//AbstractBeanFactory.java @Override public Object getBean(String name) throws BeansException { return doGetBean(name, null, null, false); }复制代码
实际调用的是 AbstractBeanFactory#doGetBean(String name, Class<T> requiredType,Object[] args, boolean typeCheckOnly) 方法,该方法接受四个参数:java
//AbstractBeanFactory.java protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType, @Nullable final Object[] args, boolean typeCheckOnly) throws BeansException { //<1> 返回 bean 名称,剥离工厂引用前缀。 // 若是 name 是 alias ,则获取对应映射的 beanName 。 final String beanName = transformedBeanName(name); Object bean; // 从缓存中或者实例工厂中获取 Bean 对象 Object sharedInstance = getSingleton(beanName); if (sharedInstance != null && args == null) { 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 + "'"); } } // <2> 完成 FactoryBean 的相关处理,并用来获取 FactoryBean 的处理结果 bean = getObjectForBeanInstance(sharedInstance, name, beanName, null); } else { // <3> 由于 Spring 只解决单例模式下得循环依赖,在原型模式下若是存在循环依赖则会抛出异常。 if (isPrototypeCurrentlyInCreation(beanName)) { throw new BeanCurrentlyInCreationException(beanName); } // <4> 若是当前容器中没有找到,则从父类容器中加载 BeanFactory parentBeanFactory = getParentBeanFactory(); if (parentBeanFactory != null && !containsBeanDefinition(beanName)) { String nameToLookup = originalBeanName(name); // 若是,父类容器为 AbstractBeanFactory ,直接递归查找 if (parentBeanFactory instanceof AbstractBeanFactory) { return ((AbstractBeanFactory)parentBeanFactory).doGetBean(nameToLookup, requiredType, args, typeCheckOnly); // 用明确的 args 从 parentBeanFactory 中,获取 Bean 对象 } else if (args != null) { return (T)parentBeanFactory.getBean(nameToLookup, args); // 用明确的 requiredType 从 parentBeanFactory 中,获取 Bean 对象 } else if (requiredType != null) { return parentBeanFactory.getBean(nameToLookup, requiredType); // 直接使用 nameToLookup 从 parentBeanFactory 获取 Bean 对象 } else { return (T)parentBeanFactory.getBean(nameToLookup); } } // <5> 若是不是仅仅作类型检查则是建立bean,这里须要记录 if (!typeCheckOnly) { markBeanAsCreated(beanName); } try { // <6> 从容器中获取 beanName 相应的 GenericBeanDefinition 对象,并将其转换为 RootBeanDefinition 对象 final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName); // 检查给定的合并的 BeanDefinition checkMergedBeanDefinition(mbd, beanName, args); // <7> 处理所依赖的 bean String[] dependsOn = mbd.getDependsOn(); if (dependsOn != null) { for (String dep : dependsOn) { // 若给定的依赖 bean 已经注册为依赖给定的 bean // 即循环依赖的状况,抛出 BeanCreationException 异常 if (isDependent(beanName, dep)) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Circular depends-on relationship between '" + beanName + "' and '" + dep + "'"); } // 缓存依赖调用 TODO 芋艿 registerDependentBean(dep, beanName); try { // 递归处理依赖 Bean getBean(dep); } catch (NoSuchBeanDefinitionException ex) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "'" + beanName + "' depends on missing bean '" + dep + "'", ex); } } } // <8> bean 实例化 if (mbd.isSingleton()) { // 单例模式 sharedInstance = getSingleton(beanName, () -> { try { return createBean(beanName, mbd, args); } catch (BeansException ex) { // 显式从单例缓存中删除 Bean 实例 // 由于单例模式下为了解决循环依赖,可能他已经存在了,因此销毁它。 TODO 芋艿 destroySingleton(beanName); throw ex; } }); bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd); } else if (mbd.isPrototype()) { // 原型模式 Object prototypeInstance; try { beforePrototypeCreation(beanName); prototypeInstance = createBean(beanName, mbd, args); } finally { afterPrototypeCreation(beanName); } bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd); } else { // 得到 scopeName 对应的 Scope 对象 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 { // 从指定的 scope 下建立 bean Object scopedInstance = scope.get(beanName, () -> { // 加载前置处理 beforePrototypeCreation(beanName); try { // 建立 Bean 对象 return createBean(beanName, mbd, args); } finally { // 加载后缀处理 afterPrototypeCreation(beanName); } }); // 从 Bean 实例中获取对象 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; } } // <9> 检查须要的类型是否符合 bean 的实际类型 if (requiredType != null && !requiredType.isInstance(bean)) { try { // 执行转换 T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType); // 转换失败,抛出 BeanNotOfRequiredTypeException 异常 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; }复制代码
这段代码很是长,并且逻辑超复杂,咱们将拆解这段代码进行分析缓存
对应代码段以下:markdown
//AbstractBeanFactory.java final String beanName = transformedBeanName(name);复制代码
这里的 name 不必定是 beanName,多是 aliasName,也有多是 FactoryBean,因此这里须要调用 AbstractBeanFactory#transformedBeanName(String name) 方法,对 name 进行转换。代码段以下:ide
//AbstractBeanFactory.java protected String transformedBeanName(String name) { return canonicalName(BeanFactoryUtils.transformedBeanName(name)); }复制代码
//BeanFactoryUtils.java //缓存已经转换好的 name to beanName private static final Map<String, String> transformedBeanNameCache = new ConcurrentHashMap<>(); public static String transformedBeanName(String name) { Assert.notNull(name, "'name' must not be null"); if (!name.startsWith(BeanFactory.FACTORY_BEAN_PREFIX)) { return name; } // name = "&userService" // beanName = "userService" return transformedBeanNameCache.computeIfAbsent(name, beanName -> { do { beanName = beanName.substring(BeanFactory.FACTORY_BEAN_PREFIX.length()); } while (beanName.startsWith(BeanFactory.FACTORY_BEAN_PREFIX)); return beanName; }); }复制代码
//SimpleAliasRegistry.java //缓存 alias to beanName private final Map<String, String> aliasMap = new ConcurrentHashMap<>(16); public String canonicalName(String name) { String canonicalName = name; String resolvedName; // 循环,从 aliasMap 中,获取到最终映射的 beanName do { resolvedName = this.aliasMap.get(canonicalName); if (resolvedName != null) { canonicalName = resolvedName; } } while (resolvedName != null); return canonicalName; } 复制代码
对应代码段以下:post
//AbstractBeanFactory.java //从缓存或实例工厂中获取 Bean 对象 Object sharedInstance = getSingleton(beanName); if (sharedInstance != null && args == null) { 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 + "'"); } } // <x> 完成 FactoryBean 的相关处理,并用来获取 FactoryBean 的处理结果 bean = getObjectForBeanInstance(sharedInstance, name, beanName, null); }复制代码
详细解析,见 《【Spring 源码】—— IoC 之加载 Bean:从单例缓存中获取单》ui
对应代码段以下:this
//AbstractBeanFactory.java //Spring 只处理单列模式下的循环依赖 if (isPrototypeCurrentlyInCreation(beanName)) { throw new BeanCurrentlyInCreationException(beanName); }复制代码
Spring 只处理单例模式下得循环依赖,对于原型模式的循环依赖直接抛出异常。主要缘由仍是在于,和 Spring 解决循环依赖的策略有关。
spa
详细解析,见 《【Spring 源码】—— IoC 之加载 Bean:parentBeanFactory 与依赖处理》
prototype
对应代码段以下:
code
// AbstractBeanFactory.java // 若是当前容器中没有找到,则从父类容器中加载 BeanFactory parentBeanFactory = getParentBeanFactory(); if (parentBeanFactory != null && !containsBeanDefinition(beanName)) { String nameToLookup = originalBeanName(name); // 若是,父类容器为 AbstractBeanFactory ,直接递归查找 if (parentBeanFactory instanceof AbstractBeanFactory) { return ((AbstractBeanFactory)parentBeanFactory).doGetBean(nameToLookup, requiredType, args, typeCheckOnly); // 用明确的 args 从 parentBeanFactory 中,获取 Bean 对象 } else if (args != null) { return (T)parentBeanFactory.getBean(nameToLookup, args); // 用明确的 requiredType 从 parentBeanFactory 中,获取 Bean 对象 } else if (requiredType != null) { return parentBeanFactory.getBean(nameToLookup, requiredType); // 直接使用 nameToLookup 从 parentBeanFactory 获取 Bean 对象 } else { return (T)parentBeanFactory.getBean(nameToLookup); } }复制代码
若是当前容器中没有相对应的 BeanDefinition 对象,则会尝试从父容器中加载,而后递归调用 getBean(...) 方法。
详细解析,见 《【Spring 源码】—— IoC 之加载 Bean:parentBeanFactory 与依赖处理》
对应代码段以下:
// AbstractBeanFactory.java // 若是不是仅仅作类型检查则是建立bean,这里须要记录 if (!typeCheckOnly) { markBeanAsCreated(beanName); }复制代码
详细解析,见 《【Spring 源码】—— IoC 之加载 Bean:parentBeanFactory 与依赖处理》
对应代码段以下:
// AbstractBeanFactory.java // 从容器中获取 beanName 相应的 GenericBeanDefinition 对象,并将其转换为 RootBeanDefinition 对象 final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName); // 检查给定的合并的 BeanDefinition checkMergedBeanDefinition(mbd, beanName, args);复制代码
..todo