SpringIOC初始化过程
相信大家都知道Spring这个东西，我们经常来用他一些特性，比如说他的AOP，IOC，那今天就带大家解析下SpringIOC的加载过程。
我们来看一个例子
AnnotationConfigApplicationContext context=new AnnotationConfigApplicationContext(JobService.class); for (String beanname:context.getBeanDefinitionNames()) { System.out.println("--------"+beanname); } System.out.println("context.getBean(JobService.class) = " + context.getBean(JobService.class));
这点代码很简单 初始化bean，然后再来拿bean，我们点进AnnotationConfigApplicationContext来看
public AnnotationConfigApplicationContext(Class<?>... annotatedClasses) { this(); register(annotatedClasses); refresh(); }
进⼊之后 会调用 this()默认无参构造方法
public AnnotationConfigApplicationContext() { this.reader = new AnnotatedBeanDefinitionReader(this); this.scanner = new ClassPathBeanDefinitionScanner(this); }
调⽤这个⽆参构造⽅法的同时 他会调用⽗类的构造方法，在调用父类构造⽅方法时 他new了一个对象
public GenericApplicationContext() { this.beanFactory = new DefaultListableBeanFactory(); }
也就是 DefaultListableBeanFactory，当然 这个就是所谓我们平常所说的 bean工厂，其父类就是 BeanFactory，BeanFactory有很多子类，DefaultListableBeanFactory就是其中一个⼦类。 那么 bean的⽣命周期是围绕那个⽅法呢，就是refresh()⽅法。也就是bean的整个生命周期是围绕refresh() 来进行的
在refresh()我们可以看到
public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // 准备好刷新上下文. prepareRefresh(); // 返回一个Factory 为什么需要返回一个工厂 因为要对工厂进行初始化 ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // 准备bean工厂，以便在此上下文中使用。 prepareBeanFactory(beanFactory); try { // 允许在上下文子类中对bean工厂进行后处理。 在spring5 并未对此接口进行实现 postProcessBeanFactory(beanFactory); // 在spring的环境中去执行已经被注册的 Factory processors //设置执行自定义的postProcessBeanFactory和spring内部自己定义的 invokeBeanFactoryPostProcessors(beanFactory); // 注册postProcessor registerBeanPostProcessors(beanFactory); // 初始化此上下文的消息源。 initMessageSource(); // 初始化此上下文的事件多播程序。 initApplicationEventMulticaster(); // 在特定上下文子类中初始化其他特殊bean。 onRefresh(); //检查侦听器bean并注册它们。 registerListeners(); // 实例化所有剩余的(非懒加载)单例。 //new 单例对象 finishBeanFactoryInitialization(beanFactory); // 最后一步:发布相应的事件 finishRefresh(); } catch (BeansException ex) { if (logger.isWarnEnabled()) { logger.warn("Exception encountered during context initialization - " + "cancelling refresh attempt: " + ex); } // Destroy already created singletons to avoid dangling resources. destroyBeans(); // Reset 'active' flag. cancelRefresh(ex); // Propagate exception to caller. throw ex; } finally { // Reset common introspection caches in Spring's core, since we // might not ever need metadata for singleton beans anymore... resetCommonCaches(); } } }
那么这里面最重要就是finishBeanFactoryInitialization(beanFactory);这个方法就是描述 spring的一个bean如何初始化
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) { // Initialize conversion service for this context. 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)); } // Register a default embedded value resolver if no bean post-processor // (such as a PropertyPlaceholderConfigurer bean) registered any before: // at this point, primarily for resolution in annotation attribute values. if (!beanFactory.hasEmbeddedValueResolver()) { beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal)); } // 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(); // 实例化所有单例对象 beanFactory.preInstantiateSingletons(); }
@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. //所有bean的名字 List<String> beanNames = new ArrayList<>(this.beanDefinitionNames); // Trigger initialization of all non-lazy singleton beans... for (String beanName : beanNames) { RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName); if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) { if (isFactoryBean(beanName)) { Object bean = getBean(FACTORY_BEAN_PREFIX + beanName); if (bean instanceof FactoryBean) { final FactoryBean<?> factory = (FactoryBean<?>) bean; 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); } } } else { getBean(beanName); } } }
我们可以看到用
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
来保存bean的名字，那this.beanDefinitionNames是一个什么东西
/** List of bean definition names, in registration order */ private volatile List<String> beanDefinitionNames = new ArrayList<>(256);
可以看到是beanDefinition的一个名字，那beanDefinition是个什么呢？它是spring当中非常重要的一个概念，在这里简单的提一嘴 我们传统用纯java的方式怎么new对象 是 Student stu=new Student();的方式来实例化对象，但是要交给spring的话，
先通过springScan的方式扫描到类，当他扫描到的时候 他会去new一个beanDefinition对象 他有很多子类 比如说 GenericBeanDefinition generic=new GenericBeanDefinition();然后他会把扫描到的类的各种信息给拿出来，比如说Student的名字是什么：
GenericBeanDefinition generic=new GenericBeanDefinition(); generic.setBeanClassName("studentService"); 类的名字 generic.setBeanClass(StudentService.class); 类路径 generic.isSingleton(); 包括是单例还是原型
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(256);
就放到这个Map当中 也就是
beanDefinitionMap.put("studentService",generic)这样放进去之后，spring会看你有没有调用拓展接口，拓展接口我们到后面再说 如果没有拓展接口，就会继续调用我们刚刚接着继续的 preInstantiateSingletons()方法，这个方法来完成bean的实例化 总的一句话 BeanDefinition就是用来描述bean的，当然BeanDefinition的知识不仅仅是这些，今天只是简单提一嘴
那么我们现在继续 beanDefinitionNames也就是刚刚那个Map中Key的集合，然后开始循环
//触发所有非延迟加载单例beans的初始化，只要步骤调用getBean //根据List名字从Map当中把BeanDefinition依次拿出来开始new对象 for (String beanName : beanNames) { //合并父BeanDefinition //通过Map的名字拿BeanDefinition RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName); //判断当前类是否抽象 是否为单例 是否为懒加载 如果条件都成立 则继续 if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) { //判断该类是否为FactoryBean FactoryBean这里不进行讲解 不懂得朋友可以去了解下 //如果不是FactoryBean if (isFactoryBean(beanName)) { Object bean = getBean(FACTORY_BEAN_PREFIX + beanName); if (bean instanceof FactoryBean) { final FactoryBean<?> factory = (FactoryBean<?>) bean; 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); } } } else { //则直接调用getBean getBean(beanName); } } }
@Override //空方法 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 { /** *通过name获取beanName。这里不使用name直接做beanName * name可能会以&字符开头，表用调用者想获取FactoryBean本身，而非FactoryBean *实现类所创建的bean。在BeanFactory中，FactoryBean的实现类和其他的bean存储方式是一致的即 * <beanName, bean> ,beanName中没有&字符的。所以我们需要将name的首字母&移除，这样才能取到 *FactoryBean实例 */ final String beanName = transformedBeanName(name); Object bean; // Eagerly check singleton cache for manually registered singletons. 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); } // Check if bean definition exists in this factory. BeanFactory parentBeanFactory = getParentBeanFactory(); if (parentBeanFactory != null && !containsBeanDefinition(beanName)) { // Not found -> check parent. String nameToLookup = originalBeanName(name); if (parentBeanFactory instanceof AbstractBeanFactory) { return ((AbstractBeanFactory) parentBeanFactory).doGetBean( nameToLookup, requiredType, args, typeCheckOnly); } else 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 { final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName); checkMergedBeanDefinition(mbd, beanName, args); // 一个注解叫@DependsOn：A类创建 必须B类创建出来再创建A类 String[] dependsOn = mbd.getDependsOn(); if (dependsOn != null) { for (String dep : dependsOn) { if (isDependent(beanName, dep)) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Circular depends-on relationship between '" + beanName + "' and '" + dep + "'"); } registerDependentBean(dep, beanName); try { getBean(dep); } catch (NoSuchBeanDefinitionException ex) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "'" + beanName + "' depends on missing bean '" + dep + "'", ex); } } } // Create bean instance. if (mbd.isSingleton()) { //真正开始创建对象 sharedInstance = getSingleton(beanName, () -> { try { 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; } }); bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd); } else if (mbd.isPrototype()) { // It's a prototype -> create a new instance. Object prototypeInstance = null; try { beforePrototypeCreation(beanName); prototypeInstance = createBean(beanName, mbd, args); } finally { afterPrototypeCreation(beanName); } bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd); } else { String scopeName = mbd.getScope(); final Scope scope = this.scopes.get(scopeName); if (scope == null) { 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 if required type matches the type of the actual bean instance. if (requiredType != null && !requiredType.isInstance(bean)) { try { T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType); if (convertedBean == null) { throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass()); } return convertedBean; } 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; }
Object sharedInstance = getSingleton(beanName);重点为这行代码，我们点进去getSingleton(beanName)这个方法来看
@Override @Nullable public Object getSingleton(String beanName) { return getSingleton(beanName, true); } /** * Return the (raw) singleton object registered under the given name. * <p>Checks already instantiated singletons and also allows for an early * reference to a currently created singleton (resolving a circular reference). * @param beanName the name of the bean to look for * @param allowEarlyReference whether early references should be created or not * @return the registered singleton object, or {@code null} if none found */ @Nullable protected Object getSingleton(String beanName, boolean allowEarlyReference) { Object singletonObject = this.singletonObjects.get(beanName); if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) { synchronized (this.singletonObjects) { singletonObject = this.earlySingletonObjects.get(beanName); if (singletonObject == null && allowEarlyReference) { ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName); if (singletonFactory != null) { singletonObject = singletonFactory.getObject(); this.earlySingletonObjects.put(beanName, singletonObject); this.singletonFactories.remove(beanName); } } } } return singletonObject; }
正在要new一个对象的时候 他会调用getSingleton方法，那么在这个方法中
Object singletonObject = this.singletonObjects.get(beanName);
这行代码是本质，那他是什么东西 我们点进来看
/** Cache of singleton objects: bean name --> bean instance */ //用于存放完全初始化好的bean从该缓存中取出bean可以直接使用 private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256);
很明显 他就是个Map ConcurrentHashMap线程安全的Map，什么意思 这个Map也就是我们常常说说的Spring的容器 如果从微观角度来讲 没错spring容器就是这个Map，如果从宏观上讲，他就不能称之为map 我希望大家能理解什么意思，因为spring环境包含很多组件，各种组件包含在一起以及singletonObjects以及一些后置处理器配合完成一些工作我们称之为Spring容器。
singletonObjects 是什么？没错他就是单例池 他什么要在单例池拿？为什么要调用他？
因为他要解决Spring当中的循环依赖问题，相信大家既然有看源码的能力，相信大家也明白什么是循环依赖这里不再细说
在这个类里也有介绍
/** Cache of early singleton objects: bean name --> bean instance */ //存放原始的bean对象用于解决循环依赖，注意：存到里面的对象还没被填充到属性 private final Map<String, Object> earlySingletonObjects = new HashMap<>(16);
什么意思 一个bean放到singletonObjects之后，把一个对象new出来之后，如果这个对象要循环引用那spring就会先把他放到earlySingletonObjects这个当中.get是因为怕对象已经放到early当中所以先去get一遍，这里也只是简单题一嘴
那我们继续看
if (sharedInstance != null && args == null) {如果条件成立的话
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);直接返回调
如果条件不成立直接else
if (isPrototypeCurrentlyInCreation(beanName)) 判断这个类是否正在创建，什么意思 因为spring正在创建一类的时候他会进行标识这个类我正在创建中，然后获取bean工厂
BeanFactory parentBeanFactory = getParentBeanFactory();这里不重要
我们继续来看
sharedInstance = getSingleton(beanName, () -> { try { return createBean(beanName, mbd, args); } 到这一步的时候，才开始真正创建对象，这里又一个getSingleton这个方法跟上面那个不是同一个方法，这个地方用到lambdas表达式，我们点进去看这个getSingleton
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) { if (this.singletonsCurrentlyInDestruction) { throw new BeanCreationNotAllowedException(beanName, "Singleton bean creation not allowed while singletons of this factory are in destruction " + "(Do not request a bean from a BeanFactory in a destroy method implementation!)"); } if (logger.isDebugEnabled()) { logger.debug("Creating shared instance of singleton bean '" + beanName + "'"); } beforeSingletonCreation(beanName); boolean newSingleton = false; boolean recordSuppressedExceptions = (this.suppressedExceptions == null); if (recordSuppressedExceptions) { this.suppressedExceptions = new LinkedHashSet<>(); } try { singletonObject = singletonFactory.getObject(); newSingleton = true; } catch (IllegalStateException ex) { // Has the singleton object implicitly appeared in the meantime -> // if yes, proceed with it since the exception indicates that state. singletonObject = this.singletonObjects.get(beanName); if (singletonObject == null) { throw ex; } } catch (BeanCreationException ex) { if (recordSuppressedExceptions) { for (Exception suppressedException : this.suppressedExceptions) { ex.addRelatedCause(suppressedException); } } throw ex; } finally { if (recordSuppressedExceptions) { this.suppressedExceptions = null; } afterSingletonCreation(beanName); } if (newSingleton) { addSingleton(beanName, singletonObject); } } return singletonObject; } }
Object singletonObject = this.singletonObjects.get(beanName);
这里关键：
第一个getSingleton：单例池拿 拿不到到缓存池拿，拿不到返回null 第二个：也是先从单例池拿 如果为null， if (this.singletonsCurrentlyInDestruction)判断对象有没有开始创建，
然后 beforeSingletonCreation(beanName);我们点进去来看
protected void beforeSingletonCreation(String beanName) { if (!this.inCreationCheckExclusions.contains(beanName) && !this.singletonsCurrentlyInCreation.add(beanName)) { throw new BeanCurrentlyInCreationException(beanName); } }
singletonsCurrentlyInCreation是什么意思
/** Names of beans that are currently in creation */ private final Set<String> singletonsCurrentlyInCreation = Collections.newSetFromMap(new ConcurrentHashMap<>(16));
也是一个Lsit，什么意思 把它放到这个List当中表示正在创建
紧接着调用createBean(beanName, mbd, args);开始创建对象
我们来看createBean
@Override protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) throws BeanCreationException { if (logger.isDebugEnabled()) { logger.debug("Creating instance of bean '" + beanName + "'"); } RootBeanDefinition mbdToUse = mbd; // Make sure bean class is actually resolved at this point, and // clone the bean definition in case of a dynamically resolved Class // which cannot be stored in the shared merged bean definition. Class<?> resolvedClass = resolveBeanClass(mbd, beanName); if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) { mbdToUse = new RootBeanDefinition(mbd); mbdToUse.setBeanClass(resolvedClass); } // Prepare method overrides. try { mbdToUse.prepareMethodOverrides(); } catch (BeanDefinitionValidationException ex) { throw new BeanDefinitionStoreException(mbdToUse.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, mbdToUse); if (bean != null) { return bean; } } catch (Throwable ex) { throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName, "BeanPostProcessor before instantiation of bean failed", ex); } try { Object beanInstance = doCreateBean(beanName, mbdToUse, args); if (logger.isDebugEnabled()) { logger.debug("Finished creating instance of bean '" + beanName + "'"); } return beanInstance; } catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) { // A previously detected exception with proper bean creation context already, // or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry. throw ex; } catch (Throwable ex) { throw new BeanCreationException( mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex); } }
到这里 不要以为完了，其实还没完最重要的部分
Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
这个是第一次调用spring的后置处理器，spring的生命周期一共围绕了9个后置处理器，这个是第一个
我们先不管这些后置处理器是干嘛的 先把他找出来我们点进resolveBeforeInstantiation
@Nullable protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) { Object bean = null; if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) { // Make sure bean class is actually resolved at this point. if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) { Class<?> targetType = determineTargetType(beanName, mbd); if (targetType != null) { bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName); if (bean != null) { bean = applyBeanPostProcessorsAfterInitialization(bean, beanName); } } } mbd.beforeInstantiationResolved = (bean != null); } return bean; }
bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);点进来看
@Nullable protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) { for (BeanPostProcessor bp : getBeanPostProcessors()) { if (bp instanceof InstantiationAwareBeanPostProcessor) { InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp; Object result = ibp.postProcessBeforeInstantiation(beanClass, beanName); if (result != null) { return result; } } } return null; }
他会先拿出来所有后置处理器 然后判断是不是属于他
我们返回刚刚
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
在doCreateBean里面调用第二个后置处理器，我这里都不再一一寻找了，直接列出来吧
第一次：InstantiationAwareBeanPostProcessor --postProcessBeforeInstantiation
第二次：SmartInstantiationAwareBeanPostProcessor—determineCandidateConstructors—由后置处理器决定返回那些构造方法
第三次：MergedBeanDefinitionPostProcessor——postProcessMergedBeanDefinition------缓存的
第四次：SmartInstantiationAwareBeanPostProcessor—getEarlyBeanReference----把对象放到Early当中--处理循环引用
第五次：InstantiationAwareBeanPostProcessor—postProcessAfterInstantiation---判断要不要填充属性
第六次：InstantiationAwareBeanPostProcessor—postProcessPropertyValues—处理属性的值
第七次：BeanPostProcessor—postProcessBeforeInitialization —处理AOP
第八次：BeanPostProcessor----postProcessAfterInitialization
第九次为销毁
那么到这里一个完整的springBean的初始化。
转载需标明出处 谢谢，体谅下原创，不容易。