一、简述
Springboot启动是通过Application启动类实现 - springboot启动分为注解和启动方法两个过程
@SpringBootApplication(@b@ exclude = {MongoAutoConfiguration.class, MongoDataAutoConfiguration.class},@b@ scanBasePackages = {"com.test.data"})@b@@EnableCaching@b@public class DataApplication {@b@ public static void main(String[] args) {@b@ SpringApplication.run(DataApplication.class); @b@ }@b@}二、@SpringBootApplicaiton注解
进入@SpringBootApplication注解内，可见@SpringBootApplication=@SpringCofiguration+@EnableConfiguration+@ComponentScan
@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@Documented@Inherited@SpringBootConfiguration@EnableAutoConfiguration@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class), @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })public @interface SpringBootApplication {...}2.1 @SpringBootConfiguration -- Spring IOC容器配置类进入@SpringBootConfiguration注解内如下，可见@SpringBootConfiguration本身也是一种配置（@Configuration）@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@Documented@Configuration@Indexedpublic @interface SpringBootConfiguration {@Configuration的作用（定义一些可以被自动加载IOC容器的配置bean）：@Configuration标注在类上，配置spring容器（应用上下文）。进入@Configuration注解里使用@Component，返回类型都会直接注册为bean(任何一个标注了@Bean的方法，其返回值都将作为一个bean定义注册到Spring的IOC容器)，所以@Configuration具有和@Component作用，因此@CompoenntScan都能处理@Configuration注解的类@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@Documented@Componentpublic @interface Configuration {...} demo如下，使用@Configuration可以将配置文件中配置信息（比如下例中启动环境env 邮件收件人 emailTo等）作为元素组成的bean，在spring启动时自动注入到IOC容器中。@Configuration@Datapublic class EmailConfig { @Value("${spring.profiles.active}") public String env; @Value("${email.to}") public String emailTo; @Value("${email.from}") public String emailFrom;} 2.2 @EnableAutoConfiguration--（开启自动配置,使用@import將所有符合自动配置条件的bean定义加载到IOC容器）进入@EnableAutoConfiguration如下,使用@Import将所有满足条件的bean自动加载到IOC容器 @Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@Documented@Inherited@AutoConfigurationPackage@Import(AutoConfigurationImportSelector.class)public @interface EnableAutoConfiguration {...} 2.3 @ComponentScan-（开启自动自动扫描，默认扫描SpringApplication的run方法里的class所在的包路径下文件） 自动扫描并加载符合条件的组件或者bean定义。默认扫描SpringApplication的run方法里class所有的包路径下文件三.启动方法 .run()
启动方法分为创建springApplicaiton实例和执行run方法
3.1创建SpringApplication实例 - SpringApplication实例创建过程如下图所示。
3.2 执行run()方法 - 包括环境准备、创建IOC容器、配置IOC容器基本信息、刷新上下文信息等。具体查看参考 https://www.cnblogs.com/enhance/p/17024932.html
public ConfigurableApplicationContext run(String... args) {@b@ long startTime = System.nanoTime();@b@ DefaultBootstrapContext bootstrapContext = createBootstrapContext();@b@ ConfigurableApplicationContext context = null;@b@ configureHeadlessProperty();@b@ SpringApplicationRunListeners listeners = getRunListeners(args);@b@ listeners.starting(bootstrapContext, this.mainApplicationClass);@b@ try {@b@ ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);@b@ ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);@b@ configureIgnoreBeanInfo(environment);@b@ Banner printedBanner = printBanner(environment);@b@ context = createApplicationContext();@b@ context.setApplicationStartup(this.applicationStartup);@b@ prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);@b@ refreshContext(context);@b@ afterRefresh(context, applicationArguments);@b@ Duration timeTakenToStartup = Duration.ofNanos(System.nanoTime() - startTime);@b@ if (this.logStartupInfo) {@b@ new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), timeTakenToStartup);@b@ }@b@ listeners.started(context, timeTakenToStartup);@b@ callRunners(context, applicationArguments);@b@ }@b@ catch (Throwable ex) {@b@ handleRunFailure(context, ex, listeners);@b@ throw new IllegalStateException(ex);@b@ }@b@ try {@b@ Duration timeTakenToReady = Duration.ofNanos(System.nanoTime() - startTime);@b@ listeners.ready(context, timeTakenToReady);@b@ }@b@ catch (Throwable ex) {@b@ handleRunFailure(context, ex, null);@b@ throw new IllegalStateException(ex);@b@ }@b@ return context;@b@ }四、启动过程图
