SpringBoot 启动方法run()源码赏析

入口
通常一个简单的SpringBoot基础项目我们会有如下代码

@SpringBootApplication
@RestController
@RequestMapping("/")
public class Application {

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

}

值得关注的有SpringApplication.run以及注解@SpringBootApplication

run方法

public ConfigurableApplicationContext run(String... args) {
	    // 秒表
		StopWatch stopWatch = new StopWatch();
		stopWatch.start();
		ConfigurableApplicationContext context = null;
		Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
		configureHeadlessProperty();
		// 获取监听器
		SpringApplicationRunListeners listeners = getRunListeners(args);
		// 监听器启动
		listeners.starting();
		try {
		    // application 启动参数列表
			ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
			ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
			// 配置忽略的bean信息
			configureIgnoreBeanInfo(environment);
			Banner printedBanner = printBanner(environment);
			// 创建应用上下文
			context = createApplicationContext();
			exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
					new Class[] { ConfigurableApplicationContext.class }, context);
		    // 准备上下文，装配bean
			prepareContext(context, environment, listeners, applicationArguments, printedBanner);
			// 上下文刷新
			refreshContext(context);
			// 刷新后做什么
			afterRefresh(context, applicationArguments);
			stopWatch.stop();
			if (this.logStartupInfo) {
				new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
			}
			// 监听器开始了
			listeners.started(context);
			// 唤醒
			callRunners(context, applicationArguments);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, listeners);
			throw new IllegalStateException(ex);
		}

		try {
		    // 监听器正式运行
			listeners.running(context);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, null);
			throw new IllegalStateException(ex);
		}
		return context;
	}

getRunListeners

获取监听器

private SpringApplicationRunListeners getRunListeners(String[] args) {
		Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };
		// 获取  Spring Factory 实例对象
		return new SpringApplicationRunListeners(logger,
				getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args));
	}


	private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
		ClassLoader classLoader = getClassLoader();
		// Use names and ensure unique to protect against duplicates
		// 读取 spring.factories
		Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
		// 创建SpringFactory实例
		List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
		/**
		 * 排序 {@link Ordered}
		 */
		AnnotationAwareOrderComparator.sort(instances);
		return instances;
	}

createSpringFactoriesInstances

 @SuppressWarnings("unchecked")
   private <T> List<T> createSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes,
   		ClassLoader classLoader, Object[] args, Set<String> names) {
       // 初始化
   	List<T> instances = new ArrayList<>(names.size());
   	for (String name : names) {
   		try {
   		    // 通过名字创建类的class对象
   			Class<?> instanceClass = ClassUtils.forName(name, classLoader);
   			Assert.isAssignable(type, instanceClass);
   			// 构造器获取
   			Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes);
   			// 创建具体实例
   			T instance = (T) BeanUtils.instantiateClass(constructor, args);
   			// 加入实例表中
   			instances.add(instance);
   		}
   		catch (Throwable ex) {
   			throw new IllegalArgumentException("Cannot instantiate " + type + " : " + name, ex);
   		}
   	}
   	return instances;
   }

printBanner

private Banner printBanner(ConfigurableEnvironment environment) {
		if (this.bannerMode == Banner.Mode.OFF) {
			return null;
		}
		ResourceLoader resourceLoader = (this.resourceLoader != null) ? this.resourceLoader
				: new DefaultResourceLoader(getClassLoader());
		// 创建打印器
		SpringApplicationBannerPrinter bannerPrinter = new SpringApplicationBannerPrinter(resourceLoader, this.banner);
		if (this.bannerMode == Mode.LOG) {
		    // 输出
			return bannerPrinter.print(environment, this.mainApplicationClass, logger);
		}
        // 输出
		return bannerPrinter.print(environment, this.mainApplicationClass, System.out);
	}
	Banner print(Environment environment, Class<?> sourceClass, PrintStream out) {
		Banner banner = getBanner(environment);
		banner.printBanner(environment, sourceClass, out);
		return new PrintedBanner(banner, sourceClass);
	}

最终输出内容类：org.springframework.boot.SpringBootBanner

class SpringBootBanner implements Banner {

	private static final String[] BANNER = { "", "  .   ____          _            __ _ _",
			" /\\\\ / ___'_ __ _ _(_)_ __  __ _ \\ \\ \\ \\", "( ( )\\___ | '_ | '_| | '_ \\/ _` | \\ \\ \\ \\",
			" \\\\/  ___)| |_)| | | | | || (_| |  ) ) ) )", "  '  |____| .__|_| |_|_| |_\\__, | / / / /",
			" =========|_|==============|___/=/_/_/_/" };

	private static final String SPRING_BOOT = " :: Spring Boot :: ";

	private static final int STRAP_LINE_SIZE = 42;

	@Override
	public void printBanner(Environment environment, Class<?> sourceClass, PrintStream printStream) {
		for (String line : BANNER) {
			printStream.println(line);
		}
		String version = SpringBootVersion.getVersion();
		version = (version != null) ? " (v" + version + ")" : "";
		StringBuilder padding = new StringBuilder();
		while (padding.length() < STRAP_LINE_SIZE - (version.length() + SPRING_BOOT.length())) {
			padding.append(" ");
		}

		printStream.println(AnsiOutput.toString(AnsiColor.GREEN, SPRING_BOOT, AnsiColor.DEFAULT, padding.toString(),
				AnsiStyle.FAINT, version));
		printStream.println();
	}

}

希望通过本篇对于springboot启动方法的解读，让大家对springboot底层有了一个大致了解，只分析了主要方法，希望对大家有帮助
对于技术交流和探讨，或者想跳槽加薪的可以关注我的公众号，免费领取面试资料和技术书籍

本文地址：https://blog.csdn.net/weixin_44302240/article/details/110499108