7.Spring源码通俗讲解之xml中配置的bean属性是如何完成自动赋值的

准备工作

• Cat.java

package com.CodingInn.code.pojo;

import org.springframework.stereotype.Component;

@Component
public class Cat {
   private String catName = "tomcat";

   public String getCatName() {
      return catName;
   }

   public void setCatName(String catName) {
      this.catName = catName;
   }


}

• beans.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

   <bean class="com.CodingInn.code.pojo.Cat" id="cat">
      <property name="catName" value="cat"/>
   </bean>

</beans>

• 测试类

@Test
public void testXml(){
   ApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");
   Cat bean = applicationContext.getBean(Cat.class);
   System.out.println(bean.getCatName());
}

开始调试

• AnnotationConfigApplication.java

public AnnotationConfigApplicationContext(Class<?>... annotatedClasses) {
   this();
   register(annotatedClasses);
   refresh();//刷新容器
}

• AbstractApplicationContext

@Override
public void refresh() throws BeansException, IllegalStateException {
   synchronized (this.startupShutdownMonitor) {
      // Prepare this context for refreshing. 准备刷新
      prepareRefresh();

      // Tell the subclass to refresh the internal bean factory. BeanFactory第一次开始创建的时候,有xml解析逻辑
      // 创建容器对象 ,获得的是DefaultListableBeanFactory
      ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

      // Prepare the bean factory for use in this context.
      //完成beanFactory的属性设置功能
      prepareBeanFactory(beanFactory);

      try {
        ...

         // 完成BeanFactory的初始化,(工厂里面所有的组件都初始化好了)
         finishBeanFactoryInitialization(beanFactory);

         // Last step: publish corresponding event.
         finishRefresh();
      }

      catch (BeansException ex) {
       ...
      }

      finally {
       ...
      }
   }
}



protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
		...

		//  初始化所有的非懒加载的单实例Bean
		beanFactory.preInstantiateSingletons();
	}

• DefaultListableBeanFactory

@Override
public void preInstantiateSingletons() throws BeansException {
   if (logger.isDebugEnabled()) {
      logger.debug("Pre-instantiating singletons in " + this);
   }

   // Iterate over a copy to allow for init methods which in turn register new bean definitions.
   // While this may not be part of the regular factory bootstrap, it does otherwise work fine.
   List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

   // Trigger initialization of all non-lazy singleton beans...
   for (String beanName : beanNames) {
      RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);//开始解析文件的时候每一个bean标签被解析封装成一个BeanDefinition
      if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
         if (isFactoryBean(beanName)) {//如果是FactoryBean则执行以下逻辑
           ...
         }
         else {//非工厂bean
            getBean(beanName);
         }
      }
   }

• AbstractBeanFactory.java

@Override
public Object getBean(String name) throws BeansException {
   return doGetBean(name, null, null, false);
}




protected <T> T doGetBean(
			String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)
			throws BeansException {

		String beanName = transformedBeanName(name);//提取对应的beanName
		Object bean;

		// Eagerly check singleton cache for manually registered singletons.尝试从缓存获取或者singletonFactories中的ObjectFactory中获取
		检查缓存中是否存在,寻找的是DefaultSingletonBeanRegistry里的singletonObjects map是否含有对应的Object
		//    	  //DefaultListableBeanFactory是DefaultSingletonBeanRegistry的子类,DefaultSingletonBeanRegistry类中存放了很多map,用于存储bean的信息,IOC容器的单例池存放的地方
		Object sharedInstance = getSingleton(beanName);
		if (sharedInstance != null && args == null) {
			...

			...

			try {
				RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
				checkMergedBeanDefinition(mbd, beanName, args);

				// Guarantee initialization of beans that the current bean depends on.
				String[] dependsOn = mbd.getDependsOn();
				if (dependsOn != null) {
					for (String dep : dependsOn) {
						...
					}
				}

				// Create bean instance.创建bean的实例
				if (mbd.isSingleton()) {
					sharedInstance = getSingleton(beanName, () -> {
						try {
							return createBean(beanName, mbd, args); //创建bean对象的实例
						}
						catch (BeansException ex) {
							...
						}
					});
					bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
				}

				else if (mbd.isPrototype()) {
					...
				}

				else {
					...
				}
			}
			catch (BeansException ex) {
				cleanupAfterBeanCreationFailure(beanName);
				throw ex;
			}
		}

		// Check if required type matches the type of the actual bean instance.
		...
		return (T) bean;
	}

• DefaultSingletonBeanRegistry.java

public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
   Assert.notNull(beanName, "Bean name must not be null");
   synchronized (this.singletonObjects) {
      Object singletonObject = this.singletonObjects.get(beanName);
      if (singletonObject == null) {
         ...
         try {
            singletonObject = singletonFactory.getObject();ObjectFactory提供Bean实例,此处的getObect是上一步sharedInstance = getSingleton(...)的lambda表达式 createBean(beanName, mbd, args)
            newSingleton = true;
         }
         ...
      }
      return singletonObject;
   }
}

• AbstractAutowireCapableBeanFactory.java

@Override
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
      throws BeanCreationException {

   ...

   try {
      Object beanInstance = doCreateBean(beanName, mbdToUse, args);
    ...
      return beanInstance;
   }
  ...
}




protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
			throws BeanCreationException {

		// Instantiate the bean.
		BeanWrapper instanceWrapper = null;
		if (mbd.isSingleton()) {
			instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
		}
		if (instanceWrapper == null) {
           		 //创建bean实例,默认使用无参构造器
			instanceWrapper = createBeanInstance(beanName, mbd, args);
		}
		...

		...

		// Initialize the bean instance.
		Object exposedObject = bean;
		try {
			populateBean(beanName, mbd, instanceWrapper);//先给bean中的属性赋值
			exposedObject = initializeBean(beanName, exposedObject, mbd);
		}
		catch (Throwable ex) {
			...
		}

		...

		return exposedObject;
	}




protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
		...

              //从属性中拿到所有的键值对
		PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);

		...

		...

		...

		if (pvs != null) {
			applyPropertyValues(beanName, mbd, bw, pvs);//给属性赋值
		}
	}




protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
		...

		MutablePropertyValues mpvs = null;
		List<PropertyValue> original;

		if (pvs instanceof MutablePropertyValues) {
			mpvs = (MutablePropertyValues) pvs;
			if (mpvs.isConverted()) {
				// Shortcut: use the pre-converted values as-is.
				try {
					bw.setPropertyValues(mpvs);
					return;
				}
				catch (BeansException ex) {
					...
				}
			}
			original = mpvs.getPropertyValueList();
		}
		else {
			original = Arrays.asList(pvs.getPropertyValues());
		}

		TypeConverter converter = getCustomTypeConverter();
		if (converter == null) {
			converter = bw;
		}
		BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);

		// Create a deep copy, resolving any references for values.
		List<PropertyValue> deepCopy = new ArrayList<>(original.size());
		boolean resolveNecessary = false;
		for (PropertyValue pv : original) {
			if (pv.isConverted()) {
				deepCopy.add(pv);
			}
			else {
				String propertyName = pv.getName();
				Object originalValue = pv.getValue();
				Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
				Object convertedValue = resolvedValue;
				boolean convertible = bw.isWritableProperty(propertyName) &&
						!PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
				if (convertible) {
					convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);
				}
				// Possibly store converted value in merged bean definition,
				// in order to avoid re-conversion for every created bean instance.
				if (resolvedValue == originalValue) {
					if (convertible) {
						pv.setConvertedValue(convertedValue);
					}
					deepCopy.add(pv);
				}
				else if (convertible && originalValue instanceof TypedStringValue &&
						!((TypedStringValue) originalValue).isDynamic() &&
						!(convertedValue instanceof Collection || ObjectUtils.isArray(convertedValue))) {
					pv.setConvertedValue(convertedValue);
					deepCopy.add(pv);
				}
				else {
					resolveNecessary = true;
					deepCopy.add(new PropertyValue(pv, convertedValue));
				}
			}
		}
		if (mpvs != null && !resolveNecessary) {
			mpvs.setConverted();
		}

		//深拷贝所有PropertyValue对应的属性
		try {
			bw.setPropertyValues(new MutablePropertyValues(deepCopy));
		}
		catch (BeansException ex) {
			...
		}
	}

• AbstractPropertyAccessor.java

@Override
public void setPropertyValues(PropertyValues pvs) throws BeansException {
   setPropertyValues(pvs, false, false);
}



@Override
	public void setPropertyValues(PropertyValues pvs, boolean ignoreUnknown, boolean ignoreInvalid)
			throws BeansException {

		List<PropertyAccessException> propertyAccessExceptions = null;
		List<PropertyValue> propertyValues = (pvs instanceof MutablePropertyValues ?
				((MutablePropertyValues) pvs).getPropertyValueList() : Arrays.asList(pvs.getPropertyValues()));

		if (ignoreUnknown) {
			this.suppressNotWritablePropertyException = true;
		}
		try {
			for (PropertyValue pv : propertyValues) {
				// 遍历所有的属性进行赋值
				try {
					setPropertyValue(pv);
				}
				...
			}
		}
		finally {
			...
		}

		...
	}

• AbstractNestablePropertyAccessor.java

@Override
public void setPropertyValue(PropertyValue pv) throws BeansException {
   PropertyTokenHolder tokens = (PropertyTokenHolder) pv.resolvedTokens;
   if (tokens == null) {
      String propertyName = pv.getName();
      AbstractNestablePropertyAccessor nestedPa;
      try {
         nestedPa = getPropertyAccessorForPropertyPath(propertyName);
      }
      catch (NotReadablePropertyException ex) {
        ...
      }
      tokens = getPropertyNameTokens(getFinalPath(nestedPa, propertyName));
      if (nestedPa == this) {
         pv.getOriginalPropertyValue().resolvedTokens = tokens;
      }
      nestedPa.setPropertyValue(tokens, pv);
   }
   else {
      setPropertyValue(tokens, pv);
   }
}



protected void setPropertyValue(PropertyTokenHolder tokens, PropertyValue pv) throws BeansException {
		if (tokens.keys != null) {
			processKeyedProperty(tokens, pv);
		}
		else {
			processLocalProperty(tokens, pv);
		}
	}



private void processLocalProperty(PropertyTokenHolder tokens, PropertyValue pv) {
		PropertyHandler ph = getLocalPropertyHandler(tokens.actualName);//属性值处理器,通过tokens.actualName获得对应的反射函数,比如tokens.actualName是Cat类中的catName属性,ph会封装Cat类中的setCatName方法,以此来通过反射
		...

		Object oldValue = null;
		try {
			Object originalValue = pv.getValue();
			Object valueToApply = originalValue;
			if (!Boolean.FALSE.equals(pv.conversionNecessary)) {
				if (pv.isConverted()) {
					valueToApply = pv.getConvertedValue();
				}
				else {
					if (isExtractOldValueForEditor() && ph.isReadable()) {
						try {
							oldValue = ph.getValue();
						}
						catch (Exception ex) {
							...
						}
					}
					valueToApply = convertForProperty(
							tokens.canonicalName, oldValue, originalValue, ph.toTypeDescriptor());
				}
				pv.getOriginalPropertyValue().conversionNecessary = (valueToApply != originalValue);
			}
			ph.setValue(valueToApply);
		}
		...
	}

• BeanWrapperImp.java

@Override
   public void setValue(@Nullable Object value) throws Exception {
      Method writeMethod = (this.pd instanceof GenericTypeAwarePropertyDescriptor ?
            ((GenericTypeAwarePropertyDescriptor) this.pd).getWriteMethodForActualAccess() :
            this.pd.getWriteMethod());
      if (System.getSecurityManager() != null) {
         ....
      }
      else {
         ReflectionUtils.makeAccessible(writeMethod);
         writeMethod.invoke(getWrappedInstance(), value);
      }
   }
}

• Cat.java

public void setCatName(String catName) {
   this.catName = catName;
}