Spring源码分析（三）（@Autowired实现）

秒速五厘米 2022-02-09 09:47 233阅读 0赞

依赖注入的实现： [https://blog.csdn.net/qq\_37598011/article/details/84451591][https_blog.csdn.net_qq_37598011_article_details_84451591]

**在自动装配中，不需要对Bean属性做显示的依赖注入声明只需要配置autowiring属性，它具体的实现也在依赖注入中的populateBean方法中，Ioc容器会根据这个属性的配置使用反射自动查找属性的类型或者名称，然后根据属性的类型或者名称自动匹配Ioc容器中的Bean，从而完成依赖注入。**

AbstractAutowireCapableBeanFactory：

protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
    		//这里取得在BeanDefinition中设置的property值，这些property来自对BeanDefinition的解析
    		//具体的解析过程可以参看载入和解析BeanDefinitoin的分析
    		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;
    					if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
    						continueWithPropertyPopulation = false;
    						break;
    					}
    				}
    			}
    		}
    
    		if (!continueWithPropertyPopulation) {
    			return;
    		}
    		//这里对autowire注入的处理，可以根据Bean的名称或者类型来完成Bean的autowire
    		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.
    			if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
    				autowireByName(beanName, mbd, bw, newPvs);
    			}
    
    			// Add property values based on autowire by type if applicable.
    			if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
    				autowireByType(beanName, mbd, bw, newPvs);
    			}
    
    			pvs = newPvs;
    		}
    
    		boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
    		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;
    						pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
    						if (pvs == null) {
    							return;
    						}
    					}
    				}
    			}
    			if (needsDepCheck) {
    				checkDependencies(beanName, mbd, filteredPds, pvs);
    			}
    		}
    		//对属性进行注入
    		applyPropertyValues(beanName, mbd, bw, pvs);
    	}

重点是这块代码：**如果Bean配置了AUTOWIRE\_BY\_NAME、AUTOWIRE\_BY\_TYPE这两个属性则调用对应的方法。例如AUTOWIRE\_BY\_NAME它首先会根据反射机制从当前Bean中获取需要注入的属性名，然后根据这个属性名从容器中申请同名的Bean，这实际上会触发另一个Bean的生成和依赖注入的过程:**

//这里对autowire注入的处理，可以根据Bean的名称或者类型来完成Bean的autowire
    		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.
    			if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
    				autowireByName(beanName, mbd, bw, newPvs);
    			}
    
    			// Add property values based on autowire by type if applicable.
    			if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
    				autowireByType(beanName, mbd, bw, newPvs);
    			}
    
    			pvs = newPvs;
    		}

BeanName:

protected void autowireByName(
    			String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {
    
    		String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
    		for (String propertyName : propertyNames) {
    			if (containsBean(propertyName)) {
    				//使用获取的当前Bean的属性名作为Bean的名称，向Ioc容器获取Bean
    				//然后把从容器中获取的Bean设置到当前Bean的属性中
    				Object bean = getBean(propertyName);
    				pvs.add(propertyName, bean);
    				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");
    				}
    			}
    		}
    	}

[https_blog.csdn.net_qq_37598011_article_details_84451591]: https://blog.csdn.net/qq_37598011/article/details/84451591