Spring源码学习--Spring配置文件解析BeanDefinitionReader（二）

Spring配置文件的解析是通过BeanDefinitionReader来实现的，其实了解BeanDefinitionReader实现的机制就会发现，其只是将ApplicationContext.xml配置文件解析成Document对象，真正对xml中元素解析的类是在BeanDefinitionDocumentReader的实现类中来完成的，接下来我们也会对它进行介绍。

对ApplicationContext.xml中开始解析的方法是loadBeanDefinitions

AbstractBeanDefinitionReader的loadBeanDefinitions中会对ApplicationContext.xml进行解析

@Override
  public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
    Assert.notNull(locations, "Location array must not be null");
    int counter = 0;
    for (String location : locations) {
      counter += loadBeanDefinitions(location);
    }
    return counter;
  }

@Override
  public int loadBeanDefinitions(String location) throws BeanDefinitionStoreException {
    return loadBeanDefinitions(location, null);
  }

loadBeanDefinitions中会根据文件地址来进行解析操作：

public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {
    //判断资源地址类型
    if (resourceLoader instanceof ResourcePatternResolver) {
      // Resource pattern matching available.
      try {
        Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
        //在子类的loadBeanDefinitions进行解析操作
        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.
      Resource resource = resourceLoader.getResource(location);
      //在子类的loadBeanDefinitions进行解析操作
      int loadCount = loadBeanDefinitions(resource);
      if (actualResources != null) {
        actualResources.add(resource);
      }
      if (logger.isDebugEnabled()) {
        logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
      }
      return loadCount;
    }
  }

loadBeanDefinitions是在子类XmlBeanDefinitionReader中实现

@Override
  public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
    return loadBeanDefinitions(new EncodedResource(resource));
  }

doLoadBeanDefinitions会将文件地址解析为数据流，然后解析数据流

public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
    
    ..........
    
    try {
      //从xml文件中获取流
      InputStream inputStream = encodedResource.getResource().getInputStream();
      try {
        InputSource inputSource = new InputSource(inputStream);
        if (encodedResource.getEncoding() != null) {
          inputSource.setEncoding(encodedResource.getEncoding());
        }
        //解析文件流
        return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
      }
      finally {
        inputStream.close();
      }
    }
    .......
  }

doLoadBeanDefinitions中会将文件流解析成Document对象

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
      throws BeanDefinitionStoreException {
    try {
      Document doc = doLoadDocument(inputSource, resource);
      return registerBeanDefinitions(doc, resource);
    }
    .....
  }

registerBeanDefinitions中会创建BeanDefinitionDocumentReader来对Document进行解析，对Spring配置文件中的元素进行解析处理。

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
    //创建Document解析处理器
    BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
    int countBefore = getRegistry().getBeanDefinitionCount();
    //在BeanDefinitionDocumentReader中解析xml中配置的元素
    documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
    return getRegistry().getBeanDefinitionCount() - countBefore;
  }

总结：简单来说BeanDefinitionReader所做的处理操作是将配置的ApplicationContext.xml解析成为Document对象，接下来会有

BeanDefinitionDocumentReader来对Document进行解析。