springboot|springboot 加载 META-INF/spring.factories方式 springboot加载META-INF

springboot 加载 META-INF/spring.factories

用户应用程序Application

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

springboot 加载 META-INF/spring.factories
用户应用程序Application

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

SpringApplication类

public static ConfigurableApplicationContext run(Class primarySource, String... args) {return run(new Class[] { primarySource }, args); }

// 这里Class是数组public static ConfigurableApplicationContext run(Class[] primarySources, String[] args) {return new SpringApplication(primarySources).run(args); }

public SpringApplication(Class... primarySources) {this(null, primarySources); }

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

/** key:是spring.factories的keyvalue:是根据key分组，把同个key的不同value放到list里面 */ private static Map> loadSpringFactories(@Nullable ClassLoader classLoader) {MultiValueMap 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.factoriestry { //得到classloader下的所有jar包中的spring.factories的文件Enumeration 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keyvalue: spring.factories的valueString factoryClassName = ((String) entry.getKey()).trim(); // spring.factories的keyfor (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|springboot 加载 META-INF/spring.factories方式

文章图片

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

@Configuration@EnableConfigurationProperties(HelloProperties.class)public class HelloServiceAutoConfiguration {@AutowiredHelloProperties helloProperties; @Beanpublic 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

@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

/*** 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 getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {List 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。
【springboot|springboot 加载 META-INF/spring.factories方式】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脚本之家。