4.2 spring-import 标签的解析;

　　对于spring配置文件的编写，我想，对于经历过庞大项目的人，都有那种恐惧的心理，太多的配置文件。不过，分模块都是大多数人能想到的方法，但是，怎么分模块，那就是仁者见仁，智者见智了。我的策略是使用import。
基本代码格式如下
 web.xml

<?xml version="1.0" encoding="gb2312"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">
<beans>

    <import resource="CTIContext.xml" />
    <import resource="customerContext.xml" />
    <import resource="customerServingContext.xml" />
    <import resource="manageContext.xml" />
    <import resource="routineContext.xml" />
    <import resource="systemContext.xml" />
</beans>

　　applicationContext.xml文件中使用import的方式导入有模块配置文件，以后若有新模块的加入，那就可以简单修改这个文件了,这样大大的简化了配置文件后期的复杂程度;

　　Spring 的解析代码如下;

 /**
      * Parse an "import" element and load the bean definitions from the given resource
      * into the bean factory.
      */
     protected void importBeanDefinitionResource(Element ele) {
         // 获取resource 属性
         String location = ele.getAttribute(RESOURCE_ATTRIBUTE);
         // 如果不存在resource ,则不做任何处理
         if (!StringUtils.hasText(location)) {
             getReaderContext().error("Resource location must not be empty", ele);
             return;
         }

         // Resolve system properties: e.g. "${user.dir}"
         // 解析系统属性.格式如 : ${user.dir}
         location = environment.resolveRequiredPlaceholders(location);

         Set<Resource> actualResources = new LinkedHashSet<Resource>(4);

         // Discover whether the location is an absolute or relative URI
         // 判断是绝对地址还是相对地址
         boolean absoluteLocation = false;
         try {
             absoluteLocation = ResourcePatternUtils.isUrl(location)
                     || ResourceUtils.toURI(location).isAbsolute();
         }
         catch (URISyntaxException ex) {
             // cannot convert to an URI, considering the location relative
             // unless it is the well-known Spring prefix "classpath*:"
         }

         // Absolute or relative?
         // 如果是绝对地址,则直接根据地址加载对应的配置文件
         if (absoluteLocation) {
             try {
                 int importCount = getReaderContext().getReader().loadBeanDefinitions(
                         location, actualResources);
                 if (logger.isDebugEnabled()) {
                     logger.debug("Imported " + importCount
                             + " bean definitions from URL location [" + location + "]");
                 }
             }
             catch (BeanDefinitionStoreException ex) {
                 getReaderContext().error(
                         "Failed to import bean definitions from URL location ["
                                 + location + "]", ele, ex);
             }
         }
         else {
             // No URL -> considering resource location as relative to the current file.
             // 如果是相对地址,则计算出绝对地址
             try {
                 int importCount;
                 // Resource 的多个子类 ,如 VfsResource,FileSystemResource,ClassPathResource
                 // 而每个Resource的createRelative 方法都不太一样所以这里先使用子类的方法尝试解析,
                 Resource relativeResource = getReaderContext().getResource().createRelative(
                         location);
                 if (relativeResource.exists()) {
                     importCount = getReaderContext().getReader().loadBeanDefinitions(
                             relativeResource);
                     actualResources.add(relativeResource);
                 }
                 else {
                     // 如果解析不成功,则使用默认解析器ResourcePatternResolver 进行解析
                     String baseLocation = getReaderContext().getResource().getURL().toString();
                     importCount = getReaderContext().getReader().loadBeanDefinitions(
                             StringUtils.applyRelativePath(baseLocation, location),
                             actualResources);
                 }
                 if (logger.isDebugEnabled()) {
                     logger.debug("Imported " + importCount
                             + " bean definitions from relative location [" + location
                             + "]");
                 }
             }
             catch (IOException ex) {
                 getReaderContext().error("Failed to resolve current resource location",
                         ele, ex);
             }
             catch (BeanDefinitionStoreException ex) {
                 getReaderContext().error(
                         "Failed to import bean definitions from relative location ["
                                 + location + "]", ele, ex);
             }
         }
         // 解析后进行监听器激活处理
         Resource[] actResArray = actualResources.toArray(new Resource[actualResources.size()]);
         getReaderContext().fireImportProcessed(location, actResArray, extractSource(ele));
     }