/**
 * Class that can be used to bootstrap and launch a Spring application from a Java main
 * method. By default class will perform the following steps to bootstrap your
 * application:
 *
 * <ul>
 * <li>Create an appropriate {@link ApplicationContext} instance (depending on your
 * classpath)</li>
 * <li>Register a {@link CommandLinePropertySource} to expose command line arguments as
 * Spring properties</li>
 * <li>Refresh the application context, loading all singleton beans</li>
 * <li>Trigger any {@link CommandLineRunner} beans</li>
 * </ul>
 *
 * In most circumstances the static {@link #run(Class, String[])} method can be called
 * directly from your {@literal main} method to bootstrap your application:
 *
 * <pre class="code">
 * &#064;Configuration
 * &#064;EnableAutoConfiguration
 * public class MyApplication  {
 *
 *   // ... Bean definitions
 *
 *   public static void main(String[] args) throws Exception {*     SpringApplication.run(MyApplication.class, args);
 *   }
 * }
 * </pre>
 *
 * <p>
 * For more advanced configuration a {@link SpringApplication} instance can be created and
 * customized before being run:
 *
 * <pre class="code">
 * public static void main(String[] args) throws Exception {*   SpringApplication application = new SpringApplication(MyApplication.class);
 *   // ... customize application settings here
 *   application.run(args)
 * }
 * </pre>
 *
 * {@link SpringApplication}s can read beans from a variety of different sources. It is
 * generally recommended that a single {@code @Configuration} class is used to bootstrap
 * your application, however, you may also set {@link #getSources()sources} from:
 * <ul>
 * <li>The fully qualified class name to be loaded by
 * {@link AnnotatedBeanDefinitionReader}</li>
 * <li>The location of an XML resource to be loaded by {@link XmlBeanDefinitionReader}, or
 * a groovy script to be loaded by {@link GroovyBeanDefinitionReader}</li>
 * <li>The name of a package to be scanned by {@link ClassPathBeanDefinitionScanner}</li>
 * </ul>
 *
 * Configuration properties are also bound to the {@link SpringApplication}. This makes it
 * possible to set {@link SpringApplication} properties dynamically, like additional
 * sources ("spring.main.sources" - a CSV list) the flag to indicate a web environment
 * ("spring.main.web-application-type=none") or the flag to switch off the banner
 * ("spring.main.banner-mode=off").
 */

private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
        Class<?>[] parameterTypes, Object... args) {
    ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
    // Use names and ensure unique to protect against duplicates
    Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));            // 获取指定类型的工厂名字
    List<T> instances = createSpringFactoriesInstances(type, parameterTypes,    // 根据名字、类型创建工厂实例
            classLoader, args, names);
    AnnotationAwareOrderComparator.sort(instances);
    return instances;
}

private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
    MultiValueMap<String, String> result = cache.get(classLoader);
    if (result != null) {
        return result;
    }
</span><span style="color: rgba(0, 0, 255, 1)">try</span><span style="color: rgba(0, 0, 0, 1)"> {
    Enumeration</span>&lt;URL&gt; urls = (classLoader != <span style="color: rgba(0, 0, 255, 1)">null</span> ?<span style="color: rgba(0, 0, 0, 1)">
            classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
            ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> classLoader.getResources(FACTORIES_RESOURCE_LOCATION)获取类路径下全部的META-INF/spring.factories的URL</span>
    result = <span style="color: rgba(0, 0, 255, 1)">new</span> LinkedMultiValueMap&lt;&gt;<span style="color: rgba(0, 0, 0, 1)">();
    </span><span style="color: rgba(0, 0, 255, 1)">while</span> (urls.hasMoreElements()) {                                        <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 遍历全部的URL，逐个读取META-INF/spring.factories中的属性</span>
        URL url =<span style="color: rgba(0, 0, 0, 1)"> urls.nextElement();
        UrlResource resource </span>= <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> UrlResource(url);
        Properties properties </span>=<span style="color: rgba(0, 0, 0, 1)"> PropertiesLoaderUtils.loadProperties(resource);
        </span><span style="color: rgba(0, 0, 255, 1)">for</span> (Map.Entry&lt;?, ?&gt;<span style="color: rgba(0, 0, 0, 1)"> entry : properties.entrySet()) {
            List</span>&lt;String&gt; factoryClassNames =<span style="color: rgba(0, 0, 0, 1)"> Arrays.asList(
                    StringUtils.commaDelimitedListToStringArray((String) entry.getValue()));
            result.addAll((String) entry.getKey(), factoryClassNames);        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 属性全部放入MultiValueMap&lt;String, String&gt; result中，注意result的类型</span>

            }
}
cache.put(classLoader, result);                                            // 结果放入缓存，方便下次查找
return result;
}
catch (IOException ex) {
throw new IllegalArgumentException("Unable to load factories from location [" +
FACTORIES_RESOURCE_LOCATION + "]", ex);
}
}