java-spring 09 下.populateBean （方法成员变量的注入@Autowird，@Resource）
1.在populateBean 方法中的一部分：用于@Autowird，@Resource注入
// 后处理器已经初始化boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();// 需要依赖检查boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE);PropertyDescriptor[] filteredPds = null;if (hasInstAwareBpps) {if (pvs == null) {pvs = mbd.getPropertyValues();}// 3. 成员变量的注入// 调用了InstantiationAwareBeanPostProcessor.postProcessProperties 方法 和 postProcessPropertyValues 方法 来进行设值后处理for (BeanPostProcessor bp : getBeanPostProcessors()) {if (bp instanceof InstantiationAwareBeanPostProcessor) {InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp; // 调用设值PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);if (pvsToUse == null) {if (filteredPds == null) {filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);}// 如果postProcessProperties 返回null，再调用 postProcessPropertyValues这个过时的方法pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);if (pvsToUse == null) {return;}}pvs = pvsToUse;}}}2.关键方法ibp.postProcessProperties方法：
Spring在AutowiredAnnotationBeanPostProcessor的postProcessProperties()方法中，会遍历所找到的注入点依次进行注入。
@Overridepublic PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) {// 找注入点（所有被@Autowired注解了的Field或Method）InjectionMetadata metadata = findAutowiringMetadata(beanName, bean.getClass(), pvs);try {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;}2.1 findAutowiringMetadata方法：
属性元数据封装到AutowiredFieldElement，方法元数据封装到AutowiredMethodElement，最后都封装到InjectionMetadata
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二者都是AutowiredAnnotationBeanPostProcessor的内部类，继承InjectionMetadata.InjectedElement
metadata.inject方法：
循环遍历属性、方法元数据进行注入；封装的对象都是继承InjectedElement的
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会先进行属性注入，再进行方法注入，所以属性注入会存在被覆盖的可能
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根据这个特性，可以对static修饰的对象，进行方法注入，达到属性注入的效果
public void inject(Object target, @Nullable String beanName, @Nullable PropertyValues pvs) throws Throwable {Collection<InjectedElement> checkedElements = this.checkedElements;Collection<InjectedElement> elementsToIterate =(checkedElements != null ? checkedElements : this.injectedElements);if (!elementsToIterate.isEmpty()) {// 遍历每个注入点进行依赖注入for (InjectedElement element : elementsToIterate) {element.inject(target, beanName, pvs);}}}
element.inject方法：
这个方法会在AutowiredFieldElement和AutowiredMethodElement重写
AutowiredFieldElement.inject方法：
@Overrideprotected void inject(Object bean, @Nullable String beanName, @Nullable PropertyValues pvs) throws Throwable {Field field = (Field) this.member;Object value;if (this.cached) {// 对于原型Bean，第一次创建的时候，也找注入点，然后进行注入，此时cached为false，注入完了之后cached为true// 第二次创建的时候，先找注入点（此时会拿到缓存好的注入点），也就是AutowiredFieldElement对象，此时cache为true，也就进到此处了// 注入点内并没有缓存被注入的具体Bean对象，而是beanName，这样就能保证注入到不同的原型Bean对象try {value = resolvedCachedArgument(beanName, this.cachedFieldValue);}catch (NoSuchBeanDefinitionException ex) {// Unexpected removal of target bean for cached argument -> re-resolvevalue = resolveFieldValue(field, bean, beanName);}}else {// 根据filed从BeanFactory中查到的匹配的Bean对象value = resolveFieldValue(field, bean, beanName);}// 反射给filed赋值if (value != null) {ReflectionUtils.makeAccessible(field);field.set(bean, value);}}resolveFieldValue方法：resolveDependency方法来获取依赖的属性bean
@Nullableprivate Object resolveFieldValue(Field field, Object bean, @Nullable String beanName) {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();Object value;try {value = beanFactory.resolveDependency(desc, beanName, autowiredBeanNames, typeConverter);}catch (BeansException ex) {throw new UnsatisfiedDependencyException(null, beanName, new InjectionPoint(field), ex);}synchronized (this) {if (!this.cached) {Object cachedFieldValue = null;if (value != null || this.required) {cachedFieldValue = desc;// 注册一下beanName依赖了autowiredBeanNames，registerDependentBeans(beanName, autowiredBeanNames);if (autowiredBeanNames.size() == 1) {String autowiredBeanName = autowiredBeanNames.iterator().next();if (beanFactory.containsBean(autowiredBeanName) &&beanFactory.isTypeMatch(autowiredBeanName, field.getType())) {// 构造一个ShortcutDependencyDescriptor作为缓存，保存了当前filed所匹配的autowiredBeanName，而不是对应的bean对象（考虑原型bean）cachedFieldValue = new ShortcutDependencyDescriptor(desc, autowiredBeanName, field.getType());}}}this.cachedFieldValue = cachedFieldValue;this.cached = true;}}return value;}}
AutowiredMethodElement.inject方法：
@Overrideprotected void inject(Object bean, @Nullable String beanName, @Nullable PropertyValues pvs) throws Throwable {// 如果pvs中已经有当前注入点的值了，则跳过注入if (checkPropertySkipping(pvs)) {return;}Method method = (Method) this.member;Object[] arguments;if (this.cached) {try {arguments = resolveCachedArguments(beanName);}catch (NoSuchBeanDefinitionException ex) {// Unexpected removal of target bean for cached argument -> re-resolvearguments = resolveMethodArguments(method, bean, beanName);}}else {arguments = resolveMethodArguments(method, bean, beanName);}if (arguments != null) {try {ReflectionUtils.makeAccessible(method);method.invoke(bean, arguments);}catch (InvocationTargetException ex) {throw ex.getTargetException();}}}
resolveMethodArguments方法：
@Nullableprivate Object[] resolveMethodArguments(Method method, Object bean, @Nullable String beanName) {int argumentCount = method.getParameterCount();Object[] arguments = new Object[argumentCount];DependencyDescriptor[] descriptors = new DependencyDescriptor[argumentCount];Set<String> autowiredBeans = new LinkedHashSet<>(argumentCount);Assert.state(beanFactory != null, "No BeanFactory available");TypeConverter typeConverter = beanFactory.getTypeConverter();// 遍历每个方法参数，找到匹配的bean对象for (int i = 0; i < arguments.length; i++) {MethodParameter methodParam = new MethodParameter(method, i);DependencyDescriptor currDesc = new DependencyDescriptor(methodParam, this.required);currDesc.setContainingClass(bean.getClass());descriptors[i] = currDesc;try {Object arg = beanFactory.resolveDependency(currDesc, beanName, autowiredBeans, typeConverter);if (arg == null && !this.required) {arguments = null;break;}arguments[i] = arg;}catch (BeansException ex) {throw new UnsatisfiedDependencyException(null, beanName, new InjectionPoint(methodParam), ex);}}synchronized (this) {if (!this.cached) {if (arguments != null) {DependencyDescriptor[] cachedMethodArguments = Arrays.copyOf(descriptors, arguments.length);registerDependentBeans(beanName, autowiredBeans);if (autowiredBeans.size() == argumentCount) {Iterator<String> it = autowiredBeans.iterator();Class<?>[] paramTypes = method.getParameterTypes();for (int i = 0; i < paramTypes.length; i++) {String autowiredBeanName = it.next();if (beanFactory.containsBean(autowiredBeanName) &&beanFactory.isTypeMatch(autowiredBeanName, paramTypes[i])) {cachedMethodArguments[i] = new ShortcutDependencyDescriptor(descriptors[i], autowiredBeanName, paramTypes[i]);}}}this.cachedMethodArguments = cachedMethodArguments;}else {this.cachedMethodArguments = null;}this.cached = true;}}return arguments;}
字段注入
- 遍历所有的AutowiredFieldElement对象。
- 将对应的字段封装为DependencyDescriptor对象。
- 调用BeanFactory的resolveDependency()方法，传入DependencyDescriptor对象，进行依赖查找，找到当前字段所匹配的Bean对象。
- 将DependencyDescriptor对象和所找到的结果对象beanName封装成一个ShortcutDependencyDescriptor对象作为缓存，比如如果当前Bean是原型Bean，那么下次再来创建该Bean时，就可以直接拿缓存的结果对象beanName去BeanFactory中去那bean对象了，不用再次进行查找了
- 利用反射将结果对象赋值给字段。
Set方法注入
- 遍历所有的AutowiredMethodElement对象
- 遍历将对应的方法的参数，将每个参数封装成MethodParameter对象
- 将MethodParameter对象封装为DependencyDescriptor对象
- 调用BeanFactory的resolveDependency()方法，传入DependencyDescriptor对象，进行依赖查找，找到当前方法参数所匹配的Bean对象。
- 将DependencyDescriptor对象和所找到的结果对象beanName封装成一个ShortcutDependencyDescriptor对象作为缓存，比如如果当前Bean是原型Bean，那么下次再来创建该Bean时，就可以直接拿缓存的结果对象beanName去BeanFactory中去那bean对象了，不用再次进行查找了
- 利用反射将找到的所有结果对象传给当前方法，并执行。