一、问题剖析
1.spring容器的启动过程，启动期间都做了什么？什么时候创立单实例bean？
2.ioc是如何创立这些单实例bean，是如何治理的？保留在哪里？
二、Debug剖析
ClassPathXmlApplicationContext的继承树
1.创立spring容器，读取配置文件，类门路下加载配置文件
ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");2.最先加载的应该是动态初始化块，它会随着类的加载而加载
static {//在WebLogic 8.1中，在应用程序敞开时，紧急加载ContextCLosedEvent类以防止奇怪的类加载器问题。 ContextClosedEvent.class.getName();}3.调用ClassPathXmlApplicationContext的构造方法
/** * 创立一个新的classPathXmlApplicationcontext，从给定的XML文件加载定义，并主动刷新该ontext。 * @param applicationContext.xml * 如果上下文创立失败，@抛出BeansException */public ClassPathXmlApplicationContext(String configLocation) throws BeansException {//调用类中其余结构 this(new String[] {configLocation}, true, null);}4.参数解析
| 参数名 | 参数值 |
|---|---|
| String[] configLocations | qpplicationContext.xml |
| refresh | true |
| parent | null |
/** * 创立一个新的classPathXmlApplicationContextwith给定的父类，从给定的XML文件加载定义。 * @param configLocations 资源地位数组 * @param refresh 是否主动刷新上下文 * 加载所有bean定义并创立所有单例。或者，在进一步的configuri之后手动调用刷新康泰克斯的 * @param 父上下文后手动调用刷新 * 如果上下文创立失败，@抛出BeansException * @see #refresh() */public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent) throws BeansException { // 1.初始化父类 super(parent); // 2.设置本地的配置信息 setConfigLocations(configLocations); // 3.实现Spring容器的初始化 if (refresh) { //true 进入refresh办法 refresh(); //所有单实例创立实现 }}5.refresh()解析
synchronized (this.startupShutdownMonitor) { // 筹备此上下文以进行刷新 prepareRefresh(); // spring解析xml配置文件，将要创立的所有bean 的配置信息保存起来 ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();5.1 ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory()解析
5.1.1 obtainFreshBeanFactory();
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() { refreshBeanFactory(); //刷新beanFactory return getBeanFactory(); }5.1.2 refreshBeanFactory();
//对上下文的底层bean工厂执行一次理论刷新，敞开上一个bean工厂(如果有的话)和为上下文生命周期的下一阶段初始化afreshbean工厂。if (hasBeanFactory()) { //判断是否曾经创立beanFactory 如果存在beanFactory则销毁并敞开 destroyBeans(); closeBeanFactory();}try { DefaultListableBeanFactory beanFactory = createBeanFactory();//创立一个新的beanFactory beanFactory.setSerializationId(getId()); customizeBeanFactory(beanFactory); loadBeanDefinitions(beanFactory);//通过beanFactory加载beanDefinition synchronized (this.beanFactoryMonitor) { this.beanFactory = beanFactory;//对beanFactory进行从新赋值。 }}catch (IOException ex) { throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);}5.1.3 createBeanFactory()
protected DefaultListableBeanFactory createBeanFactory() {//传入这个context的父context外部的beanFactory return new DefaultListableBeanFactory(getInternalParentBeanFactory());//由此可见这个context外部的beanFacotry5.2 解析完xml后
// 筹备在此上下文中应用的bean工厂 prepareBeanFactory(beanFactory); try { // 容许在上下文子类中对bean工厂进行后处理 postProcessBeanFactory(beanFactory); // 调用上下文中注册为bean的工厂处理器 invokeBeanFactoryPostProcessors(beanFactory); // 注册拦挡bean创立的bean处理器 registerBeanPostProcessors(beanFactory); // 初始化消息来源,用来反对国际化性能 initMessageSource(); // 初始化多事件派发器 initApplicationEventMulticaster(); // 初始化特定上下文子类中的其余专门化bean，专门留给子类的办法 onRefresh(); // 查看侦听器bean并注册它们注册监听器 registerListeners(); // 实例化所有残余的(非提早-init)单例 finishBeanFactoryInitialization(beanFactory);5.3 finishBeanFactoryInitialization(beanFactory)实现单实例bean创立;
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) { // 初始化类型转换的组件服务 （次要用于自定义类型转化） 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)); } //如果没有bean前期解决 //(例如PropertyPlaceholderConfigurer bean)之前注册任何: //此时，次要用于解析正文属性值。 if (!beanFactory.hasEmbeddedValueResolver()) { beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal)); } // 初始化加载时的Autowire String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false); for (String weaverAwareName : weaverAwareNames) { getBean(weaverAwareName); } //停止使用长期类加载器进行类型匹配 beanFactory.setTempClassLoader(null); //容许缓存所有bean定义元数据，不冀望进一步更改 beanFactory.freezeConfiguration(); //实例化所有残余的(非提早-init)单单实例bean beanFactory.preInstantiateSingletons();}beanFactory.preInstantiateSingletons()解析
//日志记录 if (logger.isTraceEnabled()) { logger.trace("Pre-instantiating singletons in " + this); } //迭代一个正本以容许init办法注册新的bean定义。 //尽管这可能不是惯例工厂疏导程序的一部分，但它在其余方面工作得很好。 //beanDefinitionNames 所有定义bean的名字 List<String> beanNames = new ArrayList<>(this.beanDefinitionNames); // 按程序初始化所有非懒加载的单实例bean for (String beanName : beanNames) { //依据bean的id获取到bean的具体定义信息 RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName); //判断bean不是一个形象的、非懒加载的单实例bean，所有这是ioc中bean的默认个性 if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) { //如果该bean是工厂bean，实现了FactoryBean接口的bean，就进入判断 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); //因为我并没有应用工厂创立bean，所以来到这行 } } }getBean(beanName):bean创立的细节
@Override public Object getBean(String name) throws BeansException { //重写BeanFactory的办法 return doGetBean(name, null, null, false); //调用了doGetBean接口 }doGetBean(name, null, null, false)：bean创立的细节（重点）
参数
| 参数名 | 参数值 |
|---|---|
| name | bean对象名称 |
| requiredType | null |
| args | null |
| typeCheckOnly | false |
protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType, @Nullable final Object[] args, boolean typeCheckOnly) throws BeansException { //先拿到要创立的bean名称 final String beanName = transformedBeanName(name); Object bean; // 从曾经注册的单实例bean外面查看有没有这个bean Object sharedInstance = getSingleton(beanName); if (sharedInstance != null && args == null) { //缓存里有则走上面的代码 if (logger.isTraceEnabled()) { if (isSingletonCurrentlyInCreation(beanName)) { logger.trace("Returning eagerly cached instance of singleton bean '" + beanName + "' that is not fully initialized yet - a consequence of a circular reference"); } else { logger.trace("Returning cached instance of singleton bean '" + beanName + "'"); } } bean = getObjectForBeanInstance(sharedInstance, name, beanName, null); } else { //第一次创立bean是没有的，所有走到这 //如果咱们曾经创立了这个bean实例，则会失败:咱们假如在循环援用中。 if (isPrototypeCurrentlyInCreation(beanName)) { throw new BeanCurrentlyInCreationException(beanName); } //查看父工厂中是否存在bean定义。 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 if (requiredType != null) { // No args -> delegate to standard getBean method. return parentBeanFactory.getBean(nameToLookup, requiredType); } else { return (T) parentBeanFactory.getBean(nameToLookup); } } if (!typeCheckOnly) { //typeCheckOnly false //标记bean的状态为曾经被创立，为了避免多线程并发创立bean markBeanAsCreated(beanName); } try { //获取合并后的bean的定义信息 final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName); checkMergedBeanDefinition(mbd, beanName, args); //拿到以后bean创立之前所须要提前创立创立的bean，depends-on属性，调用依赖关系设置，如果有此属性就循环创立deponds-on属性依赖的bean 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); } } } // 如果是单例，创立bean if (mbd.isSingleton()) { // getSington办法里创立bean sharedInstance = getSingleton(beanName, () -> { try { //bean的创立次要办法 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); }getSingleton(beanName, () -> {} 细节
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) { Assert.notNull(beanName, "Bean name must not be null"); synchronized (this.singletonObjects) { //先从单实例对象中将这些beanget进去 Object singletonObject = this.singletonObjects.get(beanName); singletonObjects是一个hashMap
//依照对象的名字和对象实例缓存所有单实例beanprivate final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256); if (singletonObject == null) { //第一次创立为null。进入上面的办法 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 { //在这里利用了反射创立了单实例bean singletonObject = singletonFactory.getObject(); newSingleton = true; } catch (IllegalStateException ex) { //让单例对象同时隐式地呈现 //如果是，持续，因为异样表明状态。> 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) { //创立完单实例bean后调用此办法 addSingleton(beanName, singletonObject); addSingleton(beanName, singletonObject)细节
protected void addSingleton(String beanName, Object singletonObject) { synchronized (this.singletonObjects) { //singletonObjects 之前创立的map汇合，将bean对象退出到map中 //所以，创立好的对象最终会保留在这个map中 this.singletonObjects.put(beanName, singletonObject); this.singletonFactories.remove(beanName); this.earlySingletonObjects.remove(beanName); this.registeredSingletons.add(beanName); } } } } return singletonObject; }} 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.isTraceEnabled()) { logger.trace("Failed to convert bean '" + name + "' to required type '" + ClassUtils.getQualifiedName(requiredType) + "'", ex); } throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass()); } } return (T) bean; } // Trigger post-initialization callback for all applicable beans... 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(); } } }} // Last step: publish corresponding event. 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(); }}总结
最终单实例bean对象保留DefaultSingletonBeanRegistry类中的singletonObjects属性
private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256);