Spring Boot在進行SpringApplication物件例項化時會載入META-INF/spring.factories檔案，將該配置檔案中的配置載入到Spring容器。

一、初始化載入

1、首先例項化SpringApplication 物件

@SpringBootApplication
public class App {  
/**
 * 在main方法中啟動我們的應用程式
 * @param args
 */
public static void main(String[] args) {

    SpringApplication app=new SpringApplication(App.class);
    app.setBannerMode(Banner.Mode.OFF);
    app.run(App.class, args);
    //SpringApplication.run(App.class, args);
 

}
}

2、在有參構造中初始化配置

/**
 * Create a new {@link SpringApplication} instance. The application context will load
 * beans from the specified sources (see {@link SpringApplication class-level}
 * documentation for details. The instance can be customized before calling
 * {@link #run(String...)}.
 * @param
 
 sources the bean sources
 * @see #run(Object, String[])
 * @see #SpringApplication(ResourceLoader, Object...)
 */
public SpringApplication(Object... sources) {
    initialize(sources);
}

3、初始化方法

@SuppressWarnings({ "unchecked", "rawtypes" })
private void initialize(Object[] sources) {
    if (sources != null
 
 && sources.length > 0) {
        this.sources.addAll(Arrays.asList(sources));
    }
    this.webEnvironment = deduceWebEnvironment();
    setInitializers((Collection) getSpringFactoriesInstances(
            ApplicationContextInitializer.class));
    setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
    this.mainApplicationClass = deduceMainApplicationClass();
}

4、getSpringFactoriesInstances方法

private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type) {
    return getSpringFactoriesInstances(type, new Class<?>[] {});
}

private <T> Collection<? extends 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<String>(
            SpringFactoriesLoader.loadFactoryNames(type, classLoader));
    List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
            classLoader, args, names);
    AnnotationAwareOrderComparator.sort(instances);
    return instances;
    }

public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
        String factoryClassName = factoryClass.getName();
        try {
            Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
                    ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
            List<String> result = new ArrayList<String>();
            while (urls.hasMoreElements()) {
                URL url = urls.nextElement();
                Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
                String factoryClassNames = properties.getProperty(factoryClassName);
                result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
            }
            return result;
        }
        catch (IOException ex) {
            throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() +
                    "] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex);
        }
    }

載入到了自動配置的檔案：

public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";

public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
        String factoryClassName = factoryClass.getName();
        try {
            Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
                    ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
            List<String> result = new ArrayList<String>();
            while (urls.hasMoreElements()) {
                URL url = urls.nextElement();
                Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
                String factoryClassNames = properties.getProperty(factoryClassName);
                result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
            }
            return result;
        }
        catch (IOException ex) {
            throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() +
                    "] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex);
        }
    }