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一、前言二、容器启动2.1 @SpringBootApplication注解2.2 SpringApplication.run()静态方法如上图,容器启动流程可以分为5个主要步骤：1.getRunListeners获取监听器（SpringApplicationRunListeners ）载入工厂名称（loadFactoryNames）创建spring工厂实例（createSpringFactoriesInstances）2.准备好环境3.准备上下文4.刷新上下文5.刷新完上下文后三、总结

正文

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一、前言

spring cloud大行其道的当下，如果不了解基本原理那么是很纠结的(看见的都是约定大于配置，但是原理呢？为什么要这么做？如何串联起来的？)。spring cloud是基于spring boot快速搭建的，今天咱们就看看spring boot容器启动流程(全文基于1.5.9版本，springboot2基本一致)。(本文不讲解如何快速启动spring boot，那些直接官方看即可，官网文档飞机票)

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二、容器启动

spring boot一般是指定容器启动main方法，然后以命令行方式启动Jar包，如下图：

1 @SpringBootApplication2 public class Application {3     public static void main(String[] args) {4         SpringApplication.run(Application.class, args);5     }6 }

这里核心关注2个东西：

1.@SpringBootApplication注解

2.SpringApplication.run()静态方法

下面我们就分别探究这两块内容。

2.1@SpringBootApplication注解

源码如下：

 1 @Target(ElementType.TYPE) 2 @Retention(RetentionPolicy.RUNTIME) 3 @Documented 4 @Inherited 5 @SpringBootConfiguration 6 @EnableAutoConfiguration 7 @ComponentScan(excludeFilters = { 8         @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class), 9         @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })10 public @interface SpringBootApplication {

核心注解：

@SpringBootConfiguration（实际就是个@Configuration）：表示这是一个JavaConfig配置类，可以在这个类中自定义bean,依赖关系等。-》这个是spring-boot特有的注解，常用到。@EnableAutoConfiguration：借助@Import的帮助，将所有符合自动配置条件的bean定义加载到IoC容器（建议放在根包路径下，这样可以扫描子包和类）。-》这个需要详细深挖！@ComponentScan：spring的自动扫描注解，可定义扫描范围，加载到IOC容器。-》这个不多说，spring的注解大家肯定眼熟其中@EnableAutoConfiguration这个注解的源码：

1 @SuppressWarnings("deprecation")2 @Target(ElementType.TYPE)3 @Retention(RetentionPolicy.RUNTIME)4 @Documented5 @Inherited6 @AutoConfigurationPackage7 @Import(EnableAutoConfigurationImportSelector.class)8 public @interface EnableAutoConfiguration {

核心是一个EnableAutoConfigurationImportSelector类图如下：

核心方法在顶级接口ImportSelector的selectImports（），源码如下：

 1 @Override 2     public String[] selectImports(AnnotationMetadata annotationMetadata) { 3         if (!isEnabled(annotationMetadata)) { 4             return NO_IMPORTS; 5         } 6         try {         //1.从META-INF/spring-autoconfigure-metadata.properties文件中载入483条配置属性（有一些有默认值）， 7             AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader 8                     .loadMetadata(this.beanClassLoader); 9             AnnotationAttributes attributes = getAttributes(annotationMetadata);//2.获取注解属性10             List<String> configurations = getCandidateConfigurations(annotationMetadata,//3.获取97个自动配置类11                     attributes);12             configurations = removeDuplicates(configurations);//4.移除重复的13             configurations = sort(configurations, autoConfigurationMetadata);//5.排序14             Set<String> exclusions = getExclusions(annotationMetadata, attributes);//6.获取需要排除的15             checkExcludedClasses(configurations, exclusions);//7.校验排除类16             configurations.removeAll(exclusions);//8.删除所有需要排除的17             configurations = filter(configurations, autoConfigurationMetadata);//9.过滤器OnClassCondition（注解中配置的当存在某类才生效）18             fireAutoConfigurationImportEvents(configurations, exclusions);//10.触发自动配置导入监听事件19             return configurations.toArray(new String[configurations.size()]);20         }21         catch (IOException ex) {22             throw new IllegalStateException(ex);23         }24     }

这里注意3个核心方法：

1）loadMetadata 加载配置

其实就是用类加载器去加载：META-INF/spring-autoconfigure-metadata.properties（spring-boot-autoconfigure-1.5.9.RELEASE-sources.jar）文件中定义的配置，返回PropertiesAutoConfigurationMetadata（实现了AutoConfigurationMetadata接口，封装了属性的get set方法）

2）getCandidateConfigurations获取默认支持的自动配置类名列表

自动配置灵魂方法，SpringFactoriesLoader.loadFactoryNames 从META-INF/spring.factories（spring-boot-autoconfigure-1.5.9.RELEASE-sources.jar）文件中获取自动配置类key=EnableAutoConfiguration.class的配置。

 1 protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, 2             AnnotationAttributes attributes) {//话说这里2个入参没啥用啊...谁来给我解释一下... 3         List<String> configurations = SpringFactoriesLoader.loadFactoryNames( 4                 getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader()); 5         Assert.notEmpty(configurations, 6                 "No auto configuration classes found in META-INF/spring.factories. If you " 7                         + "are using a custom packaging, make sure that file is correct."); 8         return configurations; 9     }10 //返回的是EnableAutoConfiguration类11 protected Class<?> getSpringFactoriesLoaderFactoryClass() {12         return EnableAutoConfiguration.class;13     }

实际获取了什么？spring.factories文件如下，实际获取了# Auto Configure自动配置模块的所有类。

# Initializersorg.springframework.context.ApplicationContextInitializer=\org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\org.springframework.boot.autoconfigure.logging.AutoConfigurationReportLoggingInitializer# Application Listenersorg.springframework.context.ApplicationListener=\org.springframework.boot.autoconfigure.BackgroundPreinitializer# Auto Configuration Import Listenersorg.springframework.boot.autoconfigure.AutoConfigurationImportListener=\org.springframework.boot.autoconfigure.condition.ConditionEvaluationReportAutoConfigurationImportListener# Auto Configuration Import Filtersorg.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\org.springframework.boot.autoconfigure.condition.OnClassCondition# Auto Configure ===========这里就是全部的自动配置类===============================org.springframework.boot.autoconfigure.EnableAutoConfiguration=\org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\org.springframework.boot.autoconfigure.cloud.CloudAutoConfiguration,\org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,\org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,\org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,\org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchAutoConfiguration,\org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.ldap.LdapDataAutoConfiguration,\org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration,\org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration,\org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration,\org.springframework.boot.autoconfigure.elasticsearch.jest.JestAutoConfiguration,\org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,\org.springframework.boot.autoconfigure.h2.H2ConsoleAutoConfiguration,\org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,\org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,\org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,\org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,\org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration,\org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,\org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,\org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,\org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,\org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,\org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,\org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,\org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,\org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration,\org.springframework.boot.autoconfigure.mobile.DeviceResolverAutoConfiguration,\org.springframework.boot.autoconfigure.mobile.DeviceDelegatingViewResolverAutoConfiguration,\org.springframework.boot.autoconfigure.mobile.SitePreferenceAutoConfiguration,\org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\org.springframework.boot.autoconfigure.reactor.ReactorAutoConfiguration,\org.springframework.boot.autoconfigure.security.SecurityAutoConfiguration,\org.springframework.boot.autoconfigure.security.SecurityFilterAutoConfiguration,\org.springframework.boot.autoconfigure.security.FallbackWebSecurityAutoConfiguration,\org.springframework.boot.autoconfigure.security.oauth2.OAuth2AutoConfiguration,\org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\org.springframework.boot.autoconfigure.social.SocialWebAutoConfiguration,\org.springframework.boot.autoconfigure.social.FacebookAutoConfiguration,\org.springframework.boot.autoconfigure.social.LinkedInAutoConfiguration,\org.springframework.boot.autoconfigure.social.TwitterAutoConfiguration,\org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,\org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\org.springframework.boot.autoconfigure.web.DispatcherServletAutoConfiguration,\org.springframework.boot.autoconfigure.web.EmbeddedServletContainerAutoConfiguration,\org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration,\org.springframework.boot.autoconfigure.web.HttpEncodingAutoConfiguration,\org.springframework.boot.autoconfigure.web.HttpMessageConvertersAutoConfiguration,\org.springframework.boot.autoconfigure.web.MultipartAutoConfiguration,\org.springframework.boot.autoconfigure.web.ServerPropertiesAutoConfiguration,\org.springframework.boot.autoconfigure.web.WebClientAutoConfiguration,\org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration,\org.springframework.boot.autoconfigure.websocket.WebSocketAutoConfiguration,\org.springframework.boot.autoconfigure.websocket.WebSocketMessagingAutoConfiguration,\org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration============================================end================================================# Failure analyzersorg.springframework.boot.diagnostics.FailureAnalyzer=\org.springframework.boot.autoconfigure.diagnostics.analyzer.NoSuchBeanDefinitionFailureAnalyzer,\org.springframework.boot.autoconfigure.jdbc.DataSourceBeanCreationFailureAnalyzer,\org.springframework.boot.autoconfigure.jdbc.HikariDriverConfigurationFailureAnalyzer# Template availability providersorg.springframework.boot.autoconfigure.template.TemplateAvailabilityProvider=\org.springframework.boot.autoconfigure.freemarker.FreeMarkerTemplateAvailabilityProvider,\org.springframework.boot.autoconfigure.mustache.MustacheTemplateAvailabilityProvider,\org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAvailabilityProvider,\org.springframework.boot.autoconfigure.thymeleaf.ThymeleafTemplateAvailabilityProvider,\org.springframework.boot.autoconfigure.web.JspTemplateAvailabilityProvider

3）filter过滤器 根据OnClassCondition注解把不满足条件的过滤掉

 1 private List<String> filter(List<String> configurations, 2             AutoConfigurationMetadata autoConfigurationMetadata) { 3         long startTime = System.nanoTime(); 4         String[] candidates = configurations.toArray(new String[configurations.size()]); 5         boolean[] skip = new boolean[candidates.length]; 6         boolean skipped = false;           //获取需要过滤的自动配置导入拦截器，spring.factories配置中就一个：org.springframework.boot.autoconfigure.condition.OnClassCondition 7         for (AutoConfigurationImportFilter filter : getAutoConfigurationImportFilters()) { 8             invokeAwareMethods(filter); 9             boolean[] match = filter.match(candidates, autoConfigurationMetadata);10             for (int i = 0; i < match.length; i++) {11                 if (!match[i]) {12                     skip[i] = true;13                     skipped = true;14                 }15             }16         }17         if (!skipped) {//多条件只要有一个不匹配->skipped = true，全部匹配-》skipped = false->直接返回18             return configurations;19         }20         List<String> result = new ArrayList<String>(candidates.length);21         for (int i = 0; i < candidates.length; i++) {22             if (!skip[i]) {//匹配-》不跳过-》添加进result23                 result.add(candidates[i]);24             }25         }26         if (logger.isTraceEnabled()) {27             int numberFiltered = configurations.size() - result.size();28             logger.trace("Filtered " + numberFiltered + " auto configuration class in "29                     + TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startTime)30                     + " ms");31         }32         return new ArrayList<String>(result);33     }

2.2SpringApplication.run()静态方法

SpringApplication.run

 1 public ConfigurableApplicationContext run(String... args) { 2         StopWatch stopWatch = new StopWatch(); 3         stopWatch.start(); 4         ConfigurableApplicationContext context = null; 5         FailureAnalyzers analyzers = null; 6         configureHeadlessProperty(); 7         SpringApplicationRunListeners listeners = getRunListeners(args);//1.获取监听器 8         listeners.starting();-->启动！ 9         try {10             ApplicationArguments applicationArguments = new DefaultApplicationArguments(11                     args);12             ConfigurableEnvironment environment = prepareEnvironment(listeners,//2.准备好环境，触发ApplicationEnvironmentPreparedEvent事件13                     applicationArguments);14             Banner printedBanner = printBanner(environment);//打印启动提示字符，默认spring的字符图15             context = createApplicationContext();//实例化一个可配置应用上下文16             analyzers = new FailureAnalyzers(context);17             prepareContext(context, environment, listeners, applicationArguments,//3.准备上下文18                     printedBanner);19             refreshContext(context);//4.刷新上下文20             afterRefresh(context, applicationArguments);//5.刷新上下文后21             listeners.finished(context, null);--关闭！22             stopWatch.stop();23             if (this.logStartupInfo) {24                 new StartupInfoLogger(this.mainApplicationClass)25                         .logStarted(getApplicationLog(), stopWatch);26             }27             return context;28         }29         catch (Throwable ex) {30             handleRunFailure(context, listeners, analyzers, ex);31             throw new IllegalStateException(ex);32         }33     }

如上图,容器启动流程可以分为5个主要步骤：1.getRunListeners获取监听器（SpringApplicationRunListeners）

实际是SpringApplicationRunListener类

 1 private SpringApplicationRunListeners getRunListeners(String[] args) { 2     Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class }; 3     return new SpringApplicationRunListeners(logger, getSpringFactoriesInstances( 4             SpringApplicationRunListener.class, types, this, args)); 5 } 6  7 private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type) { 8     return getSpringFactoriesInstances(type, new Class<?>[] {}); 9 }10 11 private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type,12         Class<?>[] parameterTypes, Object... args) {13     ClassLoader classLoader = Thread.currentThread().getContextClassLoader();14     // 使用Set确保的字符串的唯一性15     Set<String> names = new LinkedHashSet<String>(16             SpringFactoriesLoader.loadFactoryNames(type, classLoader));// 1.载入工厂名称集合17     List<T> instances = createSpringFactoriesInstances(type, parameterTypes,// 2.创建工厂实例18             classLoader, args, names);19     AnnotationAwareOrderComparator.sort(instances);// 排序20     return instances;21 }

载入工厂名称（loadFactoryNames）

当前类的类加载器从META-INF/spring.factories文件中获取SpringApplicationRunListener类的配置

 1 public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) { 2         String factoryClassName = factoryClass.getName(); 3         try { 4             Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) : 5                     ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION)); 6             List<String> result = new ArrayList<String>(); 7             while (urls.hasMoreElements()) { 8                 URL url = urls.nextElement(); 9                 Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));10                 String factoryClassNames = properties.getProperty(factoryClassName);11                 result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));12             }13             return result;14         }15         catch (IOException ex) {16             throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() +17                     "] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex);18         }19     }

上图，获取到工厂类名后，下面来看看META-INF/spring.factories中定义了啥：

# PropertySource Loadersorg.springframework.boot.env.PropertySourceLoader=\org.springframework.boot.env.PropertiesPropertySourceLoader,\org.springframework.boot.env.YamlPropertySourceLoader# Run Listeners  这里呢，看这里！！！！org.springframework.boot.SpringApplicationRunListener=\org.springframework.boot.context.event.EventPublishingRunListener# Application Context Initializersorg.springframework.context.ApplicationContextInitializer=\org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\org.springframework.boot.context.ContextIdApplicationContextInitializer,\org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\org.springframework.boot.context.embedded.ServerPortInfoApplicationContextInitializer# Application Listenersorg.springframework.context.ApplicationListener=\org.springframework.boot.ClearCachesApplicationListener,\org.springframework.boot.builder.ParentContextCloserApplicationListener,\org.springframework.boot.context.FileEncodingApplicationListener,\org.springframework.boot.context.config.AnsiOutputApplicationListener,\org.springframework.boot.context.config.ConfigFileApplicationListener,\org.springframework.boot.context.config.DelegatingApplicationListener,\org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener,\org.springframework.boot.logging.ClasspathLoggingApplicationListener,\org.springframework.boot.logging.LoggingApplicationListener# Environment Post Processorsorg.springframework.boot.env.EnvironmentPostProcessor=\org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor# Failure Analyzersorg.springframework.boot.diagnostics.FailureAnalyzer=\org.springframework.boot.diagnostics.analyzer.BeanCurrentlyInCreationFailureAnalyzer,\org.springframework.boot.diagnostics.analyzer.BeanNotOfRequiredTypeFailureAnalyzer,\org.springframework.boot.diagnostics.analyzer.BindFailureAnalyzer,\org.springframework.boot.diagnostics.analyzer.ConnectorStartFailureAnalyzer,\org.springframework.boot.diagnostics.analyzer.NoUniqueBeanDefinitionFailureAnalyzer,\org.springframework.boot.diagnostics.analyzer.PortInUseFailureAnalyzer,\org.springframework.boot.diagnostics.analyzer.ValidationExceptionFailureAnalyzer# FailureAnalysisReportersorg.springframework.boot.diagnostics.FailureAnalysisReporter=\org.springframework.boot.diagnostics.LoggingFailureAnalysisReporter

哇，都是些类全名称，且key都是接口，value都是实现类。我们根据key=“org.springframework.boot.SpringApplicationRunListener”查询得到实现类value="org.springframework.boot.context.event.EventPublishingRunListener"事件发布启动监听器，一猜也知道肯定要用”反射”根据类名获取类实例，下面很快得到验证...

创建spring工厂实例（createSpringFactoriesInstances）

根据第一步得到的Set<String> names（SpringApplicationRunListener的唯一实现类EventPublishingRunListener）生成"事件发布启动监听器"工厂实例

 1 @SuppressWarnings("unchecked") 2     private <T> List<T> createSpringFactoriesInstances(Class<T> type, 3             Class<?>[] parameterTypes, ClassLoader classLoader, Object[] args, 4             Set<String> names) { 5         List<T> instances = new ArrayList<T>(names.size()); 6         for (String name : names) { 7             try { 8                 Class<?> instanceClass = ClassUtils.forName(name, classLoader);// 利用反射获取类 9                 Assert.isAssignable(type, instanceClass);10                 Constructor<?> constructor = instanceClass11                         .getDeclaredConstructor(parameterTypes);// 得到构造器12                 T instance = (T) BeanUtils.instantiateClass(constructor, args);// 根据构造器和参数构造实例13                 instances.add(instance);14             }15             catch (Throwable ex) {16                 throw new IllegalArgumentException(17                         "Cannot instantiate " + type + " : " + name, ex);18             }19         }20         return instances;21     }

2.准备好环境

构造一个ConfigurableEnvironment,这里不多说。

3.准备上下文

 1 private void prepareContext(ConfigurableApplicationContext context, 2             ConfigurableEnvironment environment, SpringApplicationRunListeners listeners, 3             ApplicationArguments applicationArguments, Banner printedBanner) { 4         context.setEnvironment(environment); 5         postProcessApplicationContext(context);//单例一个BeanNameGenerator，把ResourceLoader设置进应用上下文 6         applyInitializers(context);//执行初始化器 7         listeners.contextPrepared(context);// 监听器执行上下文"已准备好"方法 8         if (this.logStartupInfo) { 9             logStartupInfo(context.getParent() == null);10             logStartupProfileInfo(context);11         }12 13         // 添加spring boot特殊单例bean14         context.getBeanFactory().registerSingleton("springApplicationArguments",15                 applicationArguments);16         if (printedBanner != null) {17             context.getBeanFactory().registerSingleton("springBootBanner", printedBanner);18         }19 20         // 载入资源21         Set<Object> sources = getSources();22         Assert.notEmpty(sources, "Sources must not be empty");23         load(context, sources.toArray(new Object[sources.size()]));24         listeners.contextLoaded(context);// 监听器执行"上下文已加载"方法25     }

4.刷新上下文

 1 private void refreshContext(ConfigurableApplicationContext context) { 2     refresh(context);//核心类 3     if (this.registerShutdownHook) { 4         try { 5             context.registerShutdownHook();//注册关闭钩子，容器关闭时执行 6         } 7         catch (AccessControlException ex) { 8             // Not allowed in some environments. 9         }10     }11 }12 13 protected void refresh(ApplicationContext applicationContext) {14     Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);15     ((AbstractApplicationContext) applicationContext).refresh();16 }

最终执行的是AbstractApplicationContext抽象类的refresh方法。

 1 public void refresh() throws BeansException, IllegalStateException { 2         synchronized (this.startupShutdownMonitor) { 3             //准备刷新的上下文环境，例如对系统属性或者环境变量进行准备及验证。 4             prepareRefresh(); 5  6             //启动子类的refreshBeanFactory方法.解析xml 7             ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); 8  9             //为BeanFactory配置容器特性，例如类加载器、事件处理器等.10             prepareBeanFactory(beanFactory);11 12             try {13                 //设置BeanFactory的后置处理. 空方法，留给子类拓展用。 14                 postProcessBeanFactory(beanFactory);15 16                 //调用BeanFactory的后处理器, 这些后处理器是在Bean定义中向容器注册的.  17                 invokeBeanFactoryPostProcessors(beanFactory);18 19                 //注册Bean的后处理器, 在Bean创建过程中调用.  20                 registerBeanPostProcessors(beanFactory);21 22                 //初始化上下文中的消息源，即不同语言的消息体进行国际化处理  23                 initMessageSource();24 25                 //初始化ApplicationEventMulticaster bean,应用事件广播器26                 initApplicationEventMulticaster();27 28                 //初始化其它特殊的Bean， 空方法，留给子类拓展用。 29                 onRefresh();30 31                 //检查并向容器注册监听器Bean32                 registerListeners();33 34                 //实例化所有剩余的(non-lazy-init) 单例Bean.35                 finishBeanFactoryInitialization(beanFactory);36 37                 //发布容器事件, 结束refresh过程. 38                 finishRefresh();39             }40 41             catch (BeansException ex) {42                 if (logger.isWarnEnabled()) {43                     logger.warn("Exception encountered during context initialization - " +44                             "cancelling refresh attempt: " + ex);45                 }46 47                 //销毁已经创建的单例Bean, 以避免资源占用.48                 destroyBeans();49 50                 //取消refresh操作, 重置active标志. 51                 cancelRefresh(ex);52 53                 // Propagate exception to caller.54                 throw ex;55             }56 57             finally {58                 //重置Spring的核心缓存59                 resetCommonCaches();60             }61         }62     }

5.刷新完上下文后

spring boot提供的2个供用户自己拓展的接口：ApplicationRunner和CommandLineRunner。可以在容器启动完毕后（上下文刷新后）执行，做一些类似数据初始化的操作。

 1 private void callRunners(ApplicationContext context, ApplicationArguments args) { 2         List<Object> runners = new ArrayList<Object>(); 3         runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());//从上下文中获取ApplicationRunner类型的bean 4         runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());//从上下文中获取CommandLineRunner类型的bean 5         AnnotationAwareOrderComparator.sort(runners);//排序 6         for (Object runner : new LinkedHashSet<Object>(runners)) { 7             if (runner instanceof ApplicationRunner) { 8                 callRunner((ApplicationRunner) runner, args);//执行 9             }10             if (runner instanceof CommandLineRunner) {11                 callRunner((CommandLineRunner) runner, args);12             }13         }14     }

两个区别在于入参不同，根据实际情况自己选择。

 1 public interface CommandLineRunner { 8     void run(String... args) throws Exception;10 }11 12 public interface ApplicationRunner {19     void run(ApplicationArguments args) throws Exception;20 21 }

CommandLineRunner中执行参数是原始的java启动类main方法的String[] args字符串数组参数；ApplicationRunner中的参数经过处理提供一些方法例如:

1 List<String> getOptionValues(String name);

根据名称获取值list,java 启动命令中 --foo=bar --foo=baz，则根据foo参数名返回list["bar", "baz"]

回到顶部

三、总结

按照前面的分析，Spring-boot容器启动流程总体可划分为2部分：

1）执行注解：扫描指定范围下的bean、载入自动配置类对应的bean加载到IOC容器。

2）man方法中具体SpringAppliocation.run()，全流程贯穿SpringApplicationEvent,有6个子类：

ApplicationEnvironmentPreparedEvent

ApplicationFailedEvent.class

ApplicationPreparedEvent.class

ApplicationReadyEvent.class

ApplicationStartedEvent.class

ApplicationStartingEvent.class

这里用到了很经典的spring事件驱动模型，飞机票：Spring事件驱动模型和观察者模式

类图如下：

如上图，就是一个经典spring 事件驱动模型，包含3种角色：事件发布者、事件、监听者。对应到spring-boot中就是：

1.EventPublishingRunListener这个类封装了事件发布，

2.SpringApplicationEvent是spring-boot中定义的事件（上面说的6种事件），继承自ApplicationEvent（spring中定义的）

3.ApplicationListener<E extends ApplicationEvent> 是spring-boot针对上述6种事件的监听者，这里用户也可以自己实现监听者（上述6种事件）来注入spring boot容器启动流程，触发相应的事件。

例如：实现ApplicationListener<ApplicationReadyEvent>这个接口，在容器启动完毕时最后一步listener.finished时，如果启动没有异常，就会执行！可以做一些数据初始化之类的操作。