`
ol_beta
  • 浏览: 289271 次
  • 性别: Icon_minigender_1
  • 来自: 天津
社区版块
存档分类
最新评论

Spring源码阅读——获得bean

阅读更多

已XmlWebApplicationContext为例,从getBean(String name)方法开始,读一下Spring是怎么通过名字获得bean的。

其他方式类似这个过程。

这个是XmlWebApplicationContext的类继承体系:



 首先,getBean(String name)是在BeanFactory接口中定义的,而在AbstractApplicationContext中实现:

public Object getBean(String name) throws BeansException {
		return getBeanFactory().getBean(name);
	}

AbstractApplicationContext获得BeanFactory代理,然后用代理获得bean。这个代理的实现的getBean(String name)是在AbstractBeanFactory中实现的:

public Object getBean(String name) throws BeansException {
		return doGetBean(name, null, null, false);
	} 

这里的doGenBean才是真正获得bean的地方,下面逐步分析这个方法:

protected <T> T doGetBean(
			final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
			throws BeansException {

		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 (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);
			}

			final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
			checkMergedBeanDefinition(mbd, beanName, args);

			// Guarantee initialization of beans that the current bean depends on.
			String[] dependsOn = mbd.getDependsOn();
			if (dependsOn != null) {
				for (String dependsOnBean : dependsOn) {
					getBean(dependsOnBean);
					registerDependentBean(dependsOnBean, beanName);
				}
			}

			// Create bean instance.
			if (mbd.isSingleton()) {
				sharedInstance = getSingleton(beanName, new ObjectFactory() {
					public Object getObject() throws BeansException {
						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 '" + scopeName + "'");
				}
				try {
					Object scopedInstance = scope.get(beanName, new ObjectFactory() {
						public Object getObject() throws BeansException {
							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);
				}
			}
		}

		// Check if required type matches the type of the actual bean instance.
		if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
			throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
		}
		return (T) bean;
	}

  首先从缓存查找单例:

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);
		}

如果能从缓存中获得已缓存的单例bean,并且参数args(只能在创建prototype时使用)为空,那么直接返回缓存中的bean,否则继续创建bean:

BeanFactory parentBeanFactory = getParentBeanFactory();
			if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
				// Not found -> check parent.
				String nameToLookup = originalBeanName(name);
				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);
				}
			}

如果能AbstractBeanFactory存在父级BeanFactory,并且当前AbstractBeanFactory不存在bean的定义(BeanDefinition),就把创建bean交给父级Beanfactory。

	BeanFactory parentBeanFactory = getParentBeanFactory();
			if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
				// Not found -> check parent.
				String nameToLookup = originalBeanName(name);
				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);
				}
			}

 如果父级BeanFactory不存在或者AbstractBeanFactory存在当前bean的定义,那就从BeanDefinition中创建bean。
在用BeanDefinition创建bean过程中首先要递归的解决依赖:

final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
			checkMergedBeanDefinition(mbd, beanName, args);

			// Guarantee initialization of beans that the current bean depends on.
			String[] dependsOn = mbd.getDependsOn();
			if (dependsOn != null) {
				for (String dependsOnBean : dependsOn) {
					getBean(dependsOnBean);
					registerDependentBean(dependsOnBean, beanName);
				}
			}

处理完依赖后,开始创建bean实例。如果bean是单例,则创建这个单例并放入缓存:

if (mbd.isSingleton()) {
				sharedInstance = getSingleton(beanName, new ObjectFactory() {
					public Object getObject() throws BeansException {
						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);
			}

 创建bean的实际动作是在createBean方法中,这个方法在AbstractAutowireCapableBeanFactory中实现:

protected Object createBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
			throws BeanCreationException {

		if (logger.isDebugEnabled()) {
			logger.debug("Creating instance of bean '" + beanName + "'");
		}
		// Make sure bean class is actually resolved at this point.
		resolveBeanClass(mbd, beanName);

		// Prepare method overrides.
		try {
			mbd.prepareMethodOverrides();
		}
		catch (BeanDefinitionValidationException ex) {
			throw new BeanDefinitionStoreException(mbd.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, mbd);
			if (bean != null) {
				return bean;
			}
		}
		catch (Throwable ex) {
			throw new BeanCreationException(mbd.getResourceDescription(), beanName,
					"BeanPostProcessor before instantiation of bean failed", ex);
		}

		Object beanInstance = doCreateBean(beanName, mbd, args);
		if (logger.isDebugEnabled()) {
			logger.debug("Finished creating instance of bean '" + beanName + "'");
		}
		return beanInstance;
	}

 createBean方法首先验证要创建bean的Class,然后准备要重写的方法。
接下来,将解析是否创建一个bean的代理而不是正在创建这个bean:

Object bean = resolveBeforeInstantiation(beanName, mbd);

在AbstractAutowireCapableBeanFactory是创建代理具体实现:

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.hasBeanClass() && !mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
				bean = applyBeanPostProcessorsBeforeInstantiation(mbd.getBeanClass(), beanName);
				if (bean != null) {
					bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
				}
			}
			mbd.beforeInstantiationResolved = (bean != null);
		}
		return bean;
	}

如果代理不为空,就返回代理;否则创建bean:

Object beanInstance = doCreateBean(beanName, mbd, args);

 创建过程是在AbstractAutowireCapableBeanFactory中实现的:

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {
		// Instantiate the bean.
		BeanWrapper instanceWrapper = null;
		if (mbd.isSingleton()) {
			instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
		}
		if (instanceWrapper == null) {
			instanceWrapper = createBeanInstance(beanName, mbd, args);
		}
		final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
		Class beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);

		// Allow post-processors to modify the merged bean definition.
		synchronized (mbd.postProcessingLock) {
			if (!mbd.postProcessed) {
				applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
				mbd.postProcessed = true;
			}
		}

		// Eagerly cache singletons to be able to resolve circular references
		// even when triggered by lifecycle interfaces like BeanFactoryAware.
		boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
				isSingletonCurrentlyInCreation(beanName));
		if (earlySingletonExposure) {
			if (logger.isDebugEnabled()) {
				logger.debug("Eagerly caching bean '" + beanName +
						"' to allow for resolving potential circular references");
			}
			addSingletonFactory(beanName, new ObjectFactory() {
				public Object getObject() throws BeansException {
					return getEarlyBeanReference(beanName, mbd, bean);
				}
			});
		}

		// Initialize the bean instance.
		Object exposedObject = bean;
		try {
			populateBean(beanName, mbd, instanceWrapper);
			if (exposedObject != null) {
				exposedObject = initializeBean(beanName, exposedObject, mbd);
			}
		}
		catch (Throwable ex) {
			if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
				throw (BeanCreationException) ex;
			}
			else {
				throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
			}
		}

		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<String>(dependentBeans.length);
					for (String dependentBean : dependentBeans) {
						if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
							actualDependentBeans.add(dependentBean);
						}
					}
					if (!actualDependentBeans.isEmpty()) {
						throw new BeanCurrentlyInCreationException(beanName,
								"Bean with name '" + beanName + "' has been injected into other beans [" +
								StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
								"] in its raw version as part of a circular reference, but has eventually been " +
								"wrapped. This means that said other beans do not use the final version of the " +
								"bean. This is often the result of over-eager type matching - consider using " +
								"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
					}
				}
			}
		}

		// Register bean as disposable.
		try {
			registerDisposableBeanIfNecessary(beanName, bean, mbd);
		}
		catch (BeanDefinitionValidationException ex) {
			throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
		}

		return exposedObject;
	} 

doCreateBean方法主要填充bean的属性,处理依赖关系,处理post-processors,然后生成Constructor,根据测试采用jdk的反射或者CGLIB(默认)生成bean,关于这个过程,有时间再详细说,先欠着吧,这个编辑器太不好用了,真的写写不下去了...

 

  • 大小: 35.9 KB
分享到:
评论

相关推荐

    二、Spring源码分析——BeanFactory

    《Spring源码分析——BeanFactory》 在Java的IoC(Inversion of Control)和DI(Dependency Injection)领域,Spring框架扮演着至关重要的角色。BeanFactory是Spring的核心组件之一,它是容器的基石,负责管理应用...

    spring源码阅读——1.spring-core-3.2.9

    阅读Spring Core的源码可以帮助我们更深入地理解其工作原理,提高解决问题的能力。通过分析`readme.txt`,我们可以获得关于这个版本的更多细节,例如新特性、已知问题和改进之处。同时,了解XML配置文件的结构和作用...

    三、Spring源码分析——ApplicationContext

    《Spring源码分析——ApplicationContext》 在Java世界中,Spring框架是不可或缺的一部分,它以其强大的IoC(Inversion of Control,控制反转)和AOP(Aspect Oriented Programming,面向切面编程)特性,极大地...

    四、Spring源码分析——动态代理

    分析Spring源码有助于深入理解其动态代理的工作原理。例如,可以查看`org.springframework.aop.framework.JdkDynamicAopProxy`和`org.springframework.aop.framework.CglibAopProxy`这两个类,它们分别实现了JDK和...

    【框架源码篇 04】Spring源码手写篇-Bean定义配置化

    在本篇【框架源码篇 04】中,我们将深入探讨Spring框架的核心概念——Bean定义配置化。Spring是Java领域最广泛使用的依赖注入(Dependency Injection,简称DI)和面向切面编程(Aspect-Oriented Programming,简称...

    Spring源码解析.zip

    本压缩包“Spring源码解析”提供了对Spring框架核心组件——IOC(Inversion of Control,控制反转)、AOP(Aspect Oriented Programming,面向切面编程)以及Transaction(事务管理)的源码分析,帮助开发者更全面地...

    spring 源码中文注释

    在源码分析的过程中,读者会深入理解Spring的内部工作机制,例如如何解析配置、如何创建bean实例、如何实现AOP代理等。这将有助于开发者编写更高效、更健壮的代码,也能为参与Spring的扩展或定制打下坚实基础。 总...

    京东T5级大牛带你解读Spring核心源码——1小时手写SpringMVC~

    ### Spring核心源码解读与手动实现SpringMVC #### 一、Spring框架简介 Spring框架是由Rod Johnson在2004年发起的一个开源项目,它是一个轻量级的控制反转(IoC)和面向切面(AOP)的容器。Spring框架的核心特性包括:...

    Spring源码解析.pdf

    ### Spring源码解析知识点 #### 一、Spring IoC 容器详解 ##### 1. BeanFactory —— 最基础的IoC容器 - **概念**:`BeanFactory` 是Spring框架中最基本的IoC容器,它负责管理Bean的生命周期,包括创建、配置和...

    4Spring自动装配——annotation resource方式

    在Spring框架中,自动装配(Auto-Wiring)是一种简化依赖注入(Dependency Injection,DI)配置的方式,它允许...通过阅读和理解源码,我们可以更好地掌握Spring自动装配的工作原理,从而更好地利用这一强大的功能。

    Spring5 源码分析(第 2 版)-某Tom老师

    《Spring5 源码分析(第 2 版)》是某Tom老师精心编写的深度解析文档,旨在帮助读者全面理解Spring5的核心机制和设计理念。Spring作为Java领域最为广泛应用的框架之一,其源码的深入理解对于开发者来说至关重要。这篇...

    SpringBoot源码解析——BeanDefinitionLoader 源码分析.docx

    在源码分析中,我们首先看到`prepareContext`方法被调用,这是`SpringApplication`类中的一个重要方法,它负责初始化`ApplicationContext`(应用上下文)并为后续的bean加载做准备。 `prepareContext`方法做了以下...

    Spring 源码分析文档----自用

    ### Spring 源码分析——设计模式篇 #### 一、引言 Spring框架作为Java企业级开发领域中不可或缺的一部分,其内部集成了多种设计模式,不仅有助于提高系统的可维护性和扩展性,还能够帮助开发者更好地理解和应用...

    Spring学习笔记(9)----让Spring自动扫描和管理Bean

    在Spring框架中,自动扫描和管理Bean是一种便捷的方式,它允许开发者无需显式配置每个Bean,而是通过指定包路径来让Spring自动发现和管理Bean。本文将深入探讨这个主题,帮助你更好地理解和应用这一功能。 首先,让...

    spring源码

    这两部分源码揭示了Spring如何解析这些配置,创建bean实例,并管理它们之间的依赖关系。 总的来说,这个压缩包中的源码为深入理解Spring的AOP和IOC提供了宝贵的资源。通过对这些源码的学习,开发者不仅可以了解到...

    spring源码解析和mybatis学习

    本文将深入探讨这两个技术,并基于提供的资源——"Spring源码深度解析.pdf"和"MyBatis3用户指南中文版.pdf",对它们进行详细的知识点解析。 首先,让我们来了解Spring框架。Spring是一个开源的Java平台,它简化了...

    spring源码UML图

    首先,"spring源码UML图"通常包括以下几种类型的UML图: 1. 类图(Class Diagram):类图展示了Spring框架中的类和接口,以及它们之间的关系,如继承、实现、关联和依赖。这有助于我们了解Spring的核心组件,如...

    小读spring ioc源码(一)——整体介绍

    《Spring IOC源码解析(一)——整体介绍》 在深入理解Spring框架的过程中,源码分析是不可或缺的一环。本文将对Spring的IOC(Inversion of Control,控制反转)...希望本文能为你开启Spring源码探索之旅的第一步。

    Spring源码分析_Spring_IOC

    ### Spring源码分析_Spring_IOC:深入理解Spring的IOC容器机制 #### 基本概念与核心作用 在探讨Spring框架的核心组件之一——IOC(Inversion of Control,控制反转)容器之前,首先需要理解它在Spring框架中的角色...

    spring源码可导入eclipse版本 第五部分

    在本资源中,我们提供了可以直接导入Eclipse的Spring源码的第五部分,版本为4.3.18。这一版本的Spring包含了众多改进和修复,对于理解Spring的工作原理以及进行自定义开发非常有帮助。 首先,让我们深入了解一下...

Global site tag (gtag.js) - Google Analytics