springboot 加载 META-INF/spring.factories方式

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springboot 加载 META-INF/spring.factories

用户应用程序Application

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									ConfigurableApplicationContext context = SpringApplication.run(NacosSpringBootYamlApplication.class, args);

SpringApplication类

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									public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {

									  return run(new Class<?>[] { primarySource }, args);

									 }

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									// 这里Class是数组

									public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {

									  return new SpringApplication(primarySources).run(args);

									 }

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									public SpringApplication(Class<?>... primarySources) {

									  this(null, primarySources);

									 }

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									public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {

									  this.resourceLoader = resourceLoader;

									  Assert.notNull(primarySources, "PrimarySources must not be null");

									  this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources)); // 这里就是SpringMvcApplication的实例

									  this.webApplicationType = WebApplicationType.deduceFromClasspath();// deduce(推断)web类型(servlet、reactive、NoWeb)

									  setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));// 这里会处理加载所有的spring.factories文件的内容到缓存 找到*META-INF/spring.factories*中声明的所有ApplicationContextInitializer的实现类并将其实例化

									  setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class)); //找到*META-INF/spring.factories*中声明的所有ApplicationListener的实现类并将其实例化

									  this.mainApplicationClass = deduceMainApplicationClass(); //获得当前执行main方法的类对象，这里就是SpringMvcApplication的实例

									 }

具体加载该classLoader下的所有spring.factories到缓存

如果缓存已经存在，则直接根据key，返回数据

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									/** key:是spring.factories的key    value:是根据key分组，把同个key的不同value放到list里面 */

									 private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {

									  MultiValueMap<String, String> result = cache.get(classLoader);

									  if (result != null) { //已经处理过了  直接返回

									   return result;

									  }

									//url: // file:/C:/Users/kongqi/.m2/repository/org/springframework/spring-beans/5.1.9.RELEASE/spring-beans-5.1.9.RELEASE.jar!/META-INF/spring.factories

									  try { //得到classloader下的所有jar包中的spring.factories的文件

									   Enumeration<URL> urls = (classLoader != null ?

									     classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :

									     ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));

									   result = new LinkedMultiValueMap<>();

									   while (urls.hasMoreElements()) {

									    URL url = urls.nextElement();

									    UrlResource resource = new UrlResource(url);

									    Properties properties = PropertiesLoaderUtils.loadProperties(resource); // 得到spring.factories的内容

									    for (Map.Entry<?, ?> entry : properties.entrySet()) { // key: spring.factories的key  value: spring.factories的value

									     String factoryClassName = ((String) entry.getKey()).trim(); // spring.factories的key

									     for (String factoryName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {//value根据逗号，分隔

									      result.add(factoryClassName, factoryName.trim()); //factoryClassName其实就是spring.factories的key   由于value是List类型 MultiValueMap value有多个

									     }

									    }

									   }

									   cache.put(classLoader, result);

									   return result;

									  }

									  catch (IOException ex) {

									   throw new IllegalArgumentException("Unable to load factories from location [" +

									     FACTORIES_RESOURCE_LOCATION + "]", ex);

									  }

									 }

流程图

springboot 加载 META-INF/spring.factories方式

建立META-INF/spring.factories文件的意义何在

平常我们如何将Bean注入到容器当中

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									@Configuration

									@EnableConfigurationProperties(HelloProperties.class)

									public class HelloServiceAutoConfiguration {

									    @Autowired

									    HelloProperties helloProperties;

									    @Bean

									    public HelloService helloService() {

									        HelloService service = new HelloService();

									        service.setHelloProperties( helloProperties  );

									        return service;

									    }

									}

一般就建立配置文件使用@Configuration,里面通过@Bean进行加载bean

或者使用@Compont注解在类上进行类的注入

注意：

在我们主程序入口的时候：

@SpringBootApplication这个注解里面的东西

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									@Target(ElementType.TYPE)

									@Retention(RetentionPolicy.RUNTIME)

									@Documented

									@Inherited

									@SpringBootConfiguration

									@EnableAutoConfiguration

									@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),

									        @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })

									public @interface SpringBootApplication {

里面注解@EnableAutoConfiguration

@ComponentScan注解指扫描@SpringBootApplication注解的入口程序类所在的basepackage下的

所有带有@Component注解的bean，从而注入到容器当中。

但是

如果是加入maven坐标依赖的jar包，就是项目根目录以外的Bean是怎么添加的？？

这个时候注解@EnableAutoConfiguration的作用就来了

导入了AutoConfigurationImportSelector这个类：

这个类里面有一个方法

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									/**

									 * Return the auto-configuration class names that should be considered. By default

									 * this method will load candidates using {@link SpringFactoriesLoader} with

									 * {@link #getSpringFactoriesLoaderFactoryClass()}.

									 * @param metadata the source metadata

									 * @param attributes the {@link #getAttributes(AnnotationMetadata) annotation

									 * attributes}

									 * @return a list of candidate configurations

									 */

									protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {

									    List<String> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),

									            getBeanClassLoader());

									    Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you "

									            + "are using a custom packaging, make sure that file is correct.");

									    return configurations;

									}