SpringMVC 源代码深度解析 IOC容器（Bean实例化和依赖注入）

清疚 2022-08-13 14:40 181阅读 0赞

SpringMVC最核心的IOC的控制反转，动态的向某个对象提供它所需要的其他对象，例如：对象A时，需要对象B时，这时不像以前我们之前要在A对象里实例化B对象，这时B对象的实例化由IOC容器会主动创建一个对象B然后注入到对象A里，提供使用。我们项目开发中，最经常用到，那怎么实现实例Bean并依赖注入呢？我们今天带着这些问题来通过SpringMVC源代码进行深入的解析。这篇介绍不对注解实例化和注入进行讲解，这个放在后面在介绍。

我们平常写的一个类，并依赖调用了类的某个方法，这时需要依赖那个类已经实例化，这样才能调用，这些都是交给IOC控制反转，这是我们写的一个类，代码如下

package cn.test.service.impl;
    
    import cn.test.service.TestService2;
    
    public class TestServiceImpl2 implements TestService2{
    
    }

package cn.test.service.impl;
    
    import cn.test.service.TestService;
    import cn.test.service.TestService2;
    
    public class TestServiceImpl implements TestService{
    	
    	
    	private TestServiceImpl(){
    		System.out.println("xx");
    	}
    
    	private TestService2 testService2;
    
    	public TestService2 getTestService2() {
    		return testService2;
    	}
    
    	public void setTestService2(TestService2 testService2) {
    		this.testService2 = testService2;
    	}
    	
    }

在配置文件配置了对应的Bean

那SpringMVC  怎么实现实例 B ean并依赖注入？我们带着上面实现的代码来解析。

首先我们先回到refresh这个方法，在[上一篇Bean解析和注册][Bean]，大家应该还记得吧，里面有postProcessBeanFactory这个方法，就是实例化bean的，我们带着好奇心来分析了解。当Bean定义资源被载入IoC容器之后，容器将Bean定义资源解析为容器内部的数据结构，然后BeanDefinition注册到容器中，AbstractApplicationContext类中的finishBeanFactoryInitialization方法对配置了属性的Bean进行初始化过程，源码如下：

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
 		// CONVERSION_SERVICE_BEAN_NAME为转换服务(ConversionService)  
 		if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
 				beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
 			beanFactory.setConversionService(
 					beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
 		}
 
 		// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
 		String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
 		for (String weaverAwareName : weaverAwareNames) {
 			getBean(weaverAwareName);
 		}
 
 		// Stop using the temporary ClassLoader for type matching.
 		beanFactory.setTempClassLoader(null);
 
 		// Allow for caching all bean definition metadata, not expecting further changes.
 		beanFactory.freezeConfiguration();
 
 		// 对bean进行实例化
 		beanFactory.preInstantiateSingletons();
 	}

preInstantiateSingletons由对bean进行实例化由子类DefaultListableBeanFactory来实现的。源代码：

public void preInstantiateSingletons() throws BeansException {
 		if (this.logger.isInfoEnabled()) {
 			this.logger.info("Pre-instantiating singletons in " + this);
 		}
 		List<String> beanNames;
 		synchronized (this.beanDefinitionMap) {
 			// 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.
 			beanNames = new ArrayList<String>(this.beanDefinitionNames);
 		}
 		for (String beanName : beanNames) {
 			RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
 			if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
 				if (isFactoryBean(beanName)) {
 					final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
 					boolean isEagerInit;
 					if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
 						isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
 							public Boolean run() {
 								return ((SmartFactoryBean<?>) factory).isEagerInit();
 							}
 						}, getAccessControlContext());
 					}
 					else {
 						isEagerInit = (factory instanceof SmartFactoryBean &&
 								((SmartFactoryBean<?>) factory).isEagerInit());
 					}
 					if (isEagerInit) {
 						getBean(beanName);
 					}
 				}
 				else {
 					getBean(beanName);
 				}
 			}
 		}
 	}

getBean(beanName);对bean进行实例化并对属性依赖进行注入过程。前面解析的代码不重要，主要是入口点，接下来才是重点， 创建bean时，如果缓存中有单例Bean时，就从缓存获取，如果没有就新建，通过匿名的内部类来创建Bean时根据Bean的作用域来创建的，有单实例作用域、原型作用域、Request等。源代码如下：

public Object getBean(String name) throws BeansException {
 		return doGetBean(name, null, null, false);
 	}
 	@SuppressWarnings("unchecked")
 	protected <T> T doGetBean(
 			final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
 			throws BeansException {
 //如果指定的是别名，将别名转换为规范的Bean名称 
 		final String beanName = transformedBeanName(name);
 		Object bean;
 
 		// 如果缓存中有单例Bean时，就从缓存获取
 		Object sharedInstance = getSingleton(beanName);
 		if (sharedInstance != null && args == null) {
 			if (logger.isDebugEnabled()) {
 				if (isSingletonCurrentlyInCreation(beanName)) {
 					logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
 							"' that is not fully initialized yet - a consequence of a circular reference");
 				}
 				else {
 					logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
 				}
 			}
 			bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
 		}
 
 		else {
 			// Fail if we're already creating this bean instance:
 			// We're assumably within a circular reference.
 			if (isPrototypeCurrentlyInCreation(beanName)) {
 				throw new BeanCurrentlyInCreationException(beanName);
 			}
 
 			// 获取父工厂
 			BeanFactory parentBeanFactory = getParentBeanFactory();
 //检查BeanDefinition是否有当前的BeanFactory，如果没有，就到父工厂去查找
 			if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
 				// Not found -> check parent.
 				String nameToLookup = originalBeanName(name);
 				if (args != null) {
 					// Delegation to parent with explicit args.
 					return (T) parentBeanFactory.getBean(nameToLookup, args);
 				}
 				else {
 					// No args -> delegate to standard getBean method.
 					return parentBeanFactory.getBean(nameToLookup, requiredType);
 				}
 			}
 
 			if (!typeCheckOnly) {
 				markBeanAsCreated(beanName);
 			}
 
 			try {
 //看说明（2）
 				final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
 
 //是否为抽象的、是否Prototype
 				checkMergedBeanDefinition(mbd, beanName, args);
 
 				// 获取当前Bean所有依赖Bean的名称
 				String[] dependsOn = mbd.getDependsOn();
 				if (dependsOn != null) {
 					for (String dependsOnBean : dependsOn) {
 //递归调用getBean方法
 						getBean(dependsOnBean);
 //注册依赖的bean
 						registerDependentBean(dependsOnBean, beanName);
 					}
 				}
 
 				// 创建单例bean实例
 				if (mbd.isSingleton()) {
 //内部类，实现创建bean
 					sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
 						public Object getObject() throws BeansException {
 							try {
 //创建bean
 								return createBean(beanName, mbd, args);
 							}
 							catch (BeansException ex) {
 								// Explicitly remove instance from singleton cache: It might have been put there
 								// eagerly by the creation process, to allow for circular reference resolution.
 								// Also remove any beans that received a temporary reference to the bean.
 								destroySingleton(beanName);
 								throw ex;
 							}
 						}
 					});
 //获取bean实例对象
 					bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
 				}
 //是否为原型bean 每次我们从容器中调用bean时，都返回一个新的实例
 				else if (mbd.isPrototype()) {
 					// 原型bean都会创建一个新的出来
 					Object prototypeInstance = null;
 					try {
 //注册新bean
 						beforePrototypeCreation(beanName);
 //创建新的bean实例对象
 						prototypeInstance = createBean(beanName, mbd, args);
 					}
 					finally {
 						afterPrototypeCreation(beanName);
 					}
 //获取bean对象
 					bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
 				}
 
 				else {
 //创建Bean作用域类型 request、session、globalSession,通过Scope接口定义新的作用域
 					String scopeName = mbd.getScope();
 					final Scope scope = this.scopes.get(scopeName);
 					if (scope == null) {
 						throw new IllegalStateException("No Scope registered for scope '" + scopeName + "'");
 					}
 					try {
 						Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
 							public Object getObject() throws BeansException {
 								beforePrototypeCreation(beanName);
 								try {
 									return createBean(beanName, mbd, args);
 								}
 								finally {
 									afterPrototypeCreation(beanName);
 								}
 							}
 						});
 						bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
 					}
 					catch (IllegalStateException ex) {
 						throw new BeanCreationException(beanName,
 								"Scope '" + scopeName + "' is not active for the current thread; " +
 								"consider defining a scoped proxy for this bean if you intend to refer to it from a singleton",
 								ex);
 					}
 				}
 			}
 			catch (BeansException ex) {
 				cleanupAfterBeanCreationFailure(beanName);
 				throw ex;
 			}
 		}
 
 		// Check if required type matches the type of the actual bean instance.
 		if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
 			try {
 				return getTypeConverter().convertIfNecessary(bean, requiredType);
 			}
 			catch (TypeMismatchException ex) {
 				if (logger.isDebugEnabled()) {
 					logger.debug("Failed to convert bean '" + name + "' to required type [" +
 							ClassUtils.getQualifiedName(requiredType) + "]", ex);
 				}
 				throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
 			}
 		}
 		return (T) bean;
 	}

我们解析到这边，对前面的思路在整理一下，这样我们到后面就比较不会那么模糊

总结：（1）先List<String> beanDefinitionNames获取BeanName，然后通过BeanName 获取Map<String, RootBeanDefinition> RootBeanDefinition，然后判断是否              为单例、不是抽象、是为Lazy-init=false 然后调用getBean方法。我们在配置中可以定义父Bean和子bean，父Bean用RootBeanDefinition 表示，子Bean                            用ChildBeanDefinition表示，而没有父Bean用RootBeanDefinition 表示。如图所示：

![Center][]

（2）如果BeanName是别名，先转换为原来的BeanName不是别名，然后如果缓存中有单例Bean时，就从缓存获取，如果没有的话，就创建一个

（3）先检查是否父工厂存在，如果有的话，获取父工厂

（4）判断Bean依赖对象所有的名称，如果有的话，获取依赖对象的名称，然后循环getBean（）；

（5）检查Bean的作用域，Scope  作用域、原型作用域、Request等，来实例化Bean ,是由FactoryBean是创建创建对象的工厂Bean，通过调用这个对象                        的 getObject 方法就能获取用户自定义产生的对象，从而为 Spring 提供了很好的扩展性。Spring 获取 FactoryBean 本身的对象是在前面加上 & 来完成                  的。

现在思路就比较清晰了，接下来我们来解析具体实现创建Bean实例化的类。

接下来我们来继续分析具体的创建过程createBean(beanName, mbd, args);这个方法，是由AbstractAutowireCapableBeanFactory来实现的，AbstractAutowireCapableBeanFactory我们来看看它的继承关系，之前就有总体的继承关系，我们这边在温习一下，如图所示：

![Center 1][]

createBean(beanName, mbd, args);这个方法，源代码如下：

@Override
 	protected Object createBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
 			throws BeanCreationException {
 
 		if (logger.isDebugEnabled()) {
 			logger.debug("Creating instance of bean '" + beanName + "'");
 		}
 		// Make sure bean class is actually resolved at this point.
 		resolveBeanClass(mbd, beanName);
 
 		// Prepare method overrides.
 		try {
 			mbd.prepareMethodOverrides();
 		}
 		catch (BeanDefinitionValidationException ex) {
 			throw new BeanDefinitionStoreException(mbd.getResourceDescription(),
 					beanName, "Validation of method overrides failed", ex);
 		}
 
 		try {
 			// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
 			Object bean = resolveBeforeInstantiation(beanName, mbd);
 			if (bean != null) {
 				return bean;
 			}
 		}
 		catch (Throwable ex) {
 			throw new BeanCreationException(mbd.getResourceDescription(), beanName,
 					"BeanPostProcessor before instantiation of bean failed", ex);
 		}
 
 		Object beanInstance = doCreateBean(beanName, mbd, args);
 		if (logger.isDebugEnabled()) {
 			logger.debug("Finished creating instance of bean '" + beanName + "'");
 		}
 		return beanInstance;
 	}

我们这里来看最主要的创建bean实例对象的方法doCreateBean();

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {
 		// 封装bean对象
 		BeanWrapper instanceWrapper = null;
 //是否为单实例
 		if (mbd.isSingleton()) {
 //根据beanName从容器中获取
 			instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
 		}
 		if (instanceWrapper == null) {
 //创建
 			instanceWrapper = createBeanInstance(beanName, mbd, args);
 		}
 //获取bean的实例化
 		final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
 //bean的类型
 		Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
 
 		// Allow post-processors to modify the merged bean definition.
 		synchronized (mbd.postProcessingLock) {
 			if (!mbd.postProcessed) {
 				applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
 				mbd.postProcessed = true;
 			}
 		}
 
 		
 		boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
 				isSingletonCurrentlyInCreation(beanName));
 		if (earlySingletonExposure) {
 			if (logger.isDebugEnabled()) {
 				logger.debug("Eagerly caching bean '" + beanName +
 						"' to allow for resolving potential circular references");
 			}
 //向容器中缓存单态实例的Bean对象，以防循环实例化 
 			addSingletonFactory(beanName, new ObjectFactory<Object>() {
 				public Object getObject() throws BeansException {
 					return getEarlyBeanReference(beanName, mbd, bean);
 				}
 			});
 		}
 
 		// Initialize the bean instance.
 		Object exposedObject = bean;
 		try {
 //设置bean实例的属性,如果属性需要注入的bean实例，则把bean实例对象封装好依赖注入
 			populateBean(beanName, mbd, instanceWrapper);
 			if (exposedObject != null) {
 //初始化bean
 				exposedObject = initializeBean(beanName, exposedObject, mbd);
 			}
 		}
 		catch (Throwable ex) {
 			if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
 				throw (BeanCreationException) ex;
 			}
 			else {
 				throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
 			}
 		}
 
 		if (earlySingletonExposure) {
 //获取实例化好的单态实例的bean
 			Object earlySingletonReference = getSingleton(beanName, false);
 			if (earlySingletonReference != null) {
 				if (exposedObject == bean) {
 					exposedObject = earlySingletonReference;
 				}
 				else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
 					String[] dependentBeans = getDependentBeans(beanName);
 					Set<String> actualDependentBeans = new LinkedHashSet<String>(dependentBeans.length);
 					for (String dependentBean : dependentBeans) {
 						if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
 							actualDependentBeans.add(dependentBean);
 						}
 					}
 					if (!actualDependentBeans.isEmpty()) {
 						throw new BeanCurrentlyInCreationException(beanName,
 								"Bean with name '" + beanName + "' has been injected into other beans [" +
 								StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
 								"] in its raw version as part of a circular reference, but has eventually been " +
 								"wrapped. This means that said other beans do not use the final version of the " +
 								"bean. This is often the result of over-eager type matching - consider using " +
 								"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
 					}
 				}
 			}
 		}
 
 		// Register bean as disposable.
 		try {
 			registerDisposableBeanIfNecessary(beanName, bean, mbd);
 		}
 		catch (BeanDefinitionValidationException ex) {
 			throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
 		}
 
 		return exposedObject;
 	}

我们对这个方法在总结一下：

（1）封装Bean，用 BeanWrapper是对Bean的包装，其接口中所定义的功能很简单包括设置获取被包装的对象，获取被包装bean的属性描述器，由于BeanWrapper接口是PropertyAccessor的子接口，因此其也可以设置以及访问被包装对象的属性值。BeanWrapper大部分情况下是在IOC内部进行使用，通过BeanWrapper,IOC容器可以用统一的方式来访问Bean的属性。[上一篇转载的有介绍BeanWrapper][BeanWrapper],这里就不具体介绍了。

（2）根据BeanName去容器缓存中获取已经Bean的包装好的BeanWrapper，如果没有就调用createBeanInstance(beanName, mbd, args)，实例化Bean

（3）获取Bean的类型，这个类型是什么，如图所示：

![Center 2][]

(4)获取BeanWrapper里已经实例好的Bean，然后放到缓存，这样下次已经有了，就不用在创建。

（5）设置Bean实例的属性,对需要转换的属性进行转换，例如数组等，如果属性是引用类型，如果引用Bean没实例化，要在实例化，把bean实例对象封装好依赖注入在注入进来。

这里面有两个重要的实现方法createBeanInstance(beanName, mbd, args);和populateBean(beanName, mbd, instanceWrapper);createBeanInstance是创建bean实例的，populateBean设置属性的，如果属性的是对象，需要把依赖的对象创建好，设置实例化对象。这两个方法也是重点。

第一个：我们来分析createBeanInstance的方法,这里有介绍了注解的实例化，我们后面章节在介绍。可以带有参数构造函数或者默认无参的构造函数、还有工厂方法来创建Bean的实例，源代码如下：

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, Object[] args) {
 		// 确实bean是否能实例化
 		Class<?> beanClass = resolveBeanClass(mbd, beanName);
 
 		if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {
 			throw new BeanCreationException(mbd.getResourceDescription(), beanName,
 					"Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
 		}
 
 		if (mbd.getFactoryMethodName() != null) {
 // //使用工厂方法实例化bean
 			return instantiateUsingFactoryMethod(beanName, mbd, args);
 		}
 
 		// Shortcut when re-creating the same bean...
 		boolean resolved = false;
 		boolean autowireNecessary = false;
 		if (args == null) {
 			synchronized (mbd.constructorArgumentLock) {
 				if (mbd.resolvedConstructorOrFactoryMethod != null) {
 					resolved = true;
 					autowireNecessary = mbd.constructorArgumentsResolved;
 				}
 			}
 		}
 		if (resolved) {
 			if (autowireNecessary) {
 				return autowireConstructor(beanName, mbd, null, null);
 			}
 			else {
 //实例化bean
 				return instantiateBean(beanName, mbd);
 			}
 		}
 
 		// Need to determine the constructor...
 、、
 		Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
 		if (ctors != null ||
 				mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR ||
 				mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
 			return autowireConstructor(beanName, mbd, ctors, args);
 		}
 
 		// No special handling: simply use no-arg constructor.
 		return instantiateBean(beanName, mbd);
 	}

instantiateBean默认是实例化无参的构造函数的。

protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {
 		try {
 			Object beanInstance;
 			final BeanFactory parent = this;
 			if (System.getSecurityManager() != null) {
 				beanInstance = AccessController.doPrivileged(new PrivilegedAction<Object>() {
 					public Object run() {
 						return getInstantiationStrategy().instantiate(mbd, beanName, parent);
 					}
 				}, getAccessControlContext());
 			}
 			else {
 				beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);
 			}
 			BeanWrapper bw = new BeanWrapperImpl(beanInstance);
 			initBeanWrapper(bw);
 			return bw;
 		}
 		catch (Throwable ex) {
 			throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex);
 		}
 	}

getInstantiationStrategy().instantiate(mbd, beanName, parent);是由InstantiationStrategy的子类SimpleInstantiationStrategy来实现的，关系如图所示：

![Center 3][]

为了方便我们采用不同的实例化策略，以满足不同应用的需求，可以用CGLib类库来动态的创建Bean实例或者JDK反射机制来实现的，在子类中生成方法注入的逻辑，然后使用这个动态生成的子类创建bean的实例，这个实例化过程是没有对bean进行设置属性的，是有BeanWrapper 来设置的。具体由instantiate实现的，这里面说明了，如果方法有被覆盖，用JDK反射机制来实例化，否则用CGLib类库来动态的创建Bean实例，这里用beanDefinition.resolvedConstructorOrFactoryMethod来判断的。源代码如下：

public Object instantiate(RootBeanDefinition beanDefinition, String beanName, BeanFactory owner) {
 		// Don't override the class with CGLIB if no overrides.
 		if (beanDefinition.getMethodOverrides().isEmpty()) {
 			Constructor<?> constructorToUse;
 			synchronized (beanDefinition.constructorArgumentLock) {
 				constructorToUse = (Constructor<?>) beanDefinition.resolvedConstructorOrFactoryMethod;
 				if (constructorToUse == null) {
 					final Class<?> clazz = beanDefinition.getBeanClass();
 					if (clazz.isInterface()) {
 						throw new BeanInstantiationException(clazz, "Specified class is an interface");
 					}
 					try {
 //用java反射机制来实例化bean
 						if (System.getSecurityManager() != null) {
 							constructorToUse = AccessController.doPrivileged(new PrivilegedExceptionAction<Constructor>() {
 								public Constructor<?> run() throws Exception {
 									return clazz.getDeclaredConstructor((Class[]) null);
 								}
 							});
 						}
 						else {
 							constructorToUse =	clazz.getDeclaredConstructor((Class[]) null);
 						}
 						beanDefinition.resolvedConstructorOrFactoryMethod = constructorToUse;
 					}
 					catch (Exception ex) {
 						throw new BeanInstantiationException(clazz, "No default constructor found", ex);
 					}
 				}
 			}
 			return BeanUtils.instantiateClass(constructorToUse);
 		}
 		else {
 			// Must generate CGLIB subclass.
 //用CGLIB 来动态创建bean
 			return instantiateWithMethodInjection(beanDefinition, beanName, owner);
 		}
 	}

SimpleInstantiationStrategy，如果方法有被覆盖，用JDK反射机制来实例化，否则用CGLib类库来动态的创建Bean实例。这里CGLib类继承，如图所示：

![Center 4][]

这里我们来验证一下如果方法有被覆盖，用JDK反射机制来实例化，否则用CGLib类库来动态的创建Bean实例，还记得我们最开始的TestServiceImpl这个类，并在配置文件配置了Bean，在实例化肯定是使用了，JDK反射机制来实例化，因为它类还有依赖了TestServiceImpl2这个类，我们跟踪代码证实一下：

![Center 5][]

我们这边有写了一个无参的构造函数，并且有实例化，然后我们继续跟踪是采用什么实例化，如图所示：

![Center 6][]

![Center 7][]

经过我们验证是正确的。

第二个：实例化就讲到这里，接下去我们继续解析Bean属性的注入。

实现的方法是populateBean这个方法，应该还记得吧。doCreateBean();方法里面的。

protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
 		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;
 		}
 
 		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;
 ///使用BeanPostProcessor处理器处理属性值 
 						pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
 						if (pvs == null) {
 							return;
 						}
 					}
 				}
 			}
 			if (needsDepCheck) {
 				checkDependencies(beanName, mbd, filteredPds, pvs);
 			}
 		}
 //对属性的注入
 		applyPropertyValues(beanName, mbd, bw, pvs);
 	}

先获取 PropertyValues 就是获取Bean配置里面属性的值，然后调用 applyPropertyValues这个方法，applyPropertyValues方法的源代码如下：

protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
 		if (pvs == null || pvs.isEmpty()) {
 			return;
 		}
 
 		MutablePropertyValues mpvs = null;
 		List<PropertyValue> original;
 
 		if (System.getSecurityManager() != null) {
 			if (bw instanceof BeanWrapperImpl) {
 				((BeanWrapperImpl) bw).setSecurityContext(getAccessControlContext());
 			}
 		}
 //对属性进行循环
 		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) {
 					throw new BeanCreationException(
 							mbd.getResourceDescription(), beanName, "Error setting property values", ex);
 				}
 			}
 			original = mpvs.getPropertyValueList();
 		}
 		else {
 //获取了<property name="testService2" ref="testService2"></property>里面的ref值或者value
 			original = Arrays.asList(pvs.getPropertyValues());
 		}
 //获取用户自定义的类型转换
 		TypeConverter converter = getCustomTypeConverter();
 		if (converter == null) {
 			converter = bw;
 		}
 //实现了一个BeanDefinition的解析实例
 		BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);
 
 		//对属性值进行复制 
 		List<PropertyValue> deepCopy = new ArrayList<PropertyValue>(original.size());
 		boolean resolveNecessary = false;
 		for (PropertyValue pv : original) {
 //是否要转换
 			if (pv.isConverted()) {
 				deepCopy.add(pv);
 			}
 			else {
 //获取名称
 				String propertyName = pv.getName();
 //获取值
 				Object originalValue = pv.getValue();
 //对属性对应的值进行转换对应的类型
 				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();
 		}
 
 		// Set our (possibly massaged) deep copy.
 		try {
 			bw.setPropertyValues(new MutablePropertyValues(deepCopy));
 		}
 		catch (BeansException ex) {
 			throw new BeanCreationException(
 					mbd.getResourceDescription(), beanName, "Error setting property values", ex);
 		}
 	}

总结：

（1）对属性进行循环，然后获取属性值

（2）获取用户自定义的类型转换

（3）实现了一个BeanDefinition的解析实例的BeanDefinitionValueResolver，我们来看一个这个类的属性，有保存用户自定义的转换类型、还有保存BeanDefinition

![Center 8][]

（4）对属性值进行复制，如图所示：

![Center 9][]

（5）在（3）实例化了一个BeanDefinition解析实例的BeanDefinitionValueResolver对象，通过这个对象调用对具体实现了解析属性值进行解析，并对属性值进行转换。转换类型有对象引用、对集合数组类型的属性解析等。如果对引用对象进行解析时，调用了getBean（）方法。

接下来我们来解析属性的具体解析，是由BeanDefinitionValueResolver类实现的,具体实现了解析属性值进行解析，并对属性值进行转换。

resolveValueIfNecessary方法源代码如下：

ublic Object resolveValueIfNecessary(Object argName, Object value) {
 		// 对引用的类型进行转换
 		// to another bean to be resolved.
 		if (value instanceof RuntimeBeanReference) {
 			RuntimeBeanReference ref = (RuntimeBeanReference) value;
 			return resolveReference(argName, ref);
 		}
 		else if (value instanceof RuntimeBeanNameReference) {
 			String refName = ((RuntimeBeanNameReference) value).getBeanName();
 			refName = String.valueOf(evaluate(refName));
 			if (!this.beanFactory.containsBean(refName)) {
 				throw new BeanDefinitionStoreException(
 						"Invalid bean name '" + refName + "' in bean reference for " + argName);
 			}
 			return refName;
 		}
 		else if (value instanceof BeanDefinitionHolder) {
 			// Resolve BeanDefinitionHolder: contains BeanDefinition with name and aliases.
 			BeanDefinitionHolder bdHolder = (BeanDefinitionHolder) value;
 			return resolveInnerBean(argName, bdHolder.getBeanName(), bdHolder.getBeanDefinition());
 		}
 		else if (value instanceof BeanDefinition) {
 			// Resolve plain BeanDefinition, without contained name: use dummy name.
 			BeanDefinition bd = (BeanDefinition) value;
 			return resolveInnerBean(argName, "(inner bean)", bd);
 		}
 //对集合数组类型的属性解析 
 		else if (value instanceof ManagedArray) {
 			// May need to resolve contained runtime references.
 			ManagedArray array = (ManagedArray) value;
 			Class<?> elementType = array.resolvedElementType;
 			if (elementType == null) {
 				String elementTypeName = array.getElementTypeName();
 				if (StringUtils.hasText(elementTypeName)) {
 					try {
 						elementType = ClassUtils.forName(elementTypeName, this.beanFactory.getBeanClassLoader());
 						array.resolvedElementType = elementType;
 					}
 					catch (Throwable ex) {
 						// Improve the message by showing the context.
 						throw new BeanCreationException(
 								this.beanDefinition.getResourceDescription(), this.beanName,
 								"Error resolving array type for " + argName, ex);
 					}
 				}
 				else {
 					elementType = Object.class;
 				}
 			}
 			return resolveManagedArray(argName, (List<?>) value, elementType);
 		}
 		else if (value instanceof ManagedList) {
 			// May need to resolve contained runtime references.
 			return resolveManagedList(argName, (List<?>) value);
 		}
 		else if (value instanceof ManagedSet) {
 			// May need to resolve contained runtime references.
 			return resolveManagedSet(argName, (Set<?>) value);
 		}
 		else if (value instanceof ManagedMap) {
 			// May need to resolve contained runtime references.
 			return resolveManagedMap(argName, (Map<?, ?>) value);
 		}
 		else if (value instanceof ManagedProperties) {
 			Properties original = (Properties) value;
 			Properties copy = new Properties();
 			for (Map.Entry propEntry : original.entrySet()) {
 				Object propKey = propEntry.getKey();
 				Object propValue = propEntry.getValue();
 				if (propKey instanceof TypedStringValue) {
 					propKey = evaluate((TypedStringValue) propKey);
 				}
 				if (propValue instanceof TypedStringValue) {
 					propValue = evaluate((TypedStringValue) propValue);
 				}
 				copy.put(propKey, propValue);
 			}
 			return copy;
 		}
 		else if (value instanceof TypedStringValue) {
 			// Convert value to target type here.
 			TypedStringValue typedStringValue = (TypedStringValue) value;
 			Object valueObject = evaluate(typedStringValue);
 			try {
 				Class<?> resolvedTargetType = resolveTargetType(typedStringValue);
 				if (resolvedTargetType != null) {
 					return this.typeConverter.convertIfNecessary(valueObject, resolvedTargetType);
 				}
 				else {
 					return valueObject;
 				}
 			}
 			catch (Throwable ex) {
 				// Improve the message by showing the context.
 				throw new BeanCreationException(
 						this.beanDefinition.getResourceDescription(), this.beanName,
 						"Error converting typed String value for " + argName, ex);
 			}
 		}
 		else {
 			return evaluate(value);
 		}
 	}

这里我们来验证一下我们解析是否正确，还记得我们最开始的TestServiceImpl这个类，并在配置文件配置了Bean，它类还有依赖了TestServiceImpl2这个类，在配置文件

<bean id="testService" class="cn.test.service.impl.TestServiceImpl" > <property name="testService2" ref="testService2"></property></bean>，在属性注入时，类型转换肯定是引用类型。我们来跟踪一下代码，如图所示：

![Center 10][]

是走引用类型路线，这时会调用genBean（），进行对引用类进行实例化，这都是交给IOC容器实现的，如图所示：

![Center 11][]

这时已经实例化好了，接下来就是注入进来，如图所示：

![Center 12][]

我们对Bean的实例化和属性解析并进行类型转换，例如依赖注入。

我们这里总结整个思路：

（1）先List<String> beanDefinitionNames获取BeanName，然后通过BeanName 获取Map<String, RootBeanDefinition> RootBeanDefinition，然后判断是否为单例、不是抽象、是为Lazy-init=false 然后调用getBean方法。

（2）如果BeanName是别名，先转换为原来的BeanName不是别名，然后如果缓存中有单例Bean时，就从缓存获取，如果没有的话，就创建一个

（3）先检查是否父工厂存在，如果有的话，获取父工厂

（4）判断Bean依赖对象所有的名称，如果有的话，获取依赖对象的名称，然后循环getBean（）；

（5）检查Bean的作用域，Scope 作用域、原型作用域、Request等，来实例化Bean ,是由FactoryBean是创建创建对象的工厂Bean，通过调用这个对象的 getObject 方法就能获取用户自定义产生的对象，从而为 Spring 提供了很好的扩展性。Spring 获取 FactoryBean 本身的对象是在前面加上 & 来完成的。

（6）封装Bean，用 BeanWrapper是对Bean的包装，其接口中所定义的功能很简单包括设置获取被包装的对象，获取被包装bean的属性描述器，由于BeanWrapper接口是PropertyAccessor的子接口，因此其也可以设置以及访问被包装对象的属性值。BeanWrapper大部分情况下是在IOC内部进行使用，通过BeanWrapper,IOC容器可以用统一的方式来访问Bean的属性。

（7）根据BeanName去容器缓存中获取已经Bean的包装好的BeanWrapper，如果没有就调用createBeanInstance(beanName, mbd, args)，实例化Bean

(8)获取BeanWrapper里已经实例好的Bean，然后放到缓存，这样下次已经有了，就不用在创建。

（9）设置Bean实例的属性,对需要转换的属性进行转换，例如数组等，如果属性是引用类型，如果引用Bean没实例化，要在实例化，把bean实例对象封装好依赖注入在注入进来。

我这边介绍的主要是配置文件的xml中的配置bean。对注解的@Autowire,@Service@Controller等怎么实例化，和依赖注入等怎么使用，我们在SpringMVC中大部分都是用注解来开发，方便我们使用。我们带着这些问题，下一篇继续解析。

[Bean]: http://blog.csdn.net/congcong68/article/details/40650143
[Center]: /images/20220810/11defea1cd0c4fe8997c741e8fff3fb2.png
[Center 1]: /images/20220810/e668cf0ed86c4a2a8313444a83f0681b.png
[BeanWrapper]: http://blog.csdn.net/congcong68/article/details/40626563
[Center 2]: /images/20220810/1cdc0630071a412f917bc7ab34ef8d78.png
[Center 3]: /images/20220810/c7fdef59c7a54c47ba7dc2bb839b66a8.png
[Center 4]: /images/20220810/c0e2405446984a7fb92f16933b8846a5.png
[Center 5]: /images/20220810/606666bd419549fd891530e00af793af.png
[Center 6]: /images/20220810/f64aceadd4514b90bc45a57377870272.png
[Center 7]: /images/20220810/10305b2e288546c18682f3f87bc180f0.png
[Center 8]: /images/20220810/a5de4d37e6ba43aeb07794e8c1239ffe.png
[Center 9]: /images/20220810/c3f27ad56cbb40e7adae48ff82afc1a6.png
[Center 10]: /images/20220810/ac5f3d0554c0443fb514540caaf70299.png
[Center 11]: /images/20220810/5e012712e063447db1b6cfe6d817f11d.png
[Center 12]: /images/20220810/939641ae0ee6414eb4a5cacc68fd1fd0.png