分析springboot启动流程

准备

最简单的springboot项目代码，如下：

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

代码分析

按照代码执行顺序记录流程。

1、SpringApplication类

在启动类EurekaApplication中执行的是SpringApplication类的静态方法run。第一个参数是启动类的class对象，第二个参数是启动main方法的参数。

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);
}

1.1、创建SpringApplication对象

创建SpringApplication对象的主逻辑如下。其中resourceLoader为null，primarySources是EurekaApplication的class对象。

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
	this.resourceLoader = resourceLoader;
	Assert.notNull(primarySources, "PrimarySources must not be null");
	this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
	this.webApplicationType = deduceWebApplicationType();
	setInitializers((Collection) getSpringFactoriesInstances(
			ApplicationContextInitializer.class));
	setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
	this.mainApplicationClass = deduceMainApplicationClass();
}

1.1.1、设置SpringApplication对象的属性

resourceLoader 为null。
primarySources 集合只有启动类一个元素。
webApplicationType ：应用的启动类型，三种，具体参考WebApplicationType类。一般是SERVLET（The application should run as a servlet-based web application and should start an embedded servlet web server.）
setInitializers：初始化springboot应用启动过程中后续要用到的容器启动类。初始化完毕后，设置为SpringApplication的属性initializers。启动类如下图：
setListeners：初始化监听器。初始化完毕后，设置为SpringApplication的属性listeners。监听器如下图：
确定mainApplicationClass，即为main方法被执行的EurekaApplication类。判断当前线程的栈帧中，类的方法名是main的类。

至此，SpringApplication类创建完毕。

1.2、SpringApplication对象执行run方法

public ConfigurableApplicationContext run(String... args) {
	StopWatch stopWatch = new StopWatch();
	stopWatch.start();
	ConfigurableApplicationContext context = null;
	Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
	configureHeadlessProperty();
	SpringApplicationRunListeners listeners = getRunListeners(args);
	listeners.starting();
	try {
		ApplicationArguments applicationArguments = new DefaultApplicationArguments(
				args);
		ConfigurableEnvironment environment = prepareEnvironment(listeners,
				applicationArguments);
		configureIgnoreBeanInfo(environment);
		Banner printedBanner = printBanner(environment);
		context = createApplicationContext();
		exceptionReporters = getSpringFactoriesInstances(
				SpringBootExceptionReporter.class,
				new Class[] { ConfigurableApplicationContext.class }, context);
		prepareContext(context, environment, listeners, applicationArguments,
				printedBanner);
		refreshContext(context);
		afterRefresh(context, applicationArguments);
		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;
}

1.2.1、创建StopWatch对象并执行start方法

StopWatch：Simple stop watch, allowing for timing of a number of tasks, exposing(暴露; 揭露; 显露; 曝光) total running time and running time for each named task.
默认的名字是空字符串。
start方法是简单的属性赋值。

1.2.2、定义上下文对象和启动异常记录集合

ConfigurableApplicationContext context = null;
Collection exceptionReporters = new ArrayList<>();

1.2.3、设置系统属性

configureHeadlessProperty();

1.2.4、创建事件传播监听器并启动

SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting(); // 不知道具体干了什么

springboot启动流程分析