SpringBoot源碼分析之---SpringBoot項目啟動類SpringApplication淺析

源碼版本說明

本文源碼采用版本為SpringBoot 2.1.0BUILD,對應(yīng)的SpringFramework 5.1.0.RC1

注意：本文只是從整體上梳理流程巍杈，不做具體深入分析

SpringBoot入口類

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

這是我們?nèi)粘Ｊ褂胹pringboot開發(fā)見到次數(shù)最多的引導(dǎo)類了屡拨，完成這個類的編寫萨醒，就完成了一個springboot項目的框架昔脯，springboot就回自動為我們完成一些默認配置，并幫我們初始化上下文容器刀荒，但細節(jié)我們是不知道的明肮，下面我們就一起探索下SpringApplication.run(DemoApplication .class, args);這行代碼背后的故事！

SpringApplication初始化階段

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

// 初始化準備階段
@SuppressWarnings({ "unchecked", "rawtypes" })
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
    this.resourceLoader = resourceLoader;
    Assert.notNull(primarySources, "PrimarySources must not be null");
    // 參數(shù)初始化
    this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
    // 推斷應(yīng)用類型
    this.webApplicationType = deduceWebApplicationType();
    // 加載ApplicationContextInitializer系列初始化器（從spring.factories文件加載簸州，并實例化和排序后存到this.initializers）
    setInitializers((Collection) getSpringFactoriesInstances(
            ApplicationContextInitializer.class));
    // 加載ApplicationListener系列監(jiān)聽器（從spring.factories文件加載鉴竭，并實例化和排序后存到this.listeners）
    setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
    // 推斷應(yīng)用入口類（main函數(shù)所在類）
    this.mainApplicationClass = deduceMainApplicationClass();
}

推斷應(yīng)用類型

// 推斷應(yīng)用類型
this.webApplicationType = deduceWebApplicationType();

private WebApplicationType deduceWebApplicationType() {
    if (ClassUtils.isPresent(REACTIVE_WEB_ENVIRONMENT_CLASS, null)
            && !ClassUtils.isPresent(MVC_WEB_ENVIRONMENT_CLASS, null)
            && !ClassUtils.isPresent(JERSEY_WEB_ENVIRONMENT_CLASS, null)) {
        return WebApplicationType.REACTIVE;
    }
    for (String className : WEB_ENVIRONMENT_CLASSES) {
        if (!ClassUtils.isPresent(className, null)) {
            return WebApplicationType.NONE;
        }
    }
    return WebApplicationType.SERVLET;
}

private static final String REACTIVE_WEB_ENVIRONMENT_CLASS = "org.springframework."
        + "web.reactive.DispatcherHandler";

private static final String MVC_WEB_ENVIRONMENT_CLASS = "org.springframework."
        + "web.servlet.DispatcherServlet";

private static final String JERSEY_WEB_ENVIRONMENT_CLASS = "org.glassfish.jersey.server.ResourceConfig";

private static final String[] WEB_ENVIRONMENT_CLASSES = { "javax.servlet.Servlet",
        "org.springframework.web.context.ConfigurableWebApplicationContext" };

根據(jù)當(dāng)前應(yīng)用ClassPath下是否存在相關(guān)類，來確定應(yīng)用類型岸浑。

加載`ApplicationContextInitializer`系列初始化器

// 加載ApplicationContextInitializer系列初始化器（從spring.factories文件加載搏存，并實例化和排序后存到this.initializers）
setInitializers((Collection) getSpringFactoriesInstances(
        ApplicationContextInitializer.class));

public void setInitializers(
        Collection<? extends ApplicationContextInitializer<?>> initializers) {
    this.initializers = new ArrayList<>();
    this.initializers.addAll(initializers);
}

private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {
    return getSpringFactoriesInstances(type, new Class<?>[] {});
}

private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
        Class<?>[] parameterTypes, Object... args) {
    ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
    // Use names and ensure unique to protect against duplicates
    Set<String> names = new LinkedHashSet<>(
            SpringFactoriesLoader.loadFactoryNames(type, classLoader));
    List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
            classLoader, args, names);
    AnnotationAwareOrderComparator.sort(instances);
    return instances;
}

@SuppressWarnings("unchecked")
private <T> List<T> createSpringFactoriesInstances(Class<T> type,
        Class<?>[] parameterTypes, ClassLoader classLoader, Object[] args,
        Set<String> names) {
    List<T> instances = new ArrayList<>(names.size());
    for (String name : names) {
        try {
            Class<?> instanceClass = ClassUtils.forName(name, classLoader);
            Assert.isAssignable(type, instanceClass);
            Constructor<?> constructor = instanceClass
                    .getDeclaredConstructor(parameterTypes);
            T instance = (T) BeanUtils.instantiateClass(constructor, args);
            instances.add(instance);
        }
        catch (Throwable ex) {
            throw new IllegalArgumentException(
                    "Cannot instantiate " + type + " : " + name, ex);
        }
    }
    return instances;
}

利用Spring工廠加載機制，實例化ApplicationContextInitializer接口的實現(xiàn)類矢洲，被加載的實現(xiàn)類都配置在MATE-INF/spring.factories文件中璧眠，getSpringFactoriesInstances(Class<T> type,Class<?>[] parameterTypes, Object... args)這個方法就負責(zé)加載配置類并實例化和排序后返回，后面監(jiān)聽器、異常收集器和Runner等也是通過這個類實現(xiàn)實例化對應(yīng)實現(xiàn)類的责静。下面是spring-boot-autoconfigure\src\main\resources\META-INF\spring.factories文件的配置內(nèi)容袁滥。

# Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener

# 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
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.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.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.reactor.core.ReactorCoreAutoConfiguration,\
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.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.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.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.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.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

加載ApplicationListener系列監(jiān)聽器

// 加載ApplicationListener系列監(jiān)聽器（從spring.factories文件加載，并實例化和排序后存到this.listeners）
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));

public void setListeners(Collection<? extends ApplicationListener<?>> listeners) {
    this.listeners = new ArrayList<>();
    this.listeners.addAll(listeners);
}

private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {
    return getSpringFactoriesInstances(type, new Class<?>[] {});
}

如上面的初始化器灾螃，ApplicationListener系列監(jiān)聽器也是通過getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args)這個方法完成加載题翻、排序及實例化的，而后存入到this.listeners中腰鬼。

推斷應(yīng)用入口類

// 推斷應(yīng)用入口類（main函數(shù)所在類）
this.mainApplicationClass = deduceMainApplicationClass();

private Class<?> deduceMainApplicationClass() {
    try {
        // 通過new一個運行時異常獲取堆棧信息
        StackTraceElement[] stackTrace = new RuntimeException().getStackTrace();
        for (StackTraceElement stackTraceElement : stackTrace) {
            // 找到main函數(shù)所在的入口類
            if ("main".equals(stackTraceElement.getMethodName())) {
                return Class.forName(stackTraceElement.getClassName());
            }
        }
    }
    catch (ClassNotFoundException ex) {
        // Swallow and continue
    }
    return null;
}

推斷應(yīng)用入口類這部分比較有意思嵌赠，他是通過new了一個運行時異常來拿到main線程的堆棧信息，遍歷所有方法找到main方法所在的類垃喊。

運行階段

// 運行階段
public ConfigurableApplicationContext run(String... args) {
    // 初始化容器啟動計時器
    StopWatch stopWatch = new StopWatch();
    // 開始計時
    stopWatch.start();
    // 初始化上下文ConfigurableApplicationContext
    ConfigurableApplicationContext context = null;
    // 初始化異常收集器
    Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
    // 配置系統(tǒng)參數(shù)"java.awt.headless"
    configureHeadlessProperty();
    // 獲取SpringApplicationRunListener系列監(jiān)聽器（從spring.factories文件加載猾普，并實例化和排序）
    SpringApplicationRunListeners listeners = getRunListeners(args);
    // 遍歷所有SpringApplicationRunListener系列監(jiān)聽器，廣播ApplicationStartingEvent
    listeners.starting();
    try {
        // 處理args參數(shù)
        ApplicationArguments applicationArguments = new DefaultApplicationArguments(
                args);
        // 準備環(huán)境（創(chuàng)建本谜、配置初家、綁定環(huán)境、廣播ApplicationEnvironmentPreparedEvent）
        ConfigurableEnvironment environment = prepareEnvironment(listeners,
                applicationArguments);
        configureIgnoreBeanInfo(environment);
        // 打印Banner
        Banner printedBanner = printBanner(environment);
        // 根據(jù)應(yīng)用類型創(chuàng)建上下文
        context = createApplicationContext();
        // 獲取SpringBootExceptionReporter系列異常收集器（從spring.factories文件加載乌助，并實例化和排序）
        exceptionReporters = getSpringFactoriesInstances(
                SpringBootExceptionReporter.class,
                new Class[] { ConfigurableApplicationContext.class }, context);
        // 上下文前置處理（執(zhí)行ApplicationContextInitializer系列初始化器溜在、加載資源、廣播ApplicationPreparedEvent）
        prepareContext(context, environment, listeners, applicationArguments,
                printedBanner);
        // 刷新上下文（）
        refreshContext(context);
        // 上下文后置處理(目前啥也沒干)
        afterRefresh(context, applicationArguments);
        // 啟動完成他托，打印用時
        stopWatch.stop();
        if (this.logStartupInfo) {
            new StartupInfoLogger(this.mainApplicationClass)
                    .logStarted(getApplicationLog(), stopWatch);
        }
        // 遍歷前面設(shè)置的ConfigurableApplicationContext監(jiān)聽器掖肋，發(fā)布ApplicationStartedEvent
        listeners.started(context);
        // 按順序回調(diào)實現(xiàn)了ApplicationRunner或CommandLineRunner接口的Runners
        callRunners(context, applicationArguments);
    }
    catch (Throwable ex) {
        // 處理異常（發(fā)布ExitCodeEvent和ApplicationFailedEvent事件、異常收集器處理異常）
        handleRunFailure(context, ex, exceptionReporters, listeners);
        throw new IllegalStateException(ex);
    }

    try {
        // 遍歷前面設(shè)置好的SpringApplicationRunListener監(jiān)聽器赏参，發(fā)布ApplicationReadyEvent
        listeners.running(context);
    }
    catch (Throwable ex) {
        handleRunFailure(context, ex, exceptionReporters, null);
        throw new IllegalStateException(ex);
    }
    return context;
}

獲取`SpringApplicationRunListener`系列監(jiān)聽器

// 獲取SpringApplicationRunListener系列監(jiān)聽器（從spring.factories文件加載志笼，并實例化和排序）
SpringApplicationRunListeners listeners = getRunListeners(args);

private SpringApplicationRunListeners getRunListeners(String[] args) {
    Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };
    return new SpringApplicationRunListeners(logger, getSpringFactoriesInstances(
            SpringApplicationRunListener.class, types, this, args));
}

這里我們再一次見到getSpringFactoriesInstances(Class<T> type,Class<?>[] parameterTypes, Object... args)這個方法，功能同上把篓。

廣播`ApplicationStartingEvent`事件

// 遍歷所有SpringApplicationRunListener系列監(jiān)聽器纫溃，廣播ApplicationStartingEvent
listeners.starting();

public void starting() {
    for (SpringApplicationRunListener listener : this.listeners) {
        listener.starting();
    }
}

public void starting() {
    this.initialMulticaster.multicastEvent(
            new ApplicationStartingEvent(this.application, this.args));
}

這里會遍歷上面拿到的排序好的所有SpringApplicationRunListener系列監(jiān)聽器，廣播ApplicationStartingEvent事件韧掩，這代表Spring應(yīng)用開始啟動紊浩，在這之前只進行了注冊化初始化器和監(jiān)聽器。

準備環(huán)境疗锐、廣播`ApplicationEnvironmentPreparedEvent`事件

// 準備環(huán)境（創(chuàng)建坊谁、配置、綁定環(huán)境滑臊、廣播ApplicationEnvironmentPreparedEvent）
ConfigurableEnvironment environment = prepareEnvironment(listeners,
        applicationArguments);

private ConfigurableEnvironment prepareEnvironment(
        SpringApplicationRunListeners listeners,
        ApplicationArguments applicationArguments) {
    // Create and configure the environment
    ConfigurableEnvironment environment = getOrCreateEnvironment();
    configureEnvironment(environment, applicationArguments.getSourceArgs());
    listeners.environmentPrepared(environment);
    bindToSpringApplication(environment);
    if (this.webApplicationType == WebApplicationType.NONE) {
        environment = new EnvironmentConverter(getClassLoader())
                .convertToStandardEnvironmentIfNecessary(environment);
    }
    ConfigurationPropertySources.attach(environment);
    return environment;
}

public void environmentPrepared(ConfigurableEnvironment environment) {
    for (SpringApplicationRunListener listener : this.listeners) {
        listener.environmentPrepared(environment);
    }
}

@Override
public void environmentPrepared(ConfigurableEnvironment environment) {
    this.initialMulticaster.multicastEvent(new ApplicationEnvironmentPreparedEvent(
            this.application, this.args, environment));
}

這里開始創(chuàng)建口芍、配置和綁定ConfigurableEnvironment環(huán)境，環(huán)境準備好之后開始遍歷SpringApplicationRunListener系列監(jiān)聽器雇卷，廣播ApplicationEnvironmentPreparedEvent事件阶界，代表環(huán)境已準備好虹钮。

開始打印Banner

// 打印Banner
Banner printedBanner = printBanner(environment);

private Banner printBanner(ConfigurableEnvironment environment) {
    // Mode.OFF：不打印banner
    if (this.bannerMode == Banner.Mode.OFF) {
        return null;
    }
    // 加載banner資源聋庵，如果自定義了banner樣式膘融，在這里加載，否則加載默認banner
    ResourceLoader resourceLoader = (this.resourceLoader != null)
            ? this.resourceLoader : new DefaultResourceLoader(getClassLoader());
    // 初始化bannerPrinter
    SpringApplicationBannerPrinter bannerPrinter = new SpringApplicationBannerPrinter(
            resourceLoader, this.banner);
    // Mode.LOG：通過日志打印banner
    if (this.bannerMode == Mode.LOG) {
        return bannerPrinter.print(environment, this.mainApplicationClass, logger);
    }
    // 默認通過控制臺打印banner
    return bannerPrinter.print(environment, this.mainApplicationClass, System.out);
}

關(guān)于Banner祭玉，SpringBoot支持關(guān)閉banner打印氧映、打印到log日志和打印到system日志三種方式；同時支持自定義banner脱货，自定義banner又有圖片和txt文本兩種（同時存在時先打印圖片banner岛都，在打印文本banner），圖片banner又支持gif, jpg, png這三種類型的圖片格式banner（git優(yōu)先于jpg優(yōu)先于png）振峻，自定義banner非常簡單臼疫，只需要將banner文件放到classpath:下就好了（resources目錄下），如果存在多個banner文件扣孟，想指定某一個文件烫堤，只需要在application.properties文件加入如下配置就好了，非常方便凤价。

spring.banner.image.location=banner.png
spring.banner.location=banner.txt

根據(jù)應(yīng)用類型創(chuàng)建上下文

// 根據(jù)應(yīng)用類型創(chuàng)建上下文
context = createApplicationContext();

protected ConfigurableApplicationContext createApplicationContext() {
    Class<?> contextClass = this.applicationContextClass;
    if (contextClass == null) {
        try {
            switch (this.webApplicationType) {
            case SERVLET:
                contextClass = Class.forName(DEFAULT_WEB_CONTEXT_CLASS);
                break;
            case REACTIVE:
                contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
                break;
            default:
                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);
}

public static final String DEFAULT_WEB_CONTEXT_CLASS = "org.springframework.boot."
        + "web.servlet.context.AnnotationConfigServletWebServerApplicationContext";

public static final String DEFAULT_REACTIVE_WEB_CONTEXT_CLASS = "org.springframework."
        + "boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext";
        
public static final String DEFAULT_CONTEXT_CLASS = "org.springframework.context."
        + "annotation.AnnotationConfigApplicationContext";

開始創(chuàng)建ConfigurableApplicationContext上下文鸽斟，其中Servlet類型的web應(yīng)用會創(chuàng)建AnnotationConfigServletWebServerApplicationContext類型的上下文，Reactive類型的web應(yīng)用會創(chuàng)建AnnotationConfigReactiveWebServerApplicationContext類型的上下文利诺，非web應(yīng)用會創(chuàng)建AnnotationConfigApplicationContext類型的上下文富蓄。

獲取`SpringBootExceptionReporter`系列異常收集器

// 獲取SpringBootExceptionReporter系列異常收集器（從spring.factories文件加載，并實例化和排序）
exceptionReporters = getSpringFactoriesInstances(
        SpringBootExceptionReporter.class,
        new Class[] { ConfigurableApplicationContext.class }, context);

private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
        Class<?>[] parameterTypes, Object... args) {
    ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
    // Use names and ensure unique to protect against duplicates
    Set<String> names = new LinkedHashSet<>(
            SpringFactoriesLoader.loadFactoryNames(type, classLoader));
    List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
            classLoader, args, names);
    AnnotationAwareOrderComparator.sort(instances);
    return instances;
}

可以看到慢逾，加載異常收集器與上面初始化器和監(jiān)聽器如出一轍立倍，不做過多闡述。

上下文前置處理侣滩、廣播`ApplicationPreparedEvent`事件

// 上下文前置處理（執(zhí)行ApplicationContextInitializer系列初始化器口注、加載資源、廣播ApplicationPreparedEvent）
prepareContext(context, environment, listeners, applicationArguments,
            printedBanner);

private void prepareContext(ConfigurableApplicationContext context,
        ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
        ApplicationArguments applicationArguments, Banner printedBanner) {
    // 關(guān)聯(lián)上下文和環(huán)境
    context.setEnvironment(environment);
    //
    postProcessApplicationContext(context);
    // 去重并排序前面獲取好的ApplicationContextInitializer初始化器胜卤，執(zhí)行初始化
    applyInitializers(context);
    // 遍歷前面設(shè)置好的SpringApplicationRunListener疆导，但并沒有發(fā)布（目前什么都沒做，貌似為了以后擴展）
    listeners.contextPrepared(context);
    if (this.logStartupInfo) {
        logStartupInfo(context.getParent() == null);
        logStartupProfileInfo(context);
    }

    // Add boot specific singleton beans
    // 添加啟動特定的單例bean
    ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
    beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
    if (printedBanner != null) {
        beanFactory.registerSingleton("springBootBanner", printedBanner);
    }

    if (beanFactory instanceof DefaultListableBeanFactory) {
        ((DefaultListableBeanFactory) beanFactory)
                .setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
    }
    // Load the sources
    // 加載sources資源
    Set<Object> sources = getAllSources();
    Assert.notEmpty(sources, "Sources must not be empty");

    load(context, sources.toArray(new Object[0]));
    // 廣播ApplicationPreparedEvent
    listeners.contextLoaded(context);
}

在啟動上下文之前葛躏，會調(diào)用前面初始化好的ApplicationContextInitializer接口實現(xiàn)類澈段，當(dāng)然也包含我們自定義的，所以我們可以自定義初始化器舰攒，在上下文啟動前做一些操作败富。之后會廣播ApplicationPreparedEvent事件，通知SpringApplicationRunListener監(jiān)聽器ConfigurableApplicationContext上下文已準備好（框架中用listeners.contextLoaded(context);方法廣播了ApplicationPreparedEvent事件摩窃，而ApplicationLoadedEvent事件并沒有發(fā)布兽叮，感覺這里以后還會變動芬骄。。鹦聪。）账阻。

刷新上下文

// 刷新上下文（）
refreshContext(context);

private void refreshContext(ConfigurableApplicationContext context) {
    refresh(context);
    if (this.registerShutdownHook) {
        try {
            context.registerShutdownHook();
        }
        catch (AccessControlException ex) {
            // Not allowed in some environments.
        }
    }
}

發(fā)布`ApplicationStartedEvent`事件

// 遍歷前面設(shè)置的ConfigurableApplicationContext監(jiān)聽器，發(fā)布ApplicationStartedEvent
listeners.started(context);

public void started(ConfigurableApplicationContext context) {
    for (SpringApplicationRunListener listener : this.listeners) {
        listener.started(context);
    }
}

@Override
public void started(ConfigurableApplicationContext context) {
    context.publishEvent(
            new ApplicationStartedEvent(this.application, this.args, context));
}

發(fā)布ApplicationStartedEvent事件泽本，通知　SpringApplicationRunListener系列監(jiān)聽器ConfigurableApplicationContext上下文已啟動完成淘太，Spring Bean 已初始化完成。

回調(diào)實現(xiàn)了`ApplicationRunner`或`CommandLineRunner`接口的`Runners`

// 按順序回調(diào)實現(xiàn)了ApplicationRunner或CommandLineRunner接口的Runners
callRunners(context, applicationArguments);

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);
        }
    }
}

這里是有順序的规丽，ApplicationRunner的實現(xiàn)類優(yōu)先于CommandLineRunner的實現(xiàn)類被回調(diào)

發(fā)布`ApplicationReadyEvent`事件

try {
    // 遍歷前面設(shè)置好的SpringApplicationRunListener監(jiān)聽器蒲牧，發(fā)布ApplicationReadyEvent
    listeners.running(context);
}

public void running(ConfigurableApplicationContext context) {
    for (SpringApplicationRunListener listener : this.listeners) {
        listener.running(context);
    }
}

@Override
public void running(ConfigurableApplicationContext context) {
    context.publishEvent(
            new ApplicationReadyEvent(this.application, this.args, context));
}

發(fā)布ApplicationReadyEvent事件,通知SpringApplicationRunListener系列監(jiān)聽器ConfigurableApplicationContext上下文已經(jīng)在運行，整個容器已經(jīng)準備好冰抢。

發(fā)布`ExitCodeEvent`和`ApplicationFailedEvent`事件和異常收集器收集異常信息

catch (Throwable ex) {
    handleRunFailure(context, ex, exceptionReporters, listeners);
    throw new IllegalStateException(ex);
}

private void handleRunFailure(ConfigurableApplicationContext context,
        Throwable exception,
        Collection<SpringBootExceptionReporter> exceptionReporters,
        SpringApplicationRunListeners listeners) {
    try {
        try {
            handleExitCode(context, exception);
            if (listeners != null) {
                listeners.failed(context, exception);
            }
        }
        finally {
            reportFailure(exceptionReporters, exception);
            if (context != null) {
                context.close();
            }
        }
    }
    catch (Exception ex) {
        logger.warn("Unable to close ApplicationContext", ex);
    }
    ReflectionUtils.rethrowRuntimeException(exception);
}

如果啟動過程中出現(xiàn)異常可柿，springboot將會發(fā)布ExitCodeEvent事件通知上下文停止或重啟忆畅，并發(fā)布ApplicationFailedEvent事件通知SpringApplicationRunListener系列監(jiān)聽器钉鸯，最后SpringBootExceptionReporter異常收集器收集打印異常。

總結(jié)

SpringBoot啟動過程大致脈絡(luò)

準備階段
- 參數(shù)初始化
- 推斷應(yīng)用類型
- 加載ApplicationContextInitializer系列初始化器
- 加載ApplicationListener系列監(jiān)聽器
- 推斷應(yīng)用入口類（main函數(shù)所在類）
運行階段
- 初始化容器啟動計時器燥狰，開始計時
- 初始化上下文ConfigurableApplicationContext、異常收集器
- 配置系統(tǒng)參數(shù)"java.awt.headless"
- 獲取SpringApplicationRunListener系列監(jiān)聽器
- 遍歷所有SpringApplicationRunListener系列監(jiān)聽器煞抬，廣播ApplicationStartingEvent
- 處理args參數(shù)
- 準備環(huán)境（創(chuàng)建革答、配置碟嘴、綁定環(huán)境边败、廣播ApplicationEnvironmentPreparedEvent）
- 配置忽略Bean信息
- 打印Banner
- 根據(jù)應(yīng)用類型創(chuàng)建上下文
- 獲取SpringBootExceptionReporter系列異常收集器
- 上下文前置處理（執(zhí)行ApplicationContextInitializer系列初始化器排截、加載資源智政、廣播ApplicationPreparedEvent）
- 刷新上下文
- 啟動完成，打印用時
- 遍歷前面設(shè)置的ConfigurableApplicationContext監(jiān)聽器页慷，發(fā)布ApplicationStartedEvent
- 回調(diào)實現(xiàn)了ApplicationRunner或CommandLineRunner接口的Runners
- 遍歷前面設(shè)置好的SpringApplicationRunListener監(jiān)聽器酒繁，發(fā)布ApplicationReadyEvent

至此彰居，整個SpringBoot項目已經(jīng)啟動完成，我們可以看到溶握，整個過程中Spring的事件驅(qū)動機制起著舉足輕重的作用杯缺，有了這個機制我們可以知曉容器的啟動過程，并且可以監(jiān)聽到某些事件睡榆，對容器中我們關(guān)心的實例做進一步處理萍肆，我們深入理解事件驅(qū)動機制很有必要，它將幫助我們更好的理解和使用這個Spring框架體系胀屿。如果想要文中中文版SpringBoot注釋源碼塘揣，可以在我的github下載，如果發(fā)現(xiàn)哪里寫的不對宿崭，煩請留言通知我亲铡。

更多信息可以關(guān)注我的個人博客：逸竹小站

也歡迎關(guān)注我的公眾號：yizhuxiaozhan，二維碼：

公眾號二維碼

最后編輯于：2020.02.22 20:43:36

?著作權(quán)歸作者所有,轉(zhuǎn)載或內(nèi)容合作請聯(lián)系作者

人面猴
序言：七十年代末劳曹，一起剝皮案震驚了整個濱河市奴愉，隨后出現(xiàn)的幾起案子，更是在濱河造成了極大的恐慌铁孵，老刑警劉巖锭硼，帶你破解...
沈念sama閱讀 221,198評論 6贊 514
死咒
序言：濱河連續(xù)發(fā)生了三起死亡事件，死亡現(xiàn)場離奇詭異蜕劝，居然都是意外死亡檀头，警方通過查閱死者的電腦和手機，發(fā)現(xiàn)死者居然都...
沈念sama閱讀 94,334評論 3贊 398
救了他兩次的神仙讓他今天三更去死
文/潘曉璐我一進店門岖沛，熙熙樓的掌柜王于貴愁眉苦臉地迎上來暑始，“玉大人，你說我怎么就攤上這事婴削±染担” “怎么了？”我有些...
開封第一講書人閱讀 167,643評論 0贊 360
道士緝兇錄：失蹤的賣姜人
文/不壞的土叔我叫張陵唉俗，是天一觀的道長嗤朴。經(jīng)常有香客問我配椭，道長，這世上最難降的妖魔是什么雹姊？我笑而不...
開封第一講書人閱讀 59,495評論 1贊 296
?港島之戀（遺憾婚禮）
正文為了忘掉前任股缸，我火速辦了婚禮，結(jié)果婚禮上吱雏，老公的妹妹穿的比我還像新娘敦姻。我一直安慰自己，他們只是感情好歧杏，可當(dāng)我...
茶點故事閱讀 68,502評論 6贊 397
惡毒庶女頂嫁案：這布局不是一般人想出來的
文/花漫我一把揭開白布镰惦。她就那樣靜靜地躺著，像睡著了一般得滤。火紅的嫁衣襯著肌膚如雪陨献。梳的紋絲不亂的頭發(fā)上，一...
開封第一講書人閱讀 52,156評論 1贊 308
城市分裂傳說
那天懂更，我揣著相機與錄音，去河邊找鬼急膀。笑死沮协，一個胖子當(dāng)著我的面吹牛，可吹牛的內(nèi)容都是我干的卓嫂。我是一名探鬼主播慷暂，決...
沈念sama閱讀 40,743評論 3贊 421
雙鴛鴦連環(huán)套：你想象不到人心有多黑
文/蒼蘭香墨我猛地睜開眼，長吁一口氣：“原來是場噩夢啊……” “哼晨雳！你這毒婦竟也來了行瑞？” 一聲冷哼從身側(cè)響起，我...
開封第一講書人閱讀 39,659評論 0贊 276
萬榮殺人案實錄
序言：老撾萬榮一對情侶失蹤餐禁，失蹤者是張志新（化名）和其女友劉穎血久，沒想到半個月后，有當(dāng)?shù)厝嗽跇淞掷锇l(fā)現(xiàn)了一具尸體帮非，經(jīng)...
沈念sama閱讀 46,200評論 1贊 319
?護林員之死
正文獨居荒郊野嶺守林人離奇死亡氧吐，尸身上長有42處帶血的膿包…… 初始之章·張勛以下內(nèi)容為張勛視角年9月15日...
茶點故事閱讀 38,282評論 3贊 340
?白月光啟示錄
正文我和宋清朗相戀三年，在試婚紗的時候發(fā)現(xiàn)自己被綠了末盔。大學(xué)時的朋友給我發(fā)了我未婚夫和他白月光在一起吃飯的照片筑舅。...
茶點故事閱讀 40,424評論 1贊 352
活死人
序言：一個原本活蹦亂跳的男人離奇死亡，死狀恐怖陨舱，靈堂內(nèi)的尸體忽然破棺而出翠拣，到底是詐尸還是另有隱情，我是刑警寧澤游盲，帶...
沈念sama閱讀 36,107評論 5贊 349
?日本核電站爆炸內(nèi)幕
正文年R本政府宣布误墓，位于F島的核電站蛮粮，受9級特大地震影響，放射性物質(zhì)發(fā)生泄漏优烧。R本人自食惡果不足惜蝉揍，卻給世界環(huán)境...
茶點故事閱讀 41,789評論 3贊 333
男人毒藥：我在死后第九天來索命
文/蒙蒙一、第九天我趴在偏房一處隱蔽的房頂上張望畦娄。院中可真熱鬧又沾，春花似錦、人聲如沸熙卡。這莊子的主人今日做“春日...
開封第一講書人閱讀 32,264評論 0贊 23
一樁弒父案，背后竟有這般陰謀
文/蒼蘭香墨我抬頭看了看天上的太陽驳癌。三九已至滑燃，卻和暖如春，著一層夾襖步出監(jiān)牢的瞬間颓鲜，已是汗流浹背表窘。一陣腳步聲響...
開封第一講書人閱讀 33,390評論 1贊 271
情欲美人皮
我被黑心中介騙來泰國打工，沒想到剛下飛機就差點兒被人妖公主榨干…… 1. 我叫王不留甜滨，地道東北人乐严。一個月前我還...
沈念sama閱讀 48,798評論 3贊 376
代替公主和親
正文我出身青樓，卻偏偏與公主長得像衣摩，于是被迫代替她去往敵國和親昂验。傳聞我的和親對象是個殘疾皇子，可洞房花燭夜當(dāng)晚...
茶點故事閱讀 45,435評論 2贊 359

SpringBoot源碼分析之---SpringBoot項目啟動類SpringApplication淺析

源碼版本說明

SpringBoot入口類

SpringApplication初始化階段

推斷應(yīng)用類型

加載ApplicationContextInitializer系列初始化器

加載ApplicationListener系列監(jiān)聽器

推斷應(yīng)用入口類

運行階段

獲取SpringApplicationRunListener系列監(jiān)聽器

廣播ApplicationStartingEvent事件

準備環(huán)境疗锐、廣播ApplicationEnvironmentPreparedEvent事件

開始打印Banner

根據(jù)應(yīng)用類型創(chuàng)建上下文

獲取SpringBootExceptionReporter系列異常收集器

上下文前置處理侣滩、廣播ApplicationPreparedEvent事件