Dubbo源码学习ScopeBeanFactory对比Spring 的BeanFactory

Posted 2022-11-28 Dream_it_possible！

目录

1. ScopeBeanFactory与BeanFactory对比

2. 注册Bean

3. 执行一系列的PostProccessor

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1. ScopeBeanFactory与BeanFactory对比

        ScopeBeanFactory是Dubbo自己定义的管理Bean的一个类, 他可与ScopeModel一起实现应用和模块之间的数据共享等功能，ScopeBeanFactory在ScopeModel类的initialize()方法里初始化, scopeModel 有3个实现，分别为ApplilcationMode、FrameWorkModel和ModuleMode, 其中FrameWorkModel可实现多应用之间的共享数据功能。

public abstract class ScopeModel implements ExtensionAccessor 
    protected static final Logger LOGGER = LoggerFactory.getLogger(ScopeModel.class);
  
  protected void initialize() 
        this.extensionDirector = new ExtensionDirector(parent != null ? parent.getExtensionDirector() : null, scope, this);
        this.extensionDirector.addExtensionPostProcessor(new ScopeModelAwareExtensionProcessor(this));
        this.beanFactory = new ScopeBeanFactory(parent != null ? parent.getBeanFactory() : null, extensionDirector);
        this.destroyListeners = new LinkedList<>();
        this.classLoaderListeners = new LinkedList<>();
        this.attributes = new ConcurrentHashMap<>();
        this.classLoaders = new ConcurrentHashSet<>();

        // Add Framework's ClassLoader by default
        ClassLoader dubboClassLoader = ScopeModel.class.getClassLoader();
        if (dubboClassLoader != null) 
            this.addClassLoader(dubboClassLoader);
        
    
//...

        ScopeBeanFactory 管理Bean的方式类似于Spring  BeanFactory， 不同的是Spring BeanFactory是一个接口，主要实现是DefaultListableBeanFactory。 

        ScopeBeanFactory和Spring 的BeanFactory,对比如下:

	Dubbo	Spring	其他
描述Bean的方式	BeanInfo对象	BeanDefinition接口
有无父亲	包含parent, 在本类里定义。	包含parent , BeanFactory, 在AbstractBeanFactory抽象类里定义。	他们在getBean时都先找自己的，自己没有再找父亲的, 判断的时候如果自己没有，那么直接返回false, 因为父亲那儿也时基于儿子的。
存放容器	CopyOnWriteArrayList	ConcurrentHashMap
初始化Bean后的操作	执行initializeBean方法，然后执行所有的ExtensionPostProccess	Bean 初始化结束后在AbstractAutowireCapableBeanFactory类里applyBeanPostProceesorAfterInitialization(Object existingBean, String name)
PostProcessor	ExtensionAccessor接口提供了一系列的ExtensionPostProcessor	在AbstractAutowireCapableBeanFactory抽象类里通过一个CopyOnWriteArrayList存放了所有的BeanPostProccessor	注册Bean完成后执行
能限制Bean的作用域，跨应用共享	支持，通过选择不同的ScopeModel实现。	不支持

         由上，我感觉ScopeBeanFactory就是一个简化版的BeanFactory，接着跟着代码一探究竟。

2. 注册Bean

注册Bean， 通过name 和对象可以直接注册Bean。

    
    public void registerBean(Object bean) 
        this.registerBean(null, bean);
    

    public void registerBean(String name, Object bean) 
        checkDestroyed();
        // avoid duplicated register same bean
        if (containsBean(name, bean)) 
            return;
        

        Class<?> beanClass = bean.getClass();
        if (name == null) 
            name = beanClass.getName() + "#" + getNextId(beanClass);
        
        initializeBean(name, bean);

        registeredBeanInfos.add(new BeanInfo(name, bean));
    

        this.getOrRegisterBean, 如果没有Bean，那么根据class创建Bean

    public <T> T getOrRegisterBean(String name, Class<T> type) 
        T bean = getBean(name, type);
        if (bean == null) 
            // lock by type
            synchronized (type) 
                bean = getBean(name, type);
                if (bean == null) 
                    bean = createAndRegisterBean(name, type);
                
            
        
        return bean;
    

         也通过supplier传进来一个Bean, 执行apply 方法的时候回调。

    public <T> T getOrRegisterBean(Class<T> type, Function<? super Class<T>, ? extends T> mappingFunction) 
        return getOrRegisterBean(null, type, mappingFunction);
    

    public <T> T getOrRegisterBean(String name, Class<T> type, Function<? super Class<T>, ? extends T> mappingFunction) 
        T bean = getBean(name, type);
        if (bean == null) 
            // lock by type
            synchronized (type) 
                bean = getBean(name, type);
                if (bean == null) 
                    // 执行目标方法，得到bean对象。
                    bean = mappingFunction.apply(type);
                    registerBean(name, bean);
                
            
        
        return bean;
    

3. 执行一系列的PostProccessor

         注册Bean后的初始化，执行类似于Spring 的Bean的初始化动作:

        执行一系列的PostProcessor, Spring里叫BeanPostProcessor, 这里只是换了个名字叫ExtensionPostProcessor。

    private void initializeBean(String name, Object bean) 
        checkDestroyed();
        try 
            if (bean instanceof ExtensionAccessorAware) 
                ((ExtensionAccessorAware) bean).setExtensionAccessor(extensionAccessor);
            
            // 执行postProcessAfterInitialization(bean,name)， 执行一系列的BeanPostProccessor
            for (ExtensionPostProcessor processor : extensionPostProcessors) 
                processor.postProcessAfterInitialization(bean, name);
            
         catch (Exception e) 
            throw new ScopeBeanException("register bean failed! name=" + name + ", type=" + bean.getClass().getName(), e);
        
    

        Spring 会在初始化完毕后，AbstractAutowireCapableBeanFactory实现了执行一系列的BeanPostProcessor

    protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) 
        if (System.getSecurityManager() != null) 
            AccessController.doPrivileged(new PrivilegedAction<Object>() 
                public Object run() 
                    AbstractAutowireCapableBeanFactory.this.invokeAwareMethods(beanName, bean);
                    return null;
                
            , this.getAccessControlContext());
         else 
            this.invokeAwareMethods(beanName, bean);
        

        Object wrappedBean = bean;
        if (mbd == null || !mbd.isSynthetic()) 
            wrappedBean = this.applyBeanPostProcessorsBeforeInitialization(bean, beanName);
        

        try 
            this.invokeInitMethods(beanName, wrappedBean, mbd);
         catch (Throwable var6) 
            throw new BeanCreationException(mbd != null ? mbd.getResourceDescription() : null, beanName, "Invocation of init method failed", var6);
        

        // 执行postProceesorAfterInitialization
        if (mbd == null || !mbd.isSynthetic()) 
            wrappedBean = this.applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
        

        return wrappedBean;
    

        进入到 applyBeanPostProcessorsAfterInitialization方法: 

    public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName) throws BeansException 
        Object result = existingBean;
        Iterator i$ = this.getBeanPostProcessors().iterator();

        do 
            if (!i$.hasNext()) 
                return result;
            
            // 执行postProcessor
            BeanPostProcessor beanProcessor = (BeanPostProcessor)i$.next();
            result = beanProcessor.postProcessAfterInitialization(result, beanName);
         while(result != null);

        return result;
    

        看了代码后，我感觉Dubbo的ScopeBeanFactory的实现基本是借鉴于Spring 的BeanFactory的设计实现 ，更清晰明了啦。