目錄
一、前言
spring cloud大行其道的當下，如果不瞭解基本原理那麼是很糾結的(看見的都是約定大於配置，但是原理呢？爲什麼要這麼做？如何串聯起來的？)。spring cloud是基於spring boot快速搭建的，今天咱們就看看spring boot容器啓動流程(全文基於1.5.9版本)。(本文不講解如何快速啓動spring boot，那些直接官方看即可)
二、容器啓動
spring boot一般是指定容器啓動main方法，然後以命令行方式啓動Jar包，如下圖：
1 @SpringBootApplication
2 public class Application {
3 public static void main(String[] args) {
4 SpringApplication.run(Application.class, args);
5 }
6 }
這裏核心關注2個東西：
下面我們就分別探究這兩塊內容。
2.1 @SpringBootApplication註解
源碼如下：
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 {
核心註解：
@SpringBootConfiguration（實際就是個@Configuration）：表示這是一個JavaConfig配置類，可以在這個類中自定義bean,依賴關係等。-》這個是spring-boot特有的註解，常用到。 @EnableAutoConfiguration：藉助@Import的幫助，將所有符合自動配置條件的bean定義加載到IoC容器（建議放在根包路徑下，這樣可以掃描子包和類）。-》這個需要詳細深挖！ @ComponentScan：spring的自動掃描註解，可定義掃描範圍，加載到IOC容器。-》這個不多說，spring的註解大家肯定眼熟 其中@EnableAutoConfiguration這個註解的源碼：
1 @SuppressWarnings("deprecation")
2 @Target(ElementType.TYPE)
3 @Retention(RetentionPolicy.RUNTIME)
4 @Documented
5 @Inherited
6 @AutoConfigurationPackage
7 @Import(EnableAutoConfigurationImportSelector.class)
8 public @interface EnableAutoConfiguration {
核心是一個EnableAutoConfigurationImportSelector類圖如下：
核心方法在頂級接口ImportSelector的selectImports（），源碼如下：
1 @Override
2 public String[] selectImports(AnnotationMetadata annotationMetadata) {
3 if (!isEnabled(annotationMetadata)) {
4 return NO_IMPORTS;
5 }
6 try { //1.從META-INF/spring-autoconfigure-metadata.properties文件中載入483條配置屬性（有一些有默認值），
7 AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
8 .loadMetadata(this.beanClassLoader);
9 AnnotationAttributes attributes = getAttributes(annotationMetadata);//2.獲取註解屬性
10 List<String> configurations = getCandidateConfigurations(annotationMetadata,//3.獲取97個自動配置類
11 attributes);
12 configurations = removeDuplicates(configurations);//4.移除重複的
13 configurations = sort(configurations, autoConfigurationMetadata);//5.排序
14 Set<String> exclusions = getExclusions(annotationMetadata, attributes);//6.獲取需要排除的
15 checkExcludedClasses(configurations, exclusions);//7.校驗排除類
16 configurations.removeAll(exclusions);//8.刪除所有需要排除的
17 configurations = filter(configurations, autoConfigurationMetadata);//9.過濾器OnClassCondition（註解中配置的當存在某類才生效）
18 fireAutoConfigurationImportEvents(configurations, exclusions);//10.觸發自動配置導入監聽事件
19 return configurations.toArray(new String[configurations.size()]);
20 }
21 catch (IOException ex) {
22 throw new IllegalStateException(ex);
23 }
24 }
這裏注意3個核心方法：
1）loadMetadata 加載配置
其實就是用類加載器去加載：META-INF/spring-autoconfigure-metadata.properties（spring-boot-autoconfigure-1.5.9.RELEASE-sources.jar）文件中定義的配置，返回PropertiesAutoConfigurationMetadata（實現了AutoConfigurationMetadata接口，封裝了屬性的get set方法）
2）getCandidateConfigurations獲取默認支持的自動配置類名列表
自動配置靈魂方法，SpringFactoriesLoader.loadFactoryNames 從META-INF/spring.factories（spring-boot-autoconfigure-1.5.9.RELEASE-sources.jar）文件中獲取自動配置類key=EnableAutoConfiguration.class的配置。
1 protected List<String> getCandidateConfigurations(AnnotationMetadata metadata,
2 AnnotationAttributes attributes) {//話說這裏2個入參沒啥用啊...誰來給我解釋一下...
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類
11 protected Class<?> getSpringFactoriesLoaderFactoryClass() {
12 return EnableAutoConfiguration.class;
13 }
實際獲取了什麼？spring.factories文件如下，實際獲取了# Auto Configure自動配置模塊的所有類。
# Initializers org.springframework.context.ApplicationContextInitializer=\ org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\ org.springframework.boot.autoconfigure.logging.AutoConfigurationReportLoggingInitializer # Application Listeners org.springframework.context.ApplicationListener=\ org.springframework.boot.autoconfigure.BackgroundPreinitializer # Auto Configuration Import Listeners org.springframework.boot.autoconfigure.AutoConfigurationImportListener=\ org.springframework.boot.autoconfigure.condition.ConditionEvaluationReportAutoConfigurationImportListener # Auto Configuration Import Filters org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\ org.springframework.boot.autoconfigure.condition.OnClassCondition # Auto Configure ===========這裏就是全部的自動配置類=============================== 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 analyzers org.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 providers org.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過濾器 根據OnClassCondition註解把不滿足條件的過濾掉
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;
//獲取需要過濾的自動配置導入攔截器，spring.factories配置中就一個：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) {//多條件只要有一個不匹配->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-》不跳過-》添加進result
23 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 }
2.2 SpringApplication.run()靜態方法
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.獲取監聽器
8 listeners.starting();-->啓動！
9 try {
10 ApplicationArguments applicationArguments = new DefaultApplicationArguments(
11 args);
12 ConfigurableEnvironment environment = prepareEnvironment(listeners,//2.準備好環境，觸發ApplicationEnvironmentPreparedEvent事件
13 applicationArguments);
14 Banner printedBanner = printBanner(environment);//打印啓動提示字符，默認spring的字符圖
15 context = createApplicationContext();//實例化一個可配置應用上下文
16 analyzers = new FailureAnalyzers(context);
17 prepareContext(context, environment, listeners, applicationArguments,//3.準備上下文
18 printedBanner);
19 refreshContext(context);//4.刷新上下文
20 afterRefresh(context, applicationArguments);//5.刷新上下文後
21 listeners.finished(context, null);--關閉！
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 }
如上圖,容器啓動流程可以分爲5個主要步驟：
1.getRunListeners獲取監聽器（SpringApplicationRunListeners ）
實際是SpringApplicationRunListener類
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確保的字符串的唯一性
15 Set<String> names = new LinkedHashSet<String>(
16 SpringFactoriesLoader.loadFactoryNames(type, classLoader));// 1.載入工廠名稱集合
17 List<T> instances = createSpringFactoriesInstances(type, parameterTypes,// 2.創建工廠實例
18 classLoader, args, names);
19 AnnotationAwareOrderComparator.sort(instances);// 排序
20 return instances;
21 }
載入工廠名稱（loadFactoryNames）
當前類的類加載器從META-INF/spring.factories文件中獲取SpringApplicationRunListener類的配置
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 }
上圖，獲取到工廠類名後，下面來看看META-INF/spring.factories中定義了啥：
# PropertySource Loaders org.springframework.boot.env.PropertySourceLoader=\ org.springframework.boot.env.PropertiesPropertySourceLoader,\ org.springframework.boot.env.YamlPropertySourceLoader # Run Listeners 這裏呢，看這裏！！！！ org.springframework.boot.SpringApplicationRunListener=\ org.springframework.boot.context.event.EventPublishingRunListener # Application Context Initializers org.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 Listeners org.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 Processors org.springframework.boot.env.EnvironmentPostProcessor=\ org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\ org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor # Failure Analyzers org.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 # FailureAnalysisReporters org.springframework.boot.diagnostics.FailureAnalysisReporter=\ org.springframework.boot.diagnostics.LoggingFailureAnalysisReporter
哇，都是些類全名稱，且key都是接口，value都是實現類。我們根據key=“org.springframework.boot.SpringApplicationRunListener”查詢得到實現類value="org.springframework.boot.context.event.EventPublishingRunListener"事件發佈啓動監聽器，一猜也知道肯定要用”反射”根據類名獲取類實例，下面很快得到驗證...
創建spring工廠實例（createSpringFactoriesInstances）
根據第一步得到的Set<String> names（SpringApplicationRunListener的唯一實現類EventPublishingRunListener）生成"事件發佈啓動監聽器"工廠實例
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);// 利用反射獲取類
9 Assert.isAssignable(type, instanceClass);
10 Constructor<?> constructor = instanceClass
11 .getDeclaredConstructor(parameterTypes);// 得到構造器
12 T instance = (T) BeanUtils.instantiateClass(constructor, args);// 根據構造器和參數構造實例
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.準備好環境
構造一個ConfigurableEnvironment,這裏不多說。
3.準備上下文
1 private void prepareContext(ConfigurableApplicationContext context,
2 ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
3 ApplicationArguments applicationArguments, Banner printedBanner) {
4 context.setEnvironment(environment);
5 postProcessApplicationContext(context);//單例一個BeanNameGenerator，把ResourceLoader設置進應用上下文
6 applyInitializers(context);//執行初始化器
7 listeners.contextPrepared(context);// 監聽器執行上下文"已準備好"方法
8 if (this.logStartupInfo) {
9 logStartupInfo(context.getParent() == null);
10 logStartupProfileInfo(context);
11 }
12
13 // 添加spring boot特殊單例bean
14 context.getBeanFactory().registerSingleton("springApplicationArguments",
15 applicationArguments);
16 if (printedBanner != null) {
17 context.getBeanFactory().registerSingleton("springBootBanner", printedBanner);
18 }
19
20 // 載入資源
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);// 監聽器執行"上下文已加載"方法
25 }
4.刷新上下文
1 private void refreshContext(ConfigurableApplicationContext context) {
2 refresh(context);//核心類
3 if (this.registerShutdownHook) {
4 try {
5 context.registerShutdownHook();//註冊關閉鉤子，容器關閉時執行
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 }
最終執行的是AbstractApplicationContext抽象類的refresh方法。
1 public void refresh() throws BeansException, IllegalStateException {
2 synchronized (this.startupShutdownMonitor) {
3 //準備刷新的上下文環境，例如對系統屬性或者環境變量進行準備及驗證。
4 prepareRefresh();
5
6 //啓動子類的refreshBeanFactory方法.解析xml
7 ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
8
9 //爲BeanFactory配置容器特性，例如類加載器、事件處理器等.
10 prepareBeanFactory(beanFactory);
11
12 try {
13 //設置BeanFactory的後置處理. 空方法，留給子類拓展用。
14 postProcessBeanFactory(beanFactory);
15
16 //調用BeanFactory的後處理器, 這些後處理器是在Bean定義中向容器註冊的.
17 invokeBeanFactoryPostProcessors(beanFactory);
18
19 //註冊Bean的後處理器, 在Bean創建過程中調用.
20 registerBeanPostProcessors(beanFactory);
21
22 //初始化上下文中的消息源，即不同語言的消息體進行國際化處理
23 initMessageSource();
24
25 //初始化ApplicationEventMulticaster bean,應用事件廣播器
26 initApplicationEventMulticaster();
27
28 //初始化其它特殊的Bean， 空方法，留給子類拓展用。
29 onRefresh();
30
31 //檢查並向容器註冊監聽器Bean
32 registerListeners();
33
34 //實例化所有剩餘的(non-lazy-init) 單例Bean.
35 finishBeanFactoryInitialization(beanFactory);
36
37 //發佈容器事件, 結束refresh過程.
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 //銷燬已經創建的單例Bean, 以避免資源佔用.
48 destroyBeans();
49
50 //取消refresh操作, 重置active標誌.
51 cancelRefresh(ex);
52
53 // Propagate exception to caller.
54 throw ex;
55 }
56
57 finally {
58 //重置Spring的核心緩存
59 resetCommonCaches();
60 }
61 }
62 }
5.刷新完上下文後
spring boot提供的2個供用戶自己拓展的接口：ApplicationRunner和CommandLineRunner。可以在容器啓動完畢後（上下文刷新後）執行，做一些類似數據初始化的操作。
1 private void callRunners(ApplicationContext context, ApplicationArguments args) {
2 List<Object> runners = new ArrayList<Object>();
3 runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());//從上下文中獲取ApplicationRunner類型的bean
4 runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());//從上下文中獲取CommandLineRunner類型的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);//執行
9 }
10 if (runner instanceof CommandLineRunner) {
11 callRunner((CommandLineRunner) runner, args);
12 }
13 }
14 }
兩個區別在於入參不同，根據實際情況自己選擇。
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中執行參數是原始的java啓動類main方法的String[] args字符串數組參數；ApplicationRunner中的參數經過處理提供一些方法例如:
1 List<String> getOptionValues(String name);
根據名稱獲取值list,java 啓動命令中 --foo=bar --foo=baz，則根據foo參數名返回list["bar", "baz"]
三、總結
按照前面的分析，Spring-boot容器啓動流程總體可劃分爲2部分：
1）執行註解：掃描指定範圍下的bean、載入自動配置類對應的bean加載到IOC容器。
2）man方法中具體SpringAppliocation.run()，全流程貫穿SpringApplicationEvent,有6個子類：
ApplicationFailedEvent.class
ApplicationPreparedEvent.class
ApplicationReadyEvent.class
ApplicationStartedEvent.class
ApplicationStartingEvent.class
SpringApplicationEvent.class
這裏用到了很經典的spring事件驅動模型，飛機票：Spring事件驅動模型和觀察者模式
類圖如下：
如上圖，就是一個經典spring 事件驅動模型，包含3種角色：事件發佈者、事件、監聽者。對應到spring-boot中就是：
1.EventPublishingRunListener這個類封裝了事件發佈，
2.SpringApplicationEvent是spring-boot中定義的事件（上面說的6種事件），繼承自ApplicationEvent（spring中定義的）
3.監聽者 spring-boot並沒有實現針對上述6種事件的監聽者（我沒找到...），這裏用戶可以自己實現監聽者（上述6種事件）來注入spring boot容器啓動流程，觸發相應的事件。
例如：實現ApplicationListener<ApplicationReadyEvent>這個接口，在容器啓動完畢時最後一步listener.finished時，如果啓動沒有異常，就會執行！可以做一些數據初始化之類的操作。