//根據(jù)類型對(duì)屬性進(jìn)行自動(dòng)依賴注入 protected void autowireByType(String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {//獲取用戶定義的類型轉(zhuǎn)換器TypeConverter converter = getCustomTypeConverter();if (converter == null) {converter = bw;}//存放解析的要注入的屬性Set<String> autowiredBeanNames = new LinkedHashSet<>(4);//對(duì)Bean對(duì)象中非簡(jiǎn)單屬性(不是簡(jiǎn)單繼承的對(duì)象，如8中原始類型，字符//URL等都是簡(jiǎn)單屬性)進(jìn)行處理String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);for (String propertyName : propertyNames) {try {//獲取指定屬性名稱的屬性描述器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.//不對(duì)Object類型的屬性進(jìn)行autowiring自動(dòng)依賴注入if (Object.class != pd.getPropertyType()) {//獲取屬性的setter方法MethodParameter methodParam = BeanUtils.getWriteMethodParameter(pd);// Do not allow eager init for type matching in case of a prioritized post-processor.//檢查指定類型是否可以被轉(zhuǎn)換為目標(biāo)對(duì)象的類型boolean eager = !PriorityOrdered.class.isInstance(bw.getWrappedInstance());//創(chuàng)建一個(gè)要被注入的依賴描述DependencyDescriptor desc = new AutowireByTypeDependencyDescriptor(methodParam, eager);//根據(jù)容器的Bean定義解析依賴關(guān)系，返回所有要被注入的Bean對(duì)象Object autowiredArgument = resolveDependency(desc, beanName, autowiredBeanNames, converter);if (autowiredArgument != null) {//為屬性賦值所引用的對(duì)象pvs.add(propertyName, autowiredArgument);}for (String autowiredBeanName : autowiredBeanNames) {//指定名稱屬性注冊(cè)依賴Bean名稱，進(jìn)行屬性依賴注入registerDependentBean(autowiredBeanName, beanName);if (logger.isDebugEnabled()) {logger.debug("Autowiring by type from bean name '" + beanName + "' via property '" +propertyName + "' to bean named '" + autowiredBeanName + "'");}}//釋放已自動(dòng)注入的屬性autowiredBeanNames.clear();}}catch (BeansException ex) {throw new UnsatisfiedDependencyException(mbd.getResourceDescription(), beanName, propertyName, ex);}} }

通過上面的源碼分析，我們可以看出來(lái)通過屬性名進(jìn)行自動(dòng)依賴注入的相對(duì)比通過屬性類型進(jìn)行自動(dòng)依賴注入要稍微簡(jiǎn)單一些， 但是真正實(shí)現(xiàn)屬性注入的是DefaultSingletonBeanRegistry 類的registerDependentBean()方法。

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