4.2 spring-import 标签的解析;

浏览数：44 / 时间：2015年06月08日

　　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;

 1 /**
 2      * Parse an "import" element and load the bean definitions from the given resource
 3      * into the bean factory.
 4      */
 5     protected void importBeanDefinitionResource(Element ele) {
 6         // 获取resource 属性
 7         String location = ele.getAttribute(RESOURCE_ATTRIBUTE);
 8         // 如果不存在resource ,则不做任何处理
 9         if (!StringUtils.hasText(location)) {
10             getReaderContext().error("Resource location must not be empty", ele);
11             return;
12         }
13 
14         // Resolve system properties: e.g. "${user.dir}"
15         // 解析系统属性.格式如 : ${user.dir}
16         location = environment.resolveRequiredPlaceholders(location);
17 
18         Set<Resource> actualResources = new LinkedHashSet<Resource>(4);
19 
20         // Discover whether the location is an absolute or relative URI
21         // 判断是绝对地址还是相对地址
22         boolean absoluteLocation = false;
23         try {
24             absoluteLocation = ResourcePatternUtils.isUrl(location)
25                     || ResourceUtils.toURI(location).isAbsolute();
26         }
27         catch (URISyntaxException ex) {
28             // cannot convert to an URI, considering the location relative
29             // unless it is the well-known Spring prefix "classpath*:"
30         }
31 
32         // Absolute or relative?
33         // 如果是绝对地址,则直接根据地址加载对应的配置文件
34         if (absoluteLocation) {
35             try {
36                 int importCount = getReaderContext().getReader().loadBeanDefinitions(
37                         location, actualResources);
38                 if (logger.isDebugEnabled()) {
39                     logger.debug("Imported " + importCount
40                             + " bean definitions from URL location [" + location + "]");
41                 }
42             }
43             catch (BeanDefinitionStoreException ex) {
44                 getReaderContext().error(
45                         "Failed to import bean definitions from URL location ["
46                                 + location + "]", ele, ex);
47             }
48         }
49         else {
50             // No URL -> considering resource location as relative to the current file.
51             // 如果是相对地址,则计算出绝对地址
52             try {
53                 int importCount;
54                 // Resource 的多个子类 ,如 VfsResource,FileSystemResource,ClassPathResource
55                 // 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,
56                 Resource relativeResource = getReaderContext().getResource().createRelative(
57                         location);
58                 if (relativeResource.exists()) {
59                     importCount = getReaderContext().getReader().loadBeanDefinitions(
60                             relativeResource);
61                     actualResources.add(relativeResource);
62                 }
63                 else {
64                     // 如果解析不成功,则使用默认解析器ResourcePatternResolver 进行解析
65                     String baseLocation = getReaderContext().getResource().getURL().toString();
66                     importCount = getReaderContext().getReader().loadBeanDefinitions(
67                             StringUtils.applyRelativePath(baseLocation, location),
68                             actualResources);
69                 }
70                 if (logger.isDebugEnabled()) {
71                     logger.debug("Imported " + importCount
72                             + " bean definitions from relative location [" + location
73                             + "]");
74                 }
75             }
76             catch (IOException ex) {
77                 getReaderContext().error("Failed to resolve current resource location",
78                         ele, ex);
79             }
80             catch (BeanDefinitionStoreException ex) {
81                 getReaderContext().error(
82                         "Failed to import bean definitions from relative location ["
83                                 + location + "]", ele, ex);
84             }
85         }
86         // 解析后进行监听器激活处理
87         Resource[] actResArray = actualResources.toArray(new Resource[actualResources.size()]);
88         getReaderContext().fireImportProcessed(location, actResArray, extractSource(ele));
89     }