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
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; } |
@EnableAutoConfiguration注解来注册项目包外的bean。而spring.factories文件,则是用来记录项目包外需要注册的bean类名
为什么需要spring.factories文件,
因为我们整个项目里面的入口文件只会扫描整个项目里面下的@Compont @Configuration等注解
但是如果我们是引用了其他jar包,而其他jar包只有@Bean或者@Compont等注解,是不会扫描到的。
除非你引入的jar包没有Bean加载到容器当中
所以我们是通过写/META-INF/spring.factories文件去进行加载的。
以上为个人经验,希望能给大家一个参考,也希望大家多多支持服务器之家。
原文链接:https://kingkong.blog.csdn.net/article/details/104491907