SpringBoot版本 [2.1.5.RELEASE]

启动类中主要是run方法和@SpringBootApplication注解

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

@SpringBootApplication注解:
- @SpringBootConfiguration
- @EnableAutoConfiguration
- @ComponentScan
run()方法:
- SpringApplication初始化
- 执行run(UserApplication.class, args)

@SpringBootApplication注解:

@SpringBootConfiguration

点进去是用@Configuration

@EnableAutoConfiguration

package org.springframework.boot.autoconfigure;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.context.annotation.Import;

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited

//指定包规则
@AutoConfigurationPackage 

//AutoConfigurationImportSelector 把@Configuration配置都加载到当前容器中
@Import({AutoConfigurationImportSelector.class})

public @interface EnableAutoConfiguration {
    String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";

    Class<?>[] exclude() default {};

    String[] excludeName() default {};
}

@ComponentScan

自定义过滤器，指定扫描路径

SpringApplication初始化

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
        this.sources = new LinkedHashSet();
        this.bannerMode = Mode.CONSOLE;
        this.logStartupInfo = true;
        this.addCommandLineProperties = true;
        this.addConversionService = true;
        this.headless = true;
        this.registerShutdownHook = true;
        this.additionalProfiles = new HashSet();
        this.isCustomEnvironment = false;
        this.resourceLoader = resourceLoader;
        Assert.notNull(primarySources, "PrimarySources must not be null");
        this.primarySources = new LinkedHashSet(Arrays.asList(primarySources));
        
        //判断webApplicationType应用类型reactive响应式或servlet
        this.webApplicationType = WebApplicationType.deduceFromClasspath();
        
        //查找META-INF/spring.factories中的key值为ApplicationContextInitializer实现类。在getSpringFactoriesInstances方法中进行读取(先走缓存，无缓存读文件)、实例化
        this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));
        
        //查找META-INF/spring.factories中的key值为ApplicationListener实现类。在getSpringFactoriesInstances方法中进行读取(先走缓存，无缓存读文件)、实例化
        this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));
        //设置主类class
        this.mainApplicationClass = this.deduceMainApplicationClass();
    }

run(String… args)

public ConfigurableApplicationContext run(String... args) {
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        ConfigurableApplicationContext context = null;
        Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList();
        this.configureHeadlessProperty();
        
        //加载监听器，查找META-INF/spring.factories中的key值为SpringApplicationRunListener实现类。在getSpringFactoriesInstances方法中进行读取(先走缓存，无缓存读文件)、实例化
        SpringApplicationRunListeners listeners = this.getRunListeners(args);
        //发布ApplicationStartingEvent，SpringApplication开始启动
        listeners.starting();

        Collection exceptionReporters;
        try {
        	//封装入参
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            //准备环境
            ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
            this.configureIgnoreBeanInfo(environment);
            //打印banner
            Banner printedBanner = this.printBanner(environment);
            //创建上下文
            context = this.createApplicationContext();
            //SpringBootExceptionReporter 异常报告处理
            exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
            //上下文准备完成
            this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
            //刷新上下文
            this.refreshContext(context);
            this.afterRefresh(context, applicationArguments);
            stopWatch.stop();
            if (this.logStartupInfo) {
                (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
            }
			//上下文已经刷新
            listeners.started(context);
            //调用所有runner
            this.callRunners(context, applicationArguments);
        } catch (Throwable var10) {
            this.handleRunFailure(context, var10, exceptionReporters, listeners);
            throw new IllegalStateException(var10);
        }

        try {
        	//running()方法，通知所有的监听器，容器正在启动
            listeners.running(context);
            return context;
        } catch (Throwable var9) {
            this.handleRunFailure(context, var9, exceptionReporters, (SpringApplicationRunListeners)null);
            throw new IllegalStateException(var9);
        }
    }