Spring源码分析4 — spring bean创建和初始化
2017-07-14 17:23
627 查看
1 介绍
创建并初始化spring容器中,refresh()方法中解析xml配置文件,注册容器后处理器,bean后处理器,初始化MessageSource,ApplicationEventMulticaster广播器,注册完ApplicationListener监听器后,关键一步就是创建和初始化其他非lazy-init的singleton beans。这样在容器初始化好的时候,这些singleton beans就已经创建和初始化好了,可以大大提高bean的访问效率。这个过程比较复杂,本文将详细分析整个流程。先看涉及到的关键类。AbstractApplicationContext: 定义了spring容器初始化的大部分流程方法,子类必须遵循这个流程,但可以修改流程中的方法,典型的模板模式。bean创建的入口方法finishBeanFactoryInitialization也在这个方法中。
DefaultListableBeanFactory:一种BeanFactory容器实现,实现了ConfigurableListableBeanFactory接口
BeanDefinition:描述bean结构,对应XML中的或者注解中的@Component
AbstractBeanFactory:继承了BeanFactory容器,主要负责getBean创建Bean实例。
2 流程
2.1 finishBeanFactoryInitialization
初始化spring容器中的refresh()方法中,会调用finishBeanFactoryInitialization()方法,它是创建和初始化其他非lazy-init的singleton的bean的入口。下面从这个方法开始分析。protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) { // 初始化conversionService类型转换bean,它可以服务于其他bean的类型转换 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)); } // 注册字符串解析器,用来解析注解中的属性 if (!beanFactory.hasEmbeddedValueResolver()) { beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal)); } // 初始化LoadTimeWeaverAware bean String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false); for (String weaverAwareName : weaverAwareNames) { getBean(weaverAwareName); } // 停止使用临时的ClassLoader, beanFactory.setTempClassLoader(null); beanFactory.freezeConfiguration(); // 这儿才是最关键的一步,创建和初始化非lazy-init的singleton beans beanFactory.preInstantiateSingletons(); }
finishBeanFactoryInitialization()做了初始化conversionService类型转换器等的工作,这些不是关键点。关键点在preInstantiateSingletons()方法中,它会做创建和初始化singleton bean的工作。下面接着分析
public void preInstantiateSingletons() throws BeansException { // 获取XML配置文件解析时,解析到的所有beanname List<String> beanNames = new ArrayList<>(this.beanDefinitionNames); // 遍历所有没有标注lazy-init的singleton的beanname,创建bean for (String beanName : beanNames) { // 利用beanname获取BeanDefinition,在XML解析时会生成BeanDefinition对象,将XML中的各属性添加到BeanDefinition的相关标志位中,比如abstractFlag,scope等 RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName); // 非abstract,非lazy-init的singleton bean才需要在容器初始化阶段创建 if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) { // 处理FactoryBean if (isFactoryBean(beanName)) { // 获取FactoryBean实例,FactoryBean前面会加一个&符号 final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName); boolean isEagerInit; if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) { isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>) () -> ((SmartFactoryBean<?>) factory).isEagerInit(), getAccessControlContext()); } else { isEagerInit = (factory instanceof SmartFactoryBean && ((SmartFactoryBean<?>) factory).isEagerInit()); } if (isEagerInit) { getBean(beanName); } } // 非Factorybean,直接调用getBean方法,关键所在,后续分析 else { getBean(beanName); } } } // bean创建后,对SmartInitializingSingleton回调afterSingletonsInstantiated()方法,这儿不用太care for (String beanName : beanNames) { Object singletonInstance = getSingleton(beanName); if (singletonInstance instanceof SmartInitializingSingleton) { final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance; if (System.getSecurityManager() != null) { AccessController.doPrivileged((PrivilegedAction<Object>) () -> { smartSingleton.afterSingletonsInstantiated(); return null; }, getAccessControlContext()); } else { smartSingleton.afterSingletonsInstantiated(); } } } }
preInstantiateSingletons流程稍微复杂点,主要有
获取XML解析时的beanNames
遍历beanNames,获取BeanDefinition。对非abstract,非lazy-init的singleton bean的进行实例化
如果是FactoryBean,则需要判断isEagerInit,来确定是否调用getBean创建对应的bean。
如果不是,则直接调用getBean创建对应bean
bean创建后,对SmartInitializingSingleton回调afterSingletonsInstantiated()方法。
2.2 getBean 创建和初始化bean实例
下面我们着重来分析bean的创建,也就是getBean()方法。public Object getBean(String name) throws BeansException { return doGetBean(name, null, null, false); }
protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType, @Nullable final Object[] args, boolean typeCheckOnly) throws BeansException { // beanname转换,去掉FactoryBean的&前缀,处理alias声明。细节可自行分析 final String beanName = transformedBeanName(name); Object bean; Object sharedInstance = getSingleton(beanName); if (sharedInstance != null && args == null) { // 判断singleton bean是否已经创建好了,创建好了则直接从内存取出。 bean = getObjectForBeanInstance(sharedInstance, name, beanName, null); } else { // 之前没创建的,则需要创建。 // 正在创建,则直接异常返回 if (isPrototypeCurrentlyInCreation(beanName)) { throw new BeanCurrentlyInCreationException(beanName); } // 检查是否有beanname对应的BeanDefinition BeanFactory parentBeanFactory = getParentBeanFactory(); if (parentBeanFactory != null && !containsBeanDefinition(beanName)) { // 没有找到BeanDefinition,看看parent工厂中有没有,调用parent工厂的getBean // 获取原始的name,包含了FactoryBean前缀,&符号 String nameToLookup = originalBeanName(name); if (parentBeanFactory instanceof AbstractBeanFactory) { return ((AbstractBeanFactory) parentBeanFactory).doGetBean( nameToLookup, requiredType, args, typeCheckOnly); } else if (args != null) { return (T) parentBeanFactory.getBean(nameToLookup, args); } else { return parentBeanFactory.getBean(nameToLookup, requiredType); } } if (!typeCheckOnly) { markBeanAsCreated(beanName); } try { // 找到了beanname对应的BeanDefinition,合并parent的BeanDefinition(XML中的parent属性) final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName); checkMergedBeanDefinition(mbd, beanName, args); // 处理dependsOn属性 String[] dependsOn = mbd.getDependsOn(); if (dependsOn != null) { // 遍历所有的dependOn bean,要先注册和创建依赖的bean for (String dep : dependsOn) { // check是否两个bean是循环依赖,spring不能出现bean的循环依赖 if (isDependent(beanName, dep)) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Circular depends-on relationship between '" + beanName + "' and '" + dep + "'"); } // 注册并创建依赖的bean registerDependentBean(dep, beanName); getBean(dep); } } // 处理scope属性 if (mbd.isSingleton()) { // singleton, 必须保证线程安全情况下创建bean,保证单例 sharedInstance = getSingleton(beanName, () -> { try { // 反射创建bean实例,这个过程很复杂,稍后分析 return createBean(beanName, mbd, args); } catch (BeansException ex) { // 异常处理,清除掉bean destroySingleton(beanName); throw ex; } }); // 获取bean实例 bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd); } else if (mbd.isPrototype()) { // prototype,创建一个全新的实例 Object prototypeInstance = null; try { // 创建前的回调 beforePrototypeCreation(beanName); // 反射创建bean实例,稍后详细分析 prototypeInstance = createBean(beanName, mbd, args); } finally { // 创建后的回调,清除inCreation的标志 afterPrototypeCreation(beanName); } bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd); } else { // 其他scope值 String scopeName = mbd.getScope(); final Scope scope = this.scopes.get(scopeName); if (scope == null) { // scope属性不能接收空值 throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'"); } try { Object scopedInstance = scope.get(beanName, () -> { 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 创建的bean是否是requiredType指明的类型。如果不是,先做转换,转换不成的话只能类型不匹配抛出异常了 if (requiredType != null && bean != null && !requiredType.isInstance(bean)) { try { // 尝试将创建的bean转换为requiredType指明的类型 return getTypeConverter().convertIfNecessary(bean, requiredType); } catch (TypeMismatchException ex) { // 转换不成功,抛出异常 throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass()); } } return (T) bean; }
doGetBean概括了bean创建和初始化的主要流程,十分复杂,步骤主要为
beanname转换,去掉FactoryBean的&前缀,处理alias声明
判断singleton bean是否已经创建好了,创建好了则直接从内存取出
没有创建好,则检查是否有beanname对应的BeanDefinition,没有则到parent工厂中查找,命中则使用parent工厂再次调用getBean以及doGetBean创建
有BeanDefinition,则合并parent属性指向的中的属性,这主要是处理bean的parent属性。子bean会继承parent bean的属性。
处理dependsOn属性。必须先创建好所有的依赖的bean
处理scope属性,如果是singleton的,则必须保证线程安全情况下创建单例。如果是prototype,则必须保证创建一个全新的bean。创建bean通过createBean()反射创建。
2.3 createBean 反射创建bean实例
下面来分析createBean()方法,这个过程也是相当复杂的。protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) throws BeanCreationException { RootBeanDefinition mbdToUse = mbd; // 拷贝一个新的RootBeanDefinition供创建bean使用 Class<?> resolvedClass = resolveBeanClass(mbd, beanName); if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) { mbdToUse = new RootBeanDefinition(mbd); mbdToUse.setBeanClass(resolvedClass); } // 处理bean中定义的覆盖方法,主要是xml:lookup-method或replace-method。标记override的方法为已经加载过的,避免不必要的参数检查开销。这儿不详细展开了。 try { mbdToUse.prepareMethodOverrides(); } catch (BeanDefinitionValidationException ex) { throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(), beanName, "Validation of method overrides failed", ex); } // 调用BeanPostProcessors bean后处理器,使得bean后处理器可以返回一个proxy bean,从而代替我们要创建的bean。回调后处理器的postProcessBeforeInstantiation()方法,如果这个方法中返回了一个bean,也就是使用了proxy,则再回调postProcessAfterInitialization()方法。之后返回这个Proxy bean即可。 try { Object bean = resolveBeforeInstantiation(beanName, mbdToUse); if (bean != null) { return bean; } } catch (Throwable ex) { throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName, "BeanPostProcessor before instantiation of bean failed", ex); } // doCreateBean创建bean实例,后面详细分析 try { Object beanInstance = doCreateBean(beanName, mbdToUse, args); return beanInstance; } // 各种异常,省略 ... }
createBean()方法大概步骤如下
拷贝一个新的RootBeanDefinition供创建bean使用
处理lookup-method或replace-method
调用BeanPostProcessors后处理器
doCreateBean创建bean实例
下面我们重点分析doCreateBean方法
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args) throws BeanCreationException { // 创建bean实例,如果是singleton,先尝试从缓存中取,取不到则创建 BeanWrapper instanceWrapper = null; if (mbd.isSingleton()) { instanceWrapper = this.factoryBeanInstanceCache.remove(beanName); } if (instanceWrapper == null) { // 反射创建bean实例,后面详细说 instanceWrapper = createBeanInstance(beanName, mbd, args); } final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null); Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null); mbd.resolvedTargetType = beanType; // 回调MergedBeanDefinitionPostProcessor.postProcessMergedBeanDefinition,它可以修改bean属性 if (beanType != null) { synchronized (mbd.postProcessingLock) { if (!mbd.postProcessed) { try { applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName); } catch (Throwable ex) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Post-processing of merged bean definition failed", ex); } mbd.postProcessed = true; } } } // 曝光单例对象的引用,主要是为了解决单例间的循环依赖问题,以及依赖的bean比较复杂时的初始化性能问题 boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences && isSingletonCurrentlyInCreation(beanName)); if (earlySingletonExposure) { addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean)); } // 初始化bean,后面详细介绍 Object exposedObject = bean; try { populateBean(beanName, mbd, instanceWrapper); if (exposedObject != null) { exposedObject = initializeBean(beanName, exposedObject, mbd); } } // 省略异常处理 // 单例曝光对象的处理,不用太在意 if (earlySingletonExposure) { 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<>(dependentBeans.length); for (String dependentBean : dependentBeans) { if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) { actualDependentBeans.add(dependentBean); } } if (!actualDependentBeans.isEmpty()) { // 抛出异常,省略代码 } } } } // 注册bean为可销毁的bean,bean销毁时,会回调destroy-method if (bean != null) { try { registerDisposableBeanIfNecessary(beanName, bean, mbd); } catch (BeanDefinitionValidationException ex) { throw new BeanCreationException( mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex); } } return exposedObject; }
doCreateBean方法主要流程为
createBeanInstance() 创建bean实例
回调postProcessMergedBeanDefinition(), 可以修改bean属性
initializeBean() 初始化bean实例,包括后处理器的调用,init-method的调用等
注册bean为可销毁的,这样在bean销毁时,就可以回调到destroy-method.
2.3.1 createBeanInstance 反射创建bean实例
我们先分析如何创建bean实例的。个protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) { // 先创建class对象,反射的套路。利用bean的class属性进行反射,所以class属性一定要是bean的实现类 Class<?> beanClass = resolveBeanClass(mbd, beanName); // class如果不是public的,则抛出异常。因为没法进行实例化 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()); } // Supplier<?> instanceSupplier = mbd.getInstanceSupplier(); if (instanceSupplier != null) { return obtainFromSupplier(instanceSupplier, beanName); } // 使用FactoryBean的factory-method来创建,支持静态工厂和实例工厂 if (mbd.getFactoryMethodName() != null) { return instantiateUsingFactoryMethod(beanName, mbd, args); } // 无参数情况时,创建bean。调用无参构造方法 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) { // autoWire创建 自动装配 return autowireConstructor(beanName, mbd, null, null); } else { // 普通创建 return instantiateBean(beanName, mbd); } } // 有参数情况时,创建bean。先利用参数个数,类型等,确定最精确匹配的构造方法。 Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName); if (ctors != null || mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR || mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) { return autowireConstructor(beanName, mbd, ctors, args); } // 有参数时,又没获取到构造方法,则只能调用无参构造方法来创建实例了(兜底方法) return instantiateBean(beanName, mbd); }
instantiateBean,使用无参构造方法,反射创建bean实例代码如下
protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) { try { Object beanInstance; final BeanFactory parent = this; if (System.getSecurityManager() != null) { beanInstance = AccessController.doPrivileged((PrivilegedAction<Object>) () -> getInstantiationStrategy().instantiate(mbd, beanName, parent), getAccessControlContext()); } else { // 创建实例,关键点,其他都不用care 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); } }
这个方法没什么要注意的,关键点在instantiate方法
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) { // Don't override the class with CGLIB if no overrides. if (bd.getMethodOverrides().isEmpty()) { Constructor<?> constructorToUse; // 保证线程安全情况下,获取Constructor synchronized (bd.constructorArgumentLock) { // 获取构造方法或factory-method constructorToUse = (Constructor<?>) bd.resolvedConstructorOrFactoryMethod; if (constructorToUse == null) { // BeanDefinition中如果没有Constructor或者factory-method,则直接使用默认无参构造方法。 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( (PrivilegedExceptionAction<Constructor<?>>) () -> clazz.getDeclaredConstructor()); } else { // 获取默认无参构造方法 constructorToUse = clazz.getDeclaredConstructor(); } bd.resolvedConstructorOrFactoryMethod = constructorToUse; } catch (Throwable ex) { throw new BeanInstantiationException(clazz, "No default constructor found", ex); } } } // 使用上一步得到的Constructor,反射获取bean实例 return BeanUtils.instantiateClass(constructorToUse); } else { // Must generate CGLIB subclass. return instantiateWithMethodInjection(bd, beanName, owner); } }
instantiate方法主要做两件事
确定Constructor或者factory-method
利用Constructor,反射创建bean实例。
分析到这儿Bean的创建就结束了,这个过程实在是太复杂了!
2.3.2 initializeBean 初始化bean实例
bean创建完后,容器会对它进行初始化,包括后处理的调用,init-method的调用等。请看下面详解。protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) { // 回调各种aware method,如BeanNameAware, BeanFactoryAware等 if (System.getSecurityManager() != null) { AccessController.doPrivileged((PrivilegedAction<Object>) () -> { invokeAwareMethods(beanName, bean); return null; }, getAccessControlContext()); } else { invokeAwareMethods(beanName, bean); } // 回调beanPostProcessor的postProcessBeforeInitialization()方法 Object wrappedBean = bean; if (mbd == null || !mbd.isSynthetic()) { wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName); } // init-method 和 postProcessAfterInitialization if (wrappedBean != null) { try { // 回调init-method invokeInitMethods(beanName, wrappedBean, mbd); } catch (Throwable ex) { throw new BeanCreationException( (mbd != null ? mbd.getResourceDescription() : null), beanName, "Invocation of init method failed", ex); } // 回调beanPostProcessor的postProcessAfterInitialization()方法 if (mbd == null || !mbd.isSynthetic()) { wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName); } } return wrappedBean; }
由此可见,initializeBean(),也就是bean的初始化流程为
回调各种aware method,如BeanNameAware,将容器中相关引用注入到bean中,供bean使用
回调beanPostProcessor的postProcessBeforeInitialization(), 后处理器的初始化前置调用
回调init-method, 注解和XML中都可以声明
回调beanPostProcessor的postProcessAfterInitialization()方法,后处理器的初始化后置调用。
从这个流程,我们也能清晰的分析出容器后处理器两个方法的调用时机。分析源码可以大大加深我们对spring API的理解。
3 总结
Bean实例的创建和初始化流程还是十分复杂的。从源码中可以清晰的分析出spring bean的各种特性。如factory-method, BeanPostProcessor等。有助于我们spring bean行为的理解。所以分析源码还是十分值得的。相关文章推荐
- Spring源码分析3 — spring bean创建和初始化
- Spring源码解析:Bean实例的创建与初始化
- spring源码分析(1)——AnnotatedBeanDefinitionReader和ClassPathBeanDefinitionScanner的初始化
- Spring IoC源码解析——Bean的创建和初始化
- Spring IOC容器bean初始化源码分析
- Spring源码分析:非懒加载的单例Bean初始化前后的一些操作
- Spring源码分析-2-创建Bean
- Spring Ioc创建之BeanFactory创建源码分析
- Spring 源码分析《Bean的获取与创建流程》
- spring 源码探索--创建bean实例和初始化
- 【Spring源码分析】非懒加载的单例Bean初始化过程(上篇)
- Spring源码分析:非懒加载的单例Bean初始化过程(上)
- Spring IOC 容器源码分析 - 创建单例 bean 的过程
- 2、Spring的LocalSessionFactoryBean创建过程源码分析
- 【Spring源码分析】非懒加载的单例Bean初始化过程(下篇)
- Spring源码分析:非懒加载的单例Bean初始化过程(下)
- 分析spring源码第五(三)篇:Spring中Bean的解析、加载、创建 过程总结
- Spring IOC 容器源码分析 - 创建原始 bean 对象
- 【Spring源码分析】非懒加载的单例Bean初始化前后的一些操作
- 【简记】Java Web 内幕——Spring源码(组件分析,BeanFactory源码,Bean创建之前)