ImportResource

What

ImportResource用于指示导入一个或多个包含BeanDefiniton的资源。

Usage

在资源类上声明@ImportResource注解并指定资源表达式。如classpath目录及其config、spring子目录下所有的spring-config-*.xml文件：

package org.ifinal.finalframework;

@ImportResource({
    FinalFramework.CLASS_PATH_SPRING_CONFIG_XML,
    FinalFramework.CLASS_PATH_CONFIG_SPRING_CONFIG_XML,
    FinalFramework.CLASS_PATH_SPRING_SPRING_CONFIG_XML
})
public class FinalFramework {

    static final String CLASS_PATH_SPRING_CONFIG_XML = "classpath:spring-config-*.xml";

    static final String CLASS_PATH_CONFIG_SPRING_CONFIG_XML = "classpath*:config/spring-config-*.xml";

    static final String CLASS_PATH_SPRING_SPRING_CONFIG_XML = "classpath*:spring/spring-config-*.xml";

}

也可以指定自定义的BeanDefinitionReader。

How

Process

在ConfigurationClassParser类的doProcessConfigurationClass()方法中，有如下的代码片段：

// Process any @ImportResource annotations
AnnotationAttributes importResource =
        AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);
if (importResource != null) {
    String[] resources = importResource.getStringArray("locations");
    Class<? extends BeanDefinitionReader> readerClass = importResource.getClass("reader");
    for (String resource : resources) {
        String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);
        configClass.addImportedResource(resolvedResource, readerClass);
    }
}

上述代码将@ImportResource注解中的locations和reader属性值添加到BeanDefinition中。

Load

在ConfigurationClassBeanDefinitionReader类的loadBeanDefinitionsFromImportedResources()方法中实现资源的加载。

首先，通过资源文件的类型来实例化BeanDefinitionReader，如以.groovy结尾的资源使用GroovyBeanDefinitionReader，其它资源使用XmlBeanDefinitionReader。

然后调用BeanDefinitionReader的loadBeanDefinitions方法来加载BeanDefinition。

private void loadBeanDefinitionsFromImportedResources(
        Map<String, Class<? extends BeanDefinitionReader>> importedResources) {

    Map<Class<?>, BeanDefinitionReader> readerInstanceCache = new HashMap<>();

    importedResources.forEach((resource, readerClass) -> {
        // Default reader selection necessary?
        if (BeanDefinitionReader.class == readerClass) {
            if (StringUtils.endsWithIgnoreCase(resource, ".groovy")) {
                // When clearly asking for Groovy, that's what they'll get...
                readerClass = GroovyBeanDefinitionReader.class;
            }
            else {
                // Primarily ".xml" files but for any other extension as well
                readerClass = XmlBeanDefinitionReader.class;
            }
        }

        BeanDefinitionReader reader = readerInstanceCache.get(readerClass);
        if (reader == null) {
            try {
                // Instantiate the specified BeanDefinitionReader
                reader = readerClass.getConstructor(BeanDefinitionRegistry.class).newInstance(this.registry);
                // Delegate the current ResourceLoader to it if possible
                if (reader instanceof AbstractBeanDefinitionReader) {
                    AbstractBeanDefinitionReader abdr = ((AbstractBeanDefinitionReader) reader);
                    abdr.setResourceLoader(this.resourceLoader);
                    abdr.setEnvironment(this.environment);
                }
                readerInstanceCache.put(readerClass, reader);
            }
            catch (Throwable ex) {
                throw new IllegalStateException(
                        "Could not instantiate BeanDefinitionReader class [" + readerClass.getName() + "]");
            }
        }

        // TODO SPR-6310: qualify relative path locations as done in AbstractContextLoader.modifyLocations
        reader.loadBeanDefinitions(resource);
    });
}