PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
if (hasInstAwareBpps) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvs == null) {
return;
}
}
}
}
spring中默认注册了以下几种beanPostProcessor,如下：
每一个beanPostProcessor都会在实例化前后相应的地方进行调用。在这里我们需要关注的是```AutowiredAnnotationBeanPostProcessor```,```RequiredAnnotationBeanPostProcessor```,```CommonAnnotationBeanPostProcessor```这几个注解。
顾名思义这几个beanPostProcessor都是用来处理注解的，对应用来处理```@Autowired```,```@Required```,```@Common```几个注解。
这里以```@Autowored```的处理为例。
#### AutowiredAnnotationBeanPostProcessor
public PropertyValues postProcessPropertyValues(
PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException {
InjectionMetadata metadata = findAutowiringMetadata(beanName, bean.getClass());
try {
metadata.inject(bean, beanName, pvs);
}catch (Throwable ex) {
throw new BeanCreationException(beanName, "Injection of autowired dependencies failed", ex);
}
return pvs;
}
private InjectionMetadata buildAutowiringMetadata(Class<?> clazz) {
LinkedList<InjectionMetadata.InjectedElement> elements = new LinkedList<InjectionMetadata.InjectedElement>();
Class<?> targetClass = clazz;
do {
LinkedList<InjectionMetadata.InjectedElement> currElements = new LinkedList<InjectionMetadata.InjectedElement>();
for (Field field : targetClass.getDeclaredFields()) {
AnnotationAttributes annotation = findAutowiredAnnotation(field);
if (annotation != null) {
if (Modifier.isStatic(field.getModifiers())) {
if (logger.isWarnEnabled()) {
logger.warn("Autowired annotation is not supported on static fields: " + field);
}
continue;
}
boolean required = determineRequiredStatus(annotation);
currElements.add(new AutowiredFieldElement(field, required));
}
}
for (Method method : targetClass.getDeclaredMethods()) {
Method bridgedMethod = BridgeMethodResolver.findBridgedMethod(method);
if (!BridgeMethodResolver.isVisibilityBridgeMethodPair(method, bridgedMethod)) {
continue;
}
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);
}
continue;
}
if (method.getParameterTypes().length == 0) {
if (logger.isWarnEnabled()) {
logger.warn("Autowired annotation should be used on methods with actual 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);
}
该方法主要就是通过解析当前bean有哪些属性被```@Autowired```注解修饰，将其封装为一个```InjectionMetadata```对象。解析的过程通过```findAutowiringMetadata(String beanName, Class<?> clazz)```完成，但实际上主要还是通过上面的```buildAutowiringMetadata(Class<?> clazz)```完成。
方法比较简单，首先就是遍历bean的所有字段(Field),通过反射的方法查找字段上的注解，如果存在匹配的注解(```AutowiredAnnotationBeanPostProcessor```匹配的就是```@Autowired```)。如果存在该注解就将这个字段记录表示需要进行注入。
当将字段遍历完成后就取出所有的方法，查找方法上是否有该注解，如果存在的话同理记录下该方法。
对于被记录下的字段或者方法会被封装成一个```InjectedElement```对象。通过该对象的inject方法完成注入工作。
