springboot 加載 META-INF/spring.factories
用戶應用程序Application
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ConfigurableApplicationContext context = SpringApplication.run(NacosSpringBootYamlApplication.class, args); |
SpringApplication類
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public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) { return run(new Class<?>[] { primarySource }, args); } |
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// 這里Class是數組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)); // 這里就是SpringMvcApplication的實例 this.webApplicationType = WebApplicationType.deduceFromClasspath();// deduce(推斷)web類型(servlet、reactive、NoWeb) setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));// 這里會處理加載所有的spring.factories文件的內容到緩存 找到*META-INF/spring.factories*中聲明的所有ApplicationContextInitializer的實現類并將其實例化 setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class)); //找到*META-INF/spring.factories*中聲明的所有ApplicationListener的實現類并將其實例化 this.mainApplicationClass = deduceMainApplicationClass(); //獲得當前執行main方法的類對象，這里就是SpringMvcApplication的實例 } |
具體加載該classLoader下的所有spring.factories到緩存
如果緩存已經存在，則直接根據key，返回數據
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/** key:是spring.factories的key value:是根據key分組，把同個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) { //已經處理過了 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的內容 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根據逗號，分隔 result.add(factoryClassName, factoryName.trim()); //factoryClassName其實就是spring.factories的key 由于value是List類型 MultiValueMap value有多個 } } } cache.put(classLoader, result); return result; } catch (IOException ex) { throw new IllegalArgumentException("Unable to load factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex); } } |
流程圖
建立META-INF/spring.factories文件的意義何在
平常我們如何將Bean注入到容器當中
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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,里面通過@Bean進行加載bean
或者使用@Compont注解在類上進行類的注入
注意：
在我們主程序入口的時候：
@SpringBootApplication這個注解里面的東西
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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注解指掃描@SpringBootApplication注解的入口程序類所在的basepackage下的
所有帶有@Component注解的bean，從而注入到容器當中。
但是
如果是加入maven坐標依賴的jar包，就是項目根目錄以外的Bean是怎么添加的？？
這個時候注解@EnableAutoConfiguration的作用就來了
導入了AutoConfigurationImportSelector這個類：
這個類里面有一個方法
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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注解來注冊項目包外的bean。而spring.factories文件，則是用來記錄項目包外需要注冊的bean類名
為什么需要spring.factories文件，
因為我們整個項目里面的入口文件只會掃描整個項目里面下的@Compont @Configuration等注解
但是如果我們是引用了其他jar包，而其他jar包只有@Bean或者@Compont等注解，是不會掃描到的。
除非你引入的jar包沒有Bean加載到容器當中
所以我們是通過寫/META-INF/spring.factories文件去進行加載的。
以上為個人經驗，希望能給大家一個參考，也希望大家多多支持服務器之家。
原文鏈接：https://kingkong.blog.csdn.net/article/details/104491907
