object value;
// 如果成员变量的值先前缓存过
if (this.cached) {
// 从缓存中获取成员变量的值
value = resolvedCachedArgument(beanName, this.cachedFieldValue);
}
// 没有缓存
else {
// 创建一个成员变量的依赖描述符实例
DependencyDescriptor desc = new DependencyDescriptor(field, this.required);
desc.setContainingClass(bean.getClass());
Set<String> autowiredBeanNames = new LinkedHashSet<>(1);
Assert.state(beanFactory != null, "No BeanFactory available");
// 获取容器的类型转换器
TypeConverter typeConverter = beanFactory.getTypeConverter();
try {
// 获取注入的值
value = beanFactory.resolveDependency(desc, beanName, autowiredBeanNames, typeConverter);
}
catch (BeansException ex) {
throw new UnsatisfiedDependencyException(null, beanName, new InjectionPoint(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) &&
beanFactory.isTypeMatch(autowiredBeanName, field.getType())) {
this.cachedFieldValue = new ShortcutDependencyDescriptor(
desc, autowiredBeanName, field.getType());
}
}
}
else {
this.cachedFieldValue = null;
}
this.cached = true;
}
}
}
if (value != null) {
ReflectionUtils.makeAccessible(field);
field.set(bean, value);
}
}
}
复制代码在调用的过程中复用了其他类的装配能力，此时是给boyfriend装配上girlfriend实例，首先去缓存里看下之前是否解析过girlfriend，第一次执行会进入到else里，先用DependencyDescriptor包装一下属性field：
DependencyDescriptor desc = new DependencyDescriptor(field, this.required);
复制代码之后给desc注册上宿主的类名（Boyfriend）：
desc.setContainingClass(bean.getClass());
复制代码之后会尝试获取之前容器初始化时注册上去的转换器TypeConverter：
TypeConverter typeConverter = beanFactory.getTypeConverter();
复制代码converter用来做类型转换，默认获取spring自带的simpleTypeConverter用来处理简单类型的转换，之后执行
// 获取注入的值
value = beanFactory.resolveDependency(desc, beanName, autowiredBeanNames, typeConverter);
复制代码进入resolveDependency方法里：
@Override
@Nullable
public Object resolveDependency(DependencyDescriptor descriptor, @Nullable String requestingBeanName,
@Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) throws BeansException {
descriptor.initParameterNameDiscovery(getParameterNameDiscoverer());
if (Optional.class == descriptor.getDependencyType()) {
return createOptionalDependency(descriptor, requestingBeanName);
}
else if (ObjectFactory.class == descriptor.getDependencyType() ||
ObjectProvider.class == descriptor.getDependencyType()) {
return new DependencyObjectProvider(descriptor, requestingBeanName);
}
else if (javaxInjectProviderClass == descriptor.getDependencyType()) {
return new Jsr330Factory().createDependencyProvider(descriptor, requestingBeanName);
}
else {
Object result = getAutowireCandidateResolver().getLazyResolutionProxyIfNecessary(
descriptor, requestingBeanName);
if (result == null) {
result = doResolveDependency(descriptor, requestingBeanName, autowiredBeanNames, typeConverter);
}
return result;
}
}
复制代码在方法里会依据依赖描述符的不同类型进行不同的处理，但是最终都会到else里，真正起作用的是doResolveDependency方法
@Nullable
public Object doResolveDependency(DependencyDescriptor descriptor, @Nullable String beanName,
@Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) throws BeansException {
InjectionPoint previousInjectionPoint = ConstructorResolver.setCurrentInjectionPoint(descriptor);
try {
// 该方法最终调用了beanFactory.getBean(String, Class)，从容器中获取依赖
Object shortcut = descriptor.resolveShortcut(this);
// 如果容器缓存中存在所需依赖，这里进行短路路操作，提前结束依赖解析逻辑
if (shortcut != null) {
return shortcut;
}
Class<?> type = descriptor.getDependencyType();
// 处理@Value注解
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());
try {
return converter.convertIfNecessary(value, type, descriptor.getTypeDescriptor());
}
catch (UnsupportedOperationException ex) {
// A custom TypeConverter which does not support TypeDescriptor resolution...
return (descriptor.getField() != null ?
converter.convertIfNecessary(value, type, descriptor.getField()) :
converter.convertIfNecessary(value, type, descriptor.getMethodParameter()));
}
}
// 如果标识@Autowired注解的成员变量是复合类型，如Array，Collection，Map
// 从这个方法获取@Autowired里的值
Object multipleBeans = resolveMultipleBeans(descriptor, beanName, autowiredBeanNames, typeConverter);
if (multipleBeans != null) {
return multipleBeans;
}
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)) {
return descriptor.resolveNotUnique(descriptor.getResolvableType(), 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);
}
if (instanceCandidate instanceof Class) {
instanceCandidate = descriptor.resolveCandidate(autowiredBeanName, type, this);
}
Object result = instanceCandidate;
if (result instanceof NullBean) {
if (isRequired(descriptor)) {
raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);
}
result = null;
}
if (!ClassUtils.isAssignableValue(type, result)) {
throw new BeanNotOfRequiredTypeException(autowiredBeanName, type, instanceCandidate.getClass());
}
return result;
}
finally {
ConstructorResolver.setCurrentInjectionPoint(previousInjectionPoint);
}
}
复制代码首先尝试调用依赖描述符实例的resolveShortcut方法，尝试从容器缓存里获取属性名对应的bean实例
@Nullable
public Object resolveShortcut(BeanFactory beanFactory) throws BeansException {
return null;
}
复制代码相对于注解的这种情况，并没有实现该方法。
之后尝试从依赖描述符实例里面去获取目标实例的属性
Class<?> type = descriptor.getDependencyType();
复制代码这里的目标实例是girlfriend，之后就会调用注解候选解析器的getSuggestedValue方法尝试获取属性值，但是对于@Autowired修饰的属性来说，这一步无法获取到值
@Override
@Nullable
public Object getSuggestedValue(DependencyDescriptor descriptor) {
Object value = findValue(descriptor.getAnnotations());
if (value == null) {
MethodParameter methodParam = descriptor.getMethodParameter();
if (methodParam != null) {
value = findValue(methodParam.getMethodAnnotations());
}
}
return value;
}
复制代码该方法调用findValue方法
@Nullable
protected Object findValue(Annotation[] annotationsToSearch) {
if (annotationsToSearch.length > 0) { // qualifier annotations have to be local
AnnotationAttributes attr = AnnotatedElementUtils.getMergedAnnotationAttributes(
AnnotatedElementUtils.forAnnotations(annotationsToSearch), this.valueAnnotationType);
if (attr != null) {
return extractValue(attr);
}
}
return null;
}
复制代码该方法主要是提取@Value修饰的属性值的
回到doResolveDependency方法