概念

BeanDefinition的存在形式有很多种，例如文件系统中的Bean定义文件或类路径中的Bean定义文件。这就意味需要不同的寻址方式在找到这些Bean定义文件。Resource定位指的是BeanDefinition的资源定位，就是找到这些Bean定义文件，并将这些信息抽象为统一的Resource对象，方便后面载入。

分析定位过程

以编程的方式使用DefaultListableBeanFactory时，我们会手动定义一个Resource来定位容器使用BeanDefinition：ClassPathResource res = new ``ClassPathResource("bean.xml");然后定义一个特定的读取器来读取这个资源，因为DefaultListableBeanFactory是一个纯粹的IoC容器，并没有自带帮我们定位资源和读取资源的功能，所以需要手动为其配置特定的读取器。所以这里就能看出使用ApplicationContext的优势所在，因为在ApplicationCo-ntext中，已经为我们提供了一系列加载不同Resource的读取器的实现，例如FileSystemXmlApplicationContext，ClassPathXmlApplicationContext以及XmlWebApplicationContext等，简单地从这些类的名字上分析，可以清楚地看到它们可以提供哪些不同的Resource读入功能。当然，使用DefaultListable-BeanFactory这种更底层的容器，能提高定制IoC容器的灵活性。下面分析FileSystemXmlApplicationContext的资源定位过程。

在上面的分析中，我们可以了解到FileSystemXmlApplicationContext的基本功能都在其基类中完成，它只是在构造函数中调用基类的refresh()来实例化容器和定义getResourceByPath()来定位BeanDefinition资源。所以可以知到getResourceByPath()是该容器定位资源调用的最后的方法，查看该方法的调用栈，便可了解整个定位过程。

分析调用栈：

• FileSystemXmlApplicationContext构造器中的refresh()方法是开始容器初始化的入口方法，由refresh()来启动整个调用。
• 在FileSystemXmlApplicationContext的基类AbstractRefreshableApplicationContext中的refreshBeanFactory()进行容器的初始化。从这里可知实际使用的BeanFactory是DefaultListableBeanFactory。代码如下：

/**     * This implementation performs an actual refresh of this context's underlying     * bean factory, shutting down the previous bean factory (if any) and     * initializing a fresh bean factory for the next phase of the context's lifecycle.     */    @Override    protected final void refreshBeanFactory() throws BeansException {    //这里判断如果已经建立了BeanFactory，则销毁并关闭该BeanFactory        if (hasBeanFactory()) {            destroyBeans();            closeBeanFactory();        }    /**      *创建实际存储BeanDefinition的DefaultListableBeanFactory，      *并调用loadBeanDefinitions(beanFactory)载入BeanDefinition信息      */         try {            DefaultListableBeanFactory beanFactory = createBeanFactory();            beanFactory.setSerializationId(getId());            customizeBeanFactory(beanFactory);            loadBeanDefinitions(beanFactory);            synchronized (this.beanFactoryMonitor) {                this.beanFactory = beanFactory;            }        }        catch (IOException ex) {            throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);        }    }  protected DefaultListableBeanFactory createBeanFactory() {        return new DefaultListableBeanFactory(getInternalParentBeanFactory());    }

• loadBeanDefinitions(DefaultListableBeanFactory beanFactory)，这个方法在基类AbstractRefreshableApp-licationContext中定义为抽象函数，因为允许有不同的载入方式，这里通过一个抽象函数把具体实现委托给子类，见图一和图二。FileSystemXmlApplicationContext是用xml方式读取的，所以基类AbstractXmlApplication-Context实现了这个方法。在这个方法中将DefaultListableBeanFactory绑定给BeanDefinitionReader，用于后续定位、载入和注册的回调。还需要注意的是beanDefinitionReader.setResourceLoader(this)这个方法，ResourceLoader的主要功能是用来定位和获取Resource对象的，而在Spring中每个ApplicationContext都是DefaultResourceLoader的子类(见图四)，所以FileSystemXmlApplicationContext中的getResourceByPath(S-tring path)是重写父类的方法。BeanDefinitionReader绑定完需要后续回调的组件后，就由BeanDefinitionR-eader继续后续处理，见图三。

   java /** * Load bean definitions into the given bean factory, typically through * delegating to one or more bean definition readers. * @param beanFactory the bean factory to load bean definitions into * @throws BeansException if parsing of the bean definitions failed * @throws IOException if loading of bean definition files failed * @see org.springframework.beans.factory.support.PropertiesBeanDefinitionReader * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader */ //AbstractRefreshableApplicationContext中的抽象方法。 protected abstract void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException;
  

  /**   * Loads the bean definitions via an XmlBeanDefinitionReader.   * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader   * @see #initBeanDefinitionReader   * @see #loadBeanDefinitions   */  @Override  protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {      // Create a new XmlBeanDefinitionReader for the given BeanFactory.      XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);      // Configure the bean definition reader with this context's      // resource loading environment.      beanDefinitionReader.setEnvironment(this.getEnvironment());      beanDefinitionReader.setResourceLoader(this);      beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));      // Allow a subclass to provide custom initialization of the reader,      // then proceed with actually loading the bean definitions.      initBeanDefinitionReader(beanDefinitionReader);      loadBeanDefinitions(beanDefinitionReader);  }

  

• loadBeanDefinitions(XmlBeanDefinitionReader reader)方法：对配置文件路径进行判断，如果路径不为空，则根据路径进行定位。

/**     * Load the bean definitions with the given XmlBeanDefinitionReader.     * 
The lifecycle of the bean factory is handled by the {@link #refreshBeanFactory}     * method; hence this method is just supposed to load and/or register bean definitions.     * @param reader the XmlBeanDefinitionReader to use     * @throws BeansException in case of bean registration errors     * @throws IOException if the required XML document isn't found     * @see #refreshBeanFactory     * @see #getConfigLocations     * @see #getResources     * @see #getResourcePatternResolver     */    protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {        Resource[] configResources = getConfigResources();        //对configResources进行载入解析和注册    if (configResources != null) {            reader.loadBeanDefinitions(configResources);        }        String[] configLocations = getConfigLocations();    //根据configLocations定位Resource        if (configLocations != null) {            reader.loadBeanDefinitions(configLocations);        }    }

• loadBeanDefinitions(String location, Set actualResources)方法：根据路径定位。

/**     * Load bean definitions from the specified resource location.     * 
The location can also be a location pattern, provided that the     * ResourceLoader of this bean definition reader is a ResourcePatternResolver.     * @param location the resource location, to be loaded with the ResourceLoader     * (or ResourcePatternResolver) of this bean definition reader     * @param actualResources a Set to be filled with the actual Resource objects     * that have been resolved during the loading process. May be null     * to indicate that the caller is not interested in those Resource objects.     * @return the number of bean definitions found     * @throws BeanDefinitionStoreException in case of loading or parsing errors     * @see #getResourceLoader()     * @see #loadBeanDefinitions(org.springframework.core.io.Resource)     * @see #loadBeanDefinitions(org.springframework.core.io.Resource[])     */    public int loadBeanDefinitions(String location, Set
     
       actualResources) throws BeanDefinitionStoreException {        //这里取得ResourceLoader，就是之前绑定的FileSystemXmlApplicationContext    ResourceLoader resourceLoader = getResourceLoader();        if (resourceLoader == null) {            throw new BeanDefinitionStoreException(                    "Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");        }    //这里对Resource的路径模式进行解析。        if (resourceLoader instanceof ResourcePatternResolver) {            // Resource pattern matching available.            try {        //调用DefaultResourceLoader的getResource完成具体的Resource定位                Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);                int loadCount = loadBeanDefinitions(resources);                if (actualResources != null) {                    for (Resource resource : resources) {                        actualResources.add(resource);                    }                }                if (logger.isDebugEnabled()) {                    logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");                }                return loadCount;            }            catch (IOException ex) {                throw new BeanDefinitionStoreException(                        "Could not resolve bean definition resource pattern [" + location + "]", ex);            }        }        else {            // Can only load single resources by absolute URL.      //调用DefaultResourceLoader的getResource完成具体的Resource定位            Resource resource = resourceLoader.getResource(location);            int loadCount = loadBeanDefinitions(resource);            if (actualResources != null) {                actualResources.add(resource);            }            if (logger.isDebugEnabled()) {                logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");            }            return loadCount;        }    }
     

• getResource(String location)方法：DefaultResourceLoader具体的Resource定位方法。

public Resource getResource(String location) {        Assert.notNull(location, "Location must not be null");  //这里处理带有classpath标识的Resource        if (location.startsWith(CLASSPATH_URL_PREFIX)) {            return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()), getClassLoader());        }        else {            try {                // Try to parse the location as a URL...        //这里出URL标识的Resource定位                URL url = new URL(location);                return new UrlResource(url);            }            catch (MalformedURLException ex) {                // No URL -> resolve as resource path.        //如果既不是classpath.也不是URL标识的Resource定位，则把getResource的        //重任交给getResourceByPath，这个方法是一个protected方法.默认的实现是得到        //一个ClassPathContextResource，这个方法常常会用子类来实现                return getResourceByPath(location);            }        }    }    //getResourceByPath的默认实现  protected Resource getResourceByPath(String path) {        return new ClassPathContextResource(path, getClassLoader());    }

• 上述代码的getResourceByPath(location);在这里就调用子类FileSystemXmlApplicationContext的该方法。