SpringBoot 源码分析 (主线源码分析) (一)-CFANZ编程社区

文章目录

1.SpringBoot启动的入口

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

当我们启动一个SpringBoot项目的时候，入口程序就是main方法，而在main方法中就执行了一个run方法。

@SpringBootApplication
public class Main {
    public static void main(String[] args){
        SpringApplication app = new SpringApplication(Main.class);
        app.run(args);
    }
}

2.run方法

SpringApplication#run()
然后我们进入run()方法中看。代码比较简单

	public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
		// 调用重载的run方法，将传递的Class对象封装为了一个数组
		return run(new Class<?>[] { primarySource }, args);
	}

调用了重载的一个run()方法，将我们传递进来的类对象封装为了一个数组，仅此而已。我们再进入run()方法。

	public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
		return new SpringApplication(primarySources).run(args);
	}

在该方法中创建了一个SpringApplication对象。同时调用了SpringApplication对象的run方法。这里的逻辑有分支，先看下SpringApplication的构造方法中的逻辑

3.SpringApplication构造器

	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 = WebApplicationType.deduceFromClasspath();
		this.bootstrapRegistryInitializers = getBootstrapRegistryInitializersFromSpringFactories();
		setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
		setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
		this.mainApplicationClass = deduceMainApplicationClass();
	}

推断当前项目的类型
加载配置在spring.factories文件中的ApplicationContextInitializer中的类型并实例化后存储在了initializers中。
和2的步骤差不多，完成监听器的初始化操作，并将实例化的监听器对象存储在了listeners成员变量中
通过StackTrace反推main方法所在的Class对象

4.run方法深度解析

接下来我们在回到SpringApplication.run()方法中。

	public ConfigurableApplicationContext run(String... args) {
		StopWatch stopWatch = new StopWatch();
		stopWatch.start();
		DefaultBootstrapContext bootstrapContext = createBootstrapContext();
		ConfigurableApplicationContext context = null;
		configureHeadlessProperty();
		SpringApplicationRunListeners listeners = getRunListeners(args);
		listeners.starting(bootstrapContext, this.mainApplicationClass);
		try {
			ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
			ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
			configureIgnoreBeanInfo(environment);
			Banner printedBanner = printBanner(environment);
			context = createApplicationContext();
			context.setApplicationStartup(this.applicationStartup);
			prepareContext(bootstrapContext, 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, listeners);
			throw new IllegalStateException(ex);
		}

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