SpringBoot之十六：SpringBoot自动配置的原理

蔚落 2022-05-28 10:57 47阅读 0赞

> Spring Boot在进行SpringApplication对象实例化时会加载**META-INF/spring.factories文件**，将该配置文件中的配置载入到Spring容器。

\#\#一、初始化加载

\#\#\#1、首先实例化SpringApplication 对象

@SpringBootApplication
    public class App {	
    /**
     * 在main方法中启动我们的应用程序
     * @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、在有参构造中初始化配置

/**
     * 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);
    		}
    	}

加载到了自动配置的文件：

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);
    		}
    	}

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