Spring源码(十二)：Spring MVC之Spring Boot

本篇将详细讨论Spring Boot 的启动/加载、处理请求的具体流程。我们先从一个简单的Spring Boot项目日志开始分析（这里假设读者已经仔细阅读完了前面的文章，且对Spring源码有一定深度的了解，否则会看得一脸懵逼）。

本文为2024重置版，基于JDK8、Spring Boot 2.2.6.RELEASE（最初版本基于Spring MVC + XML配置，现已废弃去除）。

一、相关代码

1、pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><parent><groupId>site.xiaokui</groupId><artifactId>k-2019</artifactId><version>1.0.0</version></parent><modelVersion>4.0.0</modelVersion><artifactId>k-mini</artifactId><dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency></dependencies>
</project>

2、相关类

@SpringBootApplication
public class MiniAppRunner {public static void main(String[] args) {SpringApplication.run(MiniAppRunner.class, args);}
}

@Slf4j
@RequiredArgsConstructor
@RestController
public class TestController {@PostMapping("/test")@ResponseBodypublic Object test0(@RequestBody Map<String, Object> map) {log.info("前端传来数据:" + map);return map;}
}

POST http://127.0.0.1:7077/test?aa=1&bb=2
Content-Type: application/json{"data": {"login_type": "08","login_str": "abcd"}
}

3、相关配置

debug: trueserver:port: 7077logging:level.root: tracelevel.org.apache.tomcat: infolevel.sun.rmi: info

以上为相关测试代码，读者也可搭建环境自行测试（省略具体输出日志）。

二、SpringApplication

1、构造方法

// main方法入口，来自类 SpringApplication
public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {return run(new Class<?>[] { primarySource }, args);
}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));// 判断当前运行环境，可选 none、servlet、reactivethis.webApplicationType = WebApplicationType.deduceFromClasspath();// 读取 META-INF/spring.factories，加载相关启动类// 加载初始化相关类，共有7个 = 5 + 2，数字刚好与下文的两份 spring.factories对上// 注意这里只是设置，还尚未开始调用setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));// 加载监听器，监听相关事件，共有11个 = 10 + 1setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));// 寻找main方法所在的类作为主类this.mainApplicationClass = deduceMainApplicationClass();
}

2、spring.factories

来自jar包 org.springframework.boot:spring-boot:2.2.6.REALEASE。

# PropertySource Loaders
org.springframework.boot.env.PropertySourceLoader=\
org.springframework.boot.env.PropertiesPropertySourceLoader,\
org.springframework.boot.env.YamlPropertySourceLoader# Run Listeners
org.springframework.boot.SpringApplicationRunListener=\
org.springframework.boot.context.event.EventPublishingRunListener# Error Reporters
org.springframework.boot.SpringBootExceptionReporter=\
org.springframework.boot.diagnostics.FailureAnalyzers# Application Context Initializers，5个
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\
org.springframework.boot.context.ContextIdApplicationContextInitializer,\
org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\
org.springframework.boot.rsocket.context.RSocketPortInfoApplicationContextInitializer,\
org.springframework.boot.web.context.ServerPortInfoApplicationContextInitializer# Application Listeners，10个
org.springframework.context.ApplicationListener=\
org.springframework.boot.ClearCachesApplicationListener,\
org.springframework.boot.builder.ParentContextCloserApplicationListener,\
org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\
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.context.logging.ClasspathLoggingApplicationListener,\
org.springframework.boot.context.logging.LoggingApplicationListener,\
org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener# Environment Post Processors
org.springframework.boot.env.EnvironmentPostProcessor=\
org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\
org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor,\
org.springframework.boot.env.SystemEnvironmentPropertySourceEnvironmentPostProcessor,\
org.springframework.boot.reactor.DebugAgentEnvironmentPostProcessor# Failure Analyzers
org.springframework.boot.diagnostics.FailureAnalyzer=\
org.springframework.boot.diagnostics.analyzer.BeanCurrentlyInCreationFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.BeanDefinitionOverrideFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.BeanNotOfRequiredTypeFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.BindFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.BindValidationFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.UnboundConfigurationPropertyFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.ConnectorStartFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.NoSuchMethodFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.NoUniqueBeanDefinitionFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.PortInUseFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.ValidationExceptionFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.InvalidConfigurationPropertyNameFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.InvalidConfigurationPropertyValueFailureAnalyzer# FailureAnalysisReporters
org.springframework.boot.diagnostics.FailureAnalysisReporter=\
org.springframework.boot.diagnostics.LoggingFailureAnalysisReporter

来自来自jar包 org.springframework.boot:spring-boot-autoconfigure:2.2.6.REALEASE。

# Initializers，2个
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener# Application Listeners，1个
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.OnBeanCondition,\
org.springframework.boot.autoconfigure.condition.OnClassCondition,\
org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition# Auto Configure
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.CloudServiceConnectorsAutoConfiguration,\
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.CassandraReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveRepositoriesAutoConfiguration,\
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.elasticsearch.ReactiveElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveRestClientAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jdbc.JdbcRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveRepositoriesAutoConfiguration,\
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.RedisReactiveAutoConfiguration,\
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.elasticsearch.rest.RestClientAutoConfiguration,\
org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\
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.http.HttpMessageConvertersAutoConfiguration,\
org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,\
org.springframework.boot.autoconfigure.influx.InfluxDbAutoConfiguration,\
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.groovy.template.GroovyTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\
org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\
org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\
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.mongo.embedded.EmbeddedMongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\
org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\
org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketRequesterAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketServerAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketStrategiesAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.UserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.security.rsocket.RSocketSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.saml2.Saml2RelyingPartyAutoConfiguration,\
org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\
org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.servlet.OAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.reactive.ReactiveOAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.resource.servlet.OAuth2ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.resource.reactive.ReactiveOAuth2ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\
org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration,\
org.springframework.boot.autoconfigure.task.TaskSchedulingAutoConfiguration,\
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.client.RestTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.function.client.ClientHttpConnectorAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.reactive.WebSocketReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.client.WebServiceTemplateAutoConfiguration# Failure analyzers
org.springframework.boot.diagnostics.FailureAnalyzer=\
org.springframework.boot.autoconfigure.diagnostics.analyzer.NoSuchBeanDefinitionFailureAnalyzer,\
org.springframework.boot.autoconfigure.flyway.FlywayMigrationScriptMissingFailureAnalyzer,\
org.springframework.boot.autoconfigure.jdbc.DataSourceBeanCreationFailureAnalyzer,\
org.springframework.boot.autoconfigure.jdbc.HikariDriverConfigurationFailureAnalyzer,\
org.springframework.boot.autoconfigure.session.NonUniqueSessionRepositoryFailureAnalyzer# 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.servlet.JspTemplateAvailabilityProvider

3、事件周期图

下图展现SpringApplication的事件全生命周期，读者可以按照此图对照源码进行阅读。其中相关核心类有（断点神类）

SpringApplication
SimpleApplicationEventMulticaster

4、主干

// 主干逻辑
public ConfigurableApplicationContext run(String... args) {// 统计耗时StopWatch stopWatch = new StopWatch();stopWatch.start();// WebApplicationContextConfigurableApplicationContext context = null;Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();// 设置无图形界面服务器工作模式configureHeadlessProperty();SpringApplicationRunListeners listeners = getRunListeners(args);// 触发事件 ApplicationStartingEvent// 分别为 LoggingApplicationListener、BackgroundPreinitializer、DelegatingApplicationListener、LiquibaseServiceLocatorApplicationListener// 这里重点关注下 LoggingApplicationListener、BackgroundPreinitializerlisteners.starting();try {ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);// 准备环境，包含各种系统属性、环境变量、配置值// 触发事件 ApplicationEnvironmentPreparedEventConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);configureIgnoreBeanInfo(environment);Banner printedBanner = printBanner(environment);// 创建 AnnotationConfigServletWebServerApplicationContextcontext = createApplicationContext();exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,new Class[] { ConfigurableApplicationContext.class }, context);// 触发 applyInitializers// 触发事件 ApplicationContextInitializedEvent、ApplicationPreparedEventprepareContext(context, environment, listeners, applicationArguments, printedBanner);// 完成刷新触发事件 ContextRefreshedEvent、ServletWebServerInitializedEventrefreshContext(context);// 空实现，留作扩展afterRefresh(context, applicationArguments// 完成统计耗时stopWatch.stop();if (this.logStartupInfo) {// 打印启动耗时// Started MiniAppRunner in 106.05 seconds (JVM running for 189.145)new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);}// 触发事件 ApplicationStartedEventlisteners.started(context);// 调用 ApplicationRunner、CommandLineRunnercallRunners(context, applicationArguments);}catch (Throwable ex) {handleRunFailure(context, ex, exceptionReporters, listeners);throw new IllegalStateException(ex);}try {// 发布事件 ApplicationReadyEvent，代表Spring已经完全启动了listeners.running(context);}catch (Throwable ex) {handleRunFailure(context, ex, exceptionReporters, null);throw new IllegalStateException(ex);}return context;
}

三、系统属性初始化

1、ApplicationStartingEvent

1、LoggingApplicationListener

// 来自类 LoggingApplicationListener
@Override
public void onApplicationEvent(ApplicationEvent event) {// 系统开始启动事件if (event instanceof ApplicationStartingEvent) {onApplicationStartingEvent((ApplicationStartingEvent) event);}else if (event instanceof ApplicationEnvironmentPreparedEvent) {onApplicationEnvironmentPreparedEvent((ApplicationEnvironmentPreparedEvent) event);}else if (event instanceof ApplicationPreparedEvent) {onApplicationPreparedEvent((ApplicationPreparedEvent) event);}else if (event instanceof ContextClosedEvent&& ((ContextClosedEvent) event).getApplicationContext().getParent() == null) {onContextClosedEvent();}else if (event instanceof ApplicationFailedEvent) {onApplicationFailedEvent();}
}private void onApplicationStartingEvent(ApplicationStartingEvent event) {// 准备 LoggingSystemthis.loggingSystem = LoggingSystem.get(event.getSpringApplication().getClassLoader());// 日志系统初始化之前的准备工作this.loggingSystem.beforeInitialize();
}// 来自类 LoggingSystem
@Override
public void beforeInitialize() {LoggerContext loggerContext = getLoggerContext();if (isAlreadyInitialized(loggerContext)) {return;}// 会触发父类 Slf4JLoggingSystem 的初始化// 此步骤会尽量保证系统只有一个日志框架生效，例如jdklog、logback、log4j只会生效一个super.beforeInitialize();loggerContext.getTurboFilterList().add(FILTER);
}

2、BackgroundPreinitializer

// 来自类 BackgroundPreinitializer
@Override
public void onApplicationEvent(SpringApplicationEvent event) {if (!Boolean.getBoolean(IGNORE_BACKGROUNDPREINITIALIZER_PROPERTY_NAME)&& event instanceof ApplicationStartingEvent && multipleProcessors()&& preinitializationStarted.compareAndSet(false, true)) {performPreinitialization();}if ((event instanceof ApplicationReadyEvent || event instanceof ApplicationFailedEvent)&& preinitializationStarted.get()) {try {preinitializationComplete.await();}catch (InterruptedException ex) {Thread.currentThread().interrupt();}}
}// 主要作用是执行类的预热，因为组件较多，提前异步实例化，可提升系统启动速度
// 实例化好的对象，最终会保存到一个静态对象中，下次直接使用即可
private void performPreinitialization() {try {Thread thread = new Thread(new Runnable() {@Overridepublic void run() {runSafely(new ConversionServiceInitializer());runSafely(new ValidationInitializer());runSafely(new MessageConverterInitializer());runSafely(new JacksonInitializer());runSafely(new CharsetInitializer());preinitializationComplete.countDown();}public void runSafely(Runnable runnable) {try {runnable.run();}catch (Throwable ex) {// Ignore}}}, "background-preinit");thread.start();}catch (Exception ex) {// This will fail on GAE where creating threads is prohibited. We can safely// continue but startup will be slightly slower as the initialization will now// happen on the main thread.preinitializationComplete.countDown();}
}

2、prepareEnvironment

private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,ApplicationArguments applicationArguments) {// Create and configure the environment// 此时具有环境变量和系统属性，但还未有配置文件属性ConfigurableEnvironment environment = getOrCreateEnvironment();configureEnvironment(environment, applicationArguments.getSourceArgs());ConfigurationPropertySources.attach(environment);// 发布环境就绪事件// 会触发监听类 ConfigFileApplicationListener、AnsiOutputApplicationListener、LoggingApplicationListener// ClasspathLoggingApplicationListener、BackgroundPreinitializer、DelegatingApplicationListener、FileEncodingApplicationListenerlisteners.environmentPrepared(environment);bindToSpringApplication(environment);if (!this.isCustomEnvironment) {environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,deduceEnvironmentClass());}ConfigurationPropertySources.attach(environment);return environment;
}

1、getOrCreateEnvironment

private ConfigurableEnvironment getOrCreateEnvironment() {if (this.environment != null) {return this.environment;}switch (this.webApplicationType) {// 走此逻辑case SERVLET:return new StandardServletEnvironment();case REACTIVE:return new StandardReactiveWebEnvironment();default:return new StandardEnvironment();}
}public class StandardServletEnvironment extends StandardEnvironment implements ConfigurableWebEnvironment {}// 会首先触发父类的初始化
public AbstractEnvironment() {// 开始读取配置customizePropertySources(this.propertySources);
}// 来自类 StandardServletEnvironment
@Override
protected void customizePropertySources(MutablePropertySources propertySources) {propertySources.addLast(new StubPropertySource(SERVLET_CONFIG_PROPERTY_SOURCE_NAME));propertySources.addLast(new StubPropertySource(SERVLET_CONTEXT_PROPERTY_SOURCE_NAME));if (JndiLocatorDelegate.isDefaultJndiEnvironmentAvailable()) {propertySources.addLast(new JndiPropertySource(JNDI_PROPERTY_SOURCE_NAME));}// 回调父类 customizePropertySourcessuper.customizePropertySources(propertySources);
}// 来自类 StandardEnvironment
@Override
protected void customizePropertySources(MutablePropertySources propertySources) {// 底层为 (Map) System.getProperties()propertySources.addLast(new PropertiesPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));// 底层为 (Map) System.getenv()propertySources.addLast(new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment()));
}

2、ApplicationEnvironmentPreparedEvent

限于篇幅，这里不详细展开，大概列下：

ConfigFileApplicationListener：用于加载外部配置文件。
AnsiOutputApplicationListener：让你的终端（可以是控制台、可以是日志文件）支持Ansi彩色输出。
LoggingApplicationListener：初始化日志系统。
ClasspathLoggingApplicationListener：用于把classpath路径以log.debug()输出。
BackgroundPreinitializer：无动作。
DelegatingApplicationListener：执行通过外部化配置context.listener.classes = xxx,xxx的监听器们，然后把该事件广播给他们。
FileEncodingApplicationListener：检查文件编码file.encoding。

ConfigFileApplicationListener 部分关键代码如下

// 来自类 ConfigFileApplicationListener
@Override
public void onApplicationEvent(ApplicationEvent event) {if (event instanceof ApplicationEnvironmentPreparedEvent) {onApplicationEnvironmentPreparedEvent((ApplicationEnvironmentPreparedEvent) event);}if (event instanceof ApplicationPreparedEvent) {onApplicationPreparedEvent(event);}
}private void onApplicationEnvironmentPreparedEvent(ApplicationEnvironmentPreparedEvent event) {// 分别为 SystemEnvironmentPropertySourceEnvironmentPostProcessor、SpringApplicationJsonEnvironmentPostProcessor// CloudFoundryVcapEnvironmentPostProcessor、DebugAgentEnvironmentPostProcessorList<EnvironmentPostProcessor> postProcessors = loadPostProcessors();// 注意 add this了// 读取外部配置，这个最重要的活是自己来干postProcessors.add(this);AnnotationAwareOrderComparator.sort(postProcessors);for (EnvironmentPostProcessor postProcessor : postProcessors) {postProcessor.postProcessEnvironment(event.getEnvironment(), event.getSpringApplication());}
}// 来自类 ConfigFileApplicationListener
@Override
public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) {addPropertySources(environment, application.getResourceLoader());
}// 鉴于代码较多，这里只列举部分关键代码
// 默认配置文件路径 DEFAULT_SEARCH_LOCATIONS = "classpath:/,classpath:/config/,file:./,file:./config/";
private void load(Profile profile, DocumentFilterFactory filterFactory, DocumentConsumer consumer) {getSearchLocations().forEach((location) -> {boolean isFolder = location.endsWith("/");Set<String> names = isFolder ? getSearchNames() : NO_SEARCH_NAMES;names.forEach((name) -> load(location, name, profile, filterFactory, consumer));});
}

LoggingApplicationListener 部分关键代码如下

// 来自类 LoggingApplicationListener
private void onApplicationEnvironmentPreparedEvent(ApplicationEnvironmentPreparedEvent event) {// 上一事件已经完成准备工作if (this.loggingSystem == null) {this.loggingSystem = LoggingSystem.get(event.getSpringApplication().getClassLoader());}// 直接跳到这里开始初始化initialize(event.getEnvironment(), event.getSpringApplication().getClassLoader());
}protected void initialize(ConfigurableEnvironment environment, ClassLoader classLoader) {// 设置日志属性默认值new LoggingSystemProperties(environment).apply();// 日志文件名 logging.file.name、logging.file// 日志文件路径 logging.file.path、logging.paththis.logFile = LogFile.get(environment);if (this.logFile != null) {this.logFile.applyToSystemProperties();}// 默认logger web & sqlthis.loggerGroups = new LoggerGroups(DEFAULT_GROUP_LOGGERS);// 设置early日志级别，主要是 debug/trace = true/falseinitializeEarlyLoggingLevel(environment);// 根据日志配置，初始化日志系统，包括 日志输出格式、日志存放路径、日志存放策略等initializeSystem(environment, this.loggingSystem, this.logFile);// 设置日志级别，含root和各个子包路径initializeFinalLoggingLevels(environment, this.loggingSystem);// 注册销毁钩子registerShutdownHookIfNecessary(environment, this.loggingSystem);
}

3、printBanner

打印banner，关键类为 SpringApplicationBannerPrinter，这里不做详细展开。

// 只列举部分字段
class SpringApplicationBannerPrinter {static final String BANNER_LOCATION_PROPERTY = "spring.banner.location";static final String BANNER_IMAGE_LOCATION_PROPERTY = "spring.banner.image.location";static final String DEFAULT_BANNER_LOCATION = "banner.txt";static final String[] IMAGE_EXTENSION = { "gif", "jpg", "png" };// 默认打印 spring boot 版本信息private static final Banner DEFAULT_BANNER = new SpringBootBanner();private final ResourceLoader resourceLoader;private final Banner fallbackBanner;// 其他略
}

四、WebApplication初始化

1、createApplicationContext

// 来自类 SpringApplication
protected ConfigurableApplicationContext createApplicationContext() {Class<?> contextClass = this.applicationContextClass;if (contextClass == null) {try {switch (this.webApplicationType) {case SERVLET:// 走此逻辑，类为 AnnotationConfigServletWebServerApplicationContextcontextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);break;case REACTIVE:// AnnotationConfigReactiveWebServerApplicationContextcontextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);break;default:// AnnotationConfigApplicationContext     contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);}}catch (ClassNotFoundException ex) {throw new IllegalStateException("Unable create a default ApplicationContext, please specify an ApplicationContextClass", ex);}}return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}

2、prepareContext

private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment,SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {context.setEnvironment(environment);postProcessApplicationContext(context);// 触发初始化逻辑，共7个，具体参见前文applyInitializers(context);// 发布事件 ApplicationContextInitializedEventlisteners.contextPrepared(context);if (this.logStartupInfo) {logStartupInfo(context.getParent() == null);logStartupProfileInfo(context);}// Add boot specific singleton beansConfigurableListableBeanFactory beanFactory = context.getBeanFactory();beanFactory.registerSingleton("springApplicationArguments", applicationArguments);if (printedBanner != null) {beanFactory.registerSingleton("springBootBanner", printedBanner);}if (beanFactory instanceof DefaultListableBeanFactory) {((DefaultListableBeanFactory) beanFactory).setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);}if (this.lazyInitialization) {context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());}// Load the sourcesSet<Object> sources = getAllSources();Assert.notEmpty(sources, "Sources must not be empty");load(context, sources.toArray(new Object[0]));// 发布 ApplicationPreparedEventlisteners.contextLoaded(context);
}

1、applyInitializers

// 触发相关类为 DelegatingApplicationContextInitializer、SharedMetadataReaderFactoryContextInitializer、ContextIdApplicationContextInitializer
// ConfigurationWarningsApplicationContextInitializer、RSocketPortInfoApplicationContextInitializer
// ServerPortInfoApplicationContextInitializer、ConditionEvaluationReportLoggingListener
protected void applyInitializers(ConfigurableApplicationContext context) {for (ApplicationContextInitializer initializer : getInitializers()) {Class<?> requiredType = GenericTypeResolver.resolveTypeArgument(initializer.getClass(),ApplicationContextInitializer.class);Assert.isInstanceOf(requiredType, context, "Unable to call initializer.");initializer.initialize(context);}
}

2、contextPrepared

// 来自类 SpringApplicationRunListeners
// 发布WebApplication就绪事件
void contextPrepared(ConfigurableApplicationContext context) {for (SpringApplicationRunListener listener : this.listeners) {listener.contextPrepared(context);}
}// 来自类 EventPublishingRunListener
@Override
public void contextPrepared(ConfigurableApplicationContext context) {this.initialMulticaster.multicastEvent(new ApplicationContextInitializedEvent(this.application, this.args, context));
}

3、contextLoaded

// 来自类 SpringApplicationRunListeners
// 发布WebApplication加载完毕事件
void contextLoaded(ConfigurableApplicationContext context) {for (SpringApplicationRunListener listener : this.listeners) {listener.contextLoaded(context);}
}// 来自类 EventPublishingRunListener
@Override
public void contextLoaded(ConfigurableApplicationContext context) {for (ApplicationListener<?> listener : this.application.getListeners()) {if (listener instanceof ApplicationContextAware) {((ApplicationContextAware) listener).setApplicationContext(context);}context.addApplicationListener(listener);}this.initialMulticaster.multicastEvent(new ApplicationPreparedEvent(this.application, this.args, context));
}

3、refreshContext

// 来自类 SpringApplication
private void refreshContext(ConfigurableApplicationContext context) {refresh(context);if (this.registerShutdownHook) {try {context.registerShutdownHook();}catch (AccessControlException ex) {// Not allowed in some environments.}}
}protected void refresh(ApplicationContext applicationContext) {Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);// 触发上下文的刷新动作// 这里不做过多展开，具体请参见前文((AbstractApplicationContext) applicationContext).refresh();
}public Collection<ApplicationListener<?>> getApplicationListeners() {return this.applicationListeners;
}// 来自类 AbstractApplicationContext
@Override
public void refresh() throws BeansException, IllegalStateException {synchronized (this.startupShutdownMonitor) {// Prepare this context for refreshing.prepareRefresh();// Tell the subclass to refresh the internal bean factory.ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();// Prepare the bean factory for use in this context.prepareBeanFactory(beanFactory);try {// Allows post-processing of the bean factory in context subclasses.postProcessBeanFactory(beanFactory);// Invoke factory processors registered as beans in the context.invokeBeanFactoryPostProcessors(beanFactory);// Register bean processors that intercept bean creation.registerBeanPostProcessors(beanFactory);// Initialize message source for this context.initMessageSource();// Initialize event multicaster for this context.initApplicationEventMulticaster();// Initialize other special beans in specific context subclasses.onRefresh();// Check for listener beans and register them.registerListeners();// Instantiate all remaining (non-lazy-init) singletons.finishBeanFactoryInitialization(beanFactory);// Last step: publish corresponding event.// 发布 ContextRefreshedEvent、ServletWebServerInitializedEvent 事件// 会有一次 super.finishRefreshfinishRefresh();}catch (BeansException ex) {if (logger.isWarnEnabled()) {logger.warn("Exception encountered during context initialization - " +"cancelling refresh attempt: " + ex);}// Destroy already created singletons to avoid dangling resources.destroyBeans();// Reset 'active' flag.cancelRefresh(ex);// Propagate exception to caller.throw ex;}finally {// Reset common introspection caches in Spring's core, since we// might not ever need metadata for singleton beans anymore...resetCommonCaches();}}
}

刷新完后的 AnnotationConfigServletWebServerApplicationContext 将完全具有 BeanFactory 和 ApplicationContext 的功能，剩下的就是一些收尾工作。

在完成刷新之后，会发布 ContextRefreshedEvent、ServletWebServerInitializedEvent 事件。

4、callRunners

我们可以在Spring完全启动后，通过实现 ApplicationRunner、CommandLineRunner 接口做一些事情。

private void callRunners(ApplicationContext context, ApplicationArguments args) {List<Object> runners = new ArrayList<>();runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());AnnotationAwareOrderComparator.sort(runners);for (Object runner : new LinkedHashSet<>(runners)) {if (runner instanceof ApplicationRunner) {callRunner((ApplicationRunner) runner, args);}if (runner instanceof CommandLineRunner) {callRunner((CommandLineRunner) runner, args);}}
}