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));
    }