Spring Boot启动过程源码阅读

入口

代码部分

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

注解@SpringBootApplication

@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 {

	@AliasFor(annotation = EnableAutoConfiguration.class)
	Class<?>[] exclude() default {};

	@AliasFor(annotation = EnableAutoConfiguration.class)
	String[] excludeName() default {};

	@AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
	String[] scanBasePackages() default {};

	@AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")
	Class<?>[] scanBasePackageClasses() default {};

}

元注解说明

@Target注解类型
@Retention注解生命周期，包括source，class，runtime
@Documented注解被javadoc收录
@Inherited 表示被@SpringBootApplication修饰的类，其子类可以继承@SpringBootApplication注解

框架定义的注解

@SpringBootConfiguration同@Configuration注解，对应xml中的beans标签
@EnableAutoConfiguration启用SpringBoot自动配置上下文，自动扫描加载子目录下的bean
@ComponentScan

入口实现

构造SpringApplication代码

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);
}

//构造方法，构造SpringApplication
@SuppressWarnings({ "unchecked", "rawtypes" })
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
    //设置资源加载类，null
    this.resourceLoader = resourceLoader;
    Assert.notNull(primarySources, "PrimarySources must not be null");
    //初始化主要资源集
    this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
    //判断使用的是Servlet模式，WebFlux模式或者NONE
    this.webApplicationType = WebApplicationType.deduceFromClasspath();
    //设置需要初始化组件
    setInitializers((Collection) getSpringFactoriesInstances(
        ApplicationContextInitializer.class));
    //设置监听器
    setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
    //推断主入口类
    this.mainApplicationClass = deduceMainApplicationClass();
}

启动SpringApplication

public ConfigurableApplicationContext run(String... args) {
    //启动计时器
    StopWatch stopWatch = new StopWatch();
    stopWatch.start();
    ConfigurableApplicationContext context = null;
    Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
    //设置java.awt.headless参数（无界面）
    configureHeadlessProperty();
    //加载并启动监听器（初始官方默认就EventPublishListener）
    SpringApplicationRunListeners listeners = getRunListeners(args);
    listeners.starting();
    try {
        //加载启动参数
        ApplicationArguments applicationArguments = new DefaultApplicationArguments(
            args);
        //准备环境
        ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
        //
        configureIgnoreBeanInfo(environment);
        //打印banner图标
        Banner printedBanner = printBanner(environment);
        context = createApplicationContext();
        exceptionReporters = getSpringFactoriesInstances(
            SpringBootExceptionReporter.class,
            new Class[] { ConfigurableApplicationContext.class }, context);
        //准备上下文：
        prepareContext(context, environment, listeners, applicationArguments,
                       printedBanner);
        //刷新上下文
        refreshContext(context);
        //
        afterRefresh(context, applicationArguments);
        //计时结束
        stopWatch.stop();
        if (this.logStartupInfo) {
            new StartupInfoLogger(this.mainApplicationClass)
                .logStarted(getApplicationLog(), stopWatch);
        }
        listeners.started(context);
        callRunners(context, applicationArguments);
    }
    catch (Throwable ex) {
        handleRunFailure(context, ex, exceptionReporters, listeners);
        throw new IllegalStateException(ex);
    }

    try {
        listeners.running(context);
    }
    catch (Throwable ex) {
        handleRunFailure(context, ex, exceptionReporters, null);
        throw new IllegalStateException(ex);
    }
    return context;
}

准备上下文

private void prepareContext(ConfigurableApplicationContext context,
			ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
			ApplicationArguments applicationArguments, Banner printedBanner) {
    //设置环境参数：激活哪个profiles，加载application.properties下配置的Property
    context.setEnvironment(environment);
    postProcessApplicationContext(context);
    applyInitializers(context);
    listeners.contextPrepared(context);
    if (this.logStartupInfo) {
        logStartupInfo(context.getParent() == null);
        logStartupProfileInfo(context);
    }
    // Add boot specific singleton beans
    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
    Set<Object> sources = getAllSources();
    Assert.notEmpty(sources, "Sources must not be empty");
    load(context, sources.toArray(new Object[0]));
    listeners.contextLoaded(context);
}

Spring Boot启动过程源码阅读

入口

入口实现

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