spring源码解析-Bean的实例化

在上一章我们已经获取到了 BeanDefinition ,现在就可以开始对Bean进行实例化的操作了

Bean的实例化分为两种情况延迟加载和非延迟加载

这里只分析非延迟加载的情况

Bean的实例化操作是在 AbstractApplicationContext#refresh 中的 finishBeanFactoryInitialization 方法中进行

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protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
		// 设置转换器
		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));
		}

        //省略部份代码

				// 处理代码织入
				String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
		for (String weaverAwareName : weaverAwareNames) {
			getBean(weaverAwareName);
		}
		// 准备初始化非懒加载Bean
		beanFactory.preInstantiateSingletons();
	}

可以看出其中关键方法为 preInstantiateSingletons

Bean实例化时序图

可以看出核心是 instantiateBean 和 applyPropertyValues 方法

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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>() {
					@Override
					public Object run() {
					//策略模式默认调用CglibSubclassingInstantiationStrategy
						return getInstantiationStrategy().instantiate(mbd, beanName, parent);
					}
				}, getAccessControlContext());
			}
			else {
				beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);
			}
			//BeanWrapper是实例Bean的再次包装
			BeanWrapper bw = new BeanWrapperImpl(beanInstance);
			initBeanWrapper(bw);
			return bw;
		}
		catch (Throwable ex) {
			throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex);
		}
	}

再看 SimpleInstantiationStrategy#instantiate(RootBeanDefinition, String,BeanFactory) 方法

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public Object instantiate(RootBeanDefinition bd, String beanName, BeanFactory owner) {
		// Don't override the class with CGLIB if no overrides.
		if (bd.getMethodOverrides().isEmpty()) {
			Constructor<?> constructorToUse;
			synchronized (bd.constructorArgumentLock) {
			//获取构造方法或者工厂方法
				constructorToUse = (Constructor<?>) bd.resolvedConstructorOrFactoryMethod;
				if (constructorToUse == null) {
					final Class<?> clazz = bd.getBeanClass();
					if (clazz.isInterface()) {
						throw new BeanInstantiationException(clazz, "Specified class is an interface");
					}
					try {
						if (System.getSecurityManager() != null) {
							constructorToUse = AccessController.doPrivileged(new PrivilegedExceptionAction<Constructor<?>>() {
								@Override
								public Constructor<?> run() throws Exception {
									return clazz.getDeclaredConstructor((Class[]) null);
								}
							});
						}
						else {
							constructorToUse =	clazz.getDeclaredConstructor((Class[]) null);
						}
						bd.resolvedConstructorOrFactoryMethod = constructorToUse;
					}
					catch (Throwable ex) {
						throw new BeanInstantiationException(clazz, "No default constructor found", ex);
					}
				}
			}
			//使用BeanUtils实例化,里面调用的是构造方法实例化
			return BeanUtils.instantiateClass(constructorToUse);
		}
		else {
		//CglibSubclassingInstantiationStrategy重写了该方法,使用cglib实例化
			return instantiateWithMethodInjection(bd, beanName, owner);
		}
	}

具体的cglib方法就不展开了,对象实例化之后还需要将其属性填充进去,并完成依赖关系的处理,这个过程叫依赖注入

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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());
			}
		}

		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 {
			original = Arrays.asList(pvs.getPropertyValues());
		}
//自定义类型转换器
		TypeConverter converter = getCustomTypeConverter();
		if (converter == null) {
			converter = bw;
		}
		BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);

		//创建副本用于转换及注入到Bean中
		List<PropertyValue> deepCopy = new ArrayList<PropertyValue>(original.size());
		boolean resolveNecessary = false;
		for (PropertyValue pv : original) {
			if (pv.isConverted()) {
				deepCopy.add(pv);
			}
			else {
				String propertyName = pv.getName();
				Object originalValue = pv.getValue();
				//通过属性获取值,并处理依赖关系
				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();
		}

		// 参数注入的地方
		try {
			bw.setPropertyValues(new MutablePropertyValues(deepCopy));
		}
		catch (BeansException ex) {
			throw new BeanCreationException(
					mbd.getResourceDescription(), beanName, "Error setting property values", ex);
		}
	}

处理依赖关系的方法 BeanDefinitionValueResolver#resolveValueIfNecessary

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public Object resolveValueIfNecessary(Object argName, Object value) {
		//如果该Bean被其它对象依赖时
		if (value instanceof RuntimeBeanReference) {
			RuntimeBeanReference ref = (RuntimeBeanReference) value;
			return resolveReference(argName, ref);
		}
		else if (value instanceof RuntimeBeanNameReference) {
			//省略源码
		}
		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) {
			//省略源码
			return resolveInnerBean(argName, innerBeanName, bd);
		}
		else if (value instanceof ManagedArray) {
			//省略源码
			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) {
			//省略源码
			return copy;
		}
		else if (value instanceof TypedStringValue) {
			//省略源码
		}
		else {
			return evaluate(value);
		}
	}

	private Object resolveInnerBean(Object argName, String innerBeanName, BeanDefinition innerBd) {
		RootBeanDefinition mbd = null;
		try {
			mbd = this.beanFactory.getMergedBeanDefinition(innerBeanName, innerBd, this.beanDefinition);
			// Check given bean name whether it is unique. If not already unique,
			// add counter - increasing the counter until the name is unique.
			String actualInnerBeanName = innerBeanName;
			if (mbd.isSingleton()) {
				actualInnerBeanName = adaptInnerBeanName(innerBeanName);
			}
			this.beanFactory.registerContainedBean(actualInnerBeanName, this.beanName);
			// 确保依赖的Bean已经被实例化
			String[] dependsOn = mbd.getDependsOn();
			if (dependsOn != null) {
				// 获取依赖的Bean,如果没有被创建该方法会自动创建
				for (String dependsOnBean : dependsOn) {
					this.beanFactory.registerDependentBean(dependsOnBean, actualInnerBeanName);
					this.beanFactory.getBean(dependsOnBean);
				}
			}
			//开始实例化Bean
			Object innerBean = this.beanFactory.createBean(actualInnerBeanName, mbd, null);
			if (innerBean instanceof FactoryBean) {
				boolean synthetic = mbd.isSynthetic();
				return this.beanFactory.getObjectFromFactoryBean(
						(FactoryBean<?>) innerBean, actualInnerBeanName, !synthetic);
			}
			else {
				return innerBean;
			}
		}
		catch (BeansException ex) {
			throw new BeanCreationException(
					this.beanDefinition.getResourceDescription(), this.beanName,
					"Cannot create inner bean '" + innerBeanName + "' " +
					(mbd != null && mbd.getBeanClassName() != null ? "of type [" + mbd.getBeanClassName() + "] " : "") +
					"while setting " + argName, ex);
		}
	}

参数注入 AbstractNestablePropertyAccessor#setPropertyValue(AbstractNestablePropertyAccessor.PropertyTokenHolder, PropertyValue) 方法比较长,就不贴了,主要是对集合类和非集合类的注入

对集合类

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//如果是list类型
if (propValue instanceof List) {
				PropertyHandler ph = getPropertyHandler(actualName);
				Class<?> requiredType = ph.getCollectionType(tokens.keys.length);
				List<Object> list = (List<Object>) propValue;
				int index = Integer.parseInt(key);
				Object oldValue = null;
				if (isExtractOldValueForEditor() && index < list.size()) {
					oldValue = list.get(index);
				}
				//如果有对应参数转换器则将原值转换
				Object convertedValue = convertIfNecessary(propertyName, oldValue, pv.getValue(),
						requiredType, ph.nested(tokens.keys.length));
				int size = list.size();
				if (index >= size && index < this.autoGrowCollectionLimit) {
					for (int i = size; i < index; i++) {
						try {
							list.add(null);
						}
						catch (NullPointerException ex) {
							throw new InvalidPropertyException(getRootClass(), this.nestedPath + propertyName,
									"Cannot set element with index " + index + " in List of size " +
									size + ", accessed using property path '" + propertyName +
									"': List does not support filling up gaps with null elements");
						}
					}
					//如果超出原有长度,则新增数据
					list.add(convertedValue);
				}
				else {
				//替换原有值
					try {
						list.set(index, convertedValue);
					}
					catch (IndexOutOfBoundsException ex) {
						throw new InvalidPropertyException(getRootClass(), this.nestedPath + propertyName,
								"Invalid list index in property path '" + propertyName + "'", ex);
					}
				}
			}

对非集合类 org.springframework.beans.BeanWrapperImpl.BeanPropertyHandler#setValue 方法使用反射注入参数

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public void setValue(final Object object, Object valueToApply) throws Exception {
			final Method writeMethod = (this.pd instanceof GenericTypeAwarePropertyDescriptor ?
					((GenericTypeAwarePropertyDescriptor) this.pd).getWriteMethodForActualAccess() :
					this.pd.getWriteMethod());
			if (!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers()) && !writeMethod.isAccessible()) {
				if (System.getSecurityManager() != null) {
					AccessController.doPrivileged(new PrivilegedAction<Object>() {
						@Override
						public Object run() {
							writeMethod.setAccessible(true);
							return null;
						}
					});
				}
				else {
					writeMethod.setAccessible(true);
				}
			}
			final Object value = valueToApply;
			if (System.getSecurityManager() != null) {
				try {
					AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
						@Override
						public Object run() throws Exception {
							writeMethod.invoke(object, value);
							return null;
						}
					}, acc);
				}
				catch (PrivilegedActionException ex) {
					throw ex.getException();
				}
			}
			else {
				writeMethod.invoke(getWrappedInstance(), value);
			}
		}

到这一步Bean的实例化就结束了

bean实例化相关结构

文章目录