SpringBoot流程解析（一）

目录

注解

SpringApplication::SpringApplication

壹

贰

叁

肆

伍

陆

---

好久没看SpringBoot了，复习一下，温故而知新。

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

注解

大白话教会你@SpringBootApplication中如何进行自动配置_明天一定.的博客-CSDN博客_springbootapplication自动配置一文帮你理解springBoot自动配置原理，快点卷起来https://blog.csdn.net/wai_58934/article/details/122049950?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522166157703016782390538284%2522%252C%2522scm%2522%253A%252220140713.130102334.pc%255Fblog.%2522%257D&request_id=166157703016782390538284&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2~blog~first_rank_ecpm_v1~rank_v31_ecpm-2-122049950-null-null.nonecase&utm_term=springboot&spm=1018.2226.3001.4450简单来说的作用：

• 声明是一个spring应用程序配置类
• 把这个类加载到ioc容器中去，完成包扫描
• 导入配置类
• 根据定义的扫描路径，把符合扫描规则的类装配到spring容器中

SpringApplication::SpringApplication

除了注解，就只有一行代码

SpringApplication.run(SecurityApplication.class,args);

 我们来分析run方法，点进去看到

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

我们先分析

(new SpringApplication(primarySources))

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
        // 壹
		this.resourceLoader = resourceLoader;
		Assert.notNull(primarySources, "PrimarySources must not be null");
        // 贰
		this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
        // 叁
		this.webApplicationType = WebApplicationType.deduceFromClasspath();
        // 肆
		setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
        // 伍
		setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
        // 陆
		this.mainApplicationClass = deduceMainApplicationClass();
	}

壹

配置resourceLoader

贰

配置主启动类

叁

判断当前应用程序的类型。

static WebApplicationType deduceFromClasspath() {
		if (ClassUtils.isPresent(WEBFLUX_INDICATOR_CLASS, null) && !ClassUtils.isPresent(WEBMVC_INDICATOR_CLASS, null)
				&& !ClassUtils.isPresent(JERSEY_INDICATOR_CLASS, null)) {
			return WebApplicationType.REACTIVE;
		}
		for (String className : SERVLET_INDICATOR_CLASSES) {
			if (!ClassUtils.isPresent(className, null)) {
				return WebApplicationType.NONE;
			}
		}
		return WebApplicationType.SERVLET;
	}

根据Class是否存在而去判断应用程序类型（反射）。

肆

获取初始化器的实例对象

(Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class)

往代码里边点，走到

loadSpringFactories(classLoader).getOrDefault(factoryTypeName, Collections.emptyList());

 第一步：我们来看loadSpringFactories(classLoader)

 主要从META-INF/spring.factories中获取需要加载的类（去重），并且最后放入缓存中

	private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
		MultiValueMap<String, String> result = cache.get(classLoader);
		if (result != null) {
			return result;
		}

		try {
			Enumeration<URL> urls = (classLoader != null ?
					classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
					ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
			result = new LinkedMultiValueMap<>();
			while (urls.hasMoreElements()) {
				URL url = urls.nextElement();
				UrlResource resource = new UrlResource(url);
				Properties properties = PropertiesLoaderUtils.loadProperties(resource);
				for (Map.Entry<?, ?> entry : properties.entrySet()) {
					String factoryTypeName = ((String) entry.getKey()).trim();
					for (String factoryImplementationName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {
						result.add(factoryTypeName, factoryImplementationName.trim());
					}
				}
			}
			cache.put(classLoader, result);
			return result;
		}
		catch (IOException ex) {
			throw new IllegalArgumentException("Unable to load factories from location [" +
					FACTORIES_RESOURCE_LOCATION + "]", ex);
		}
	}

 第二步我们来看getOrDefault(factoryTypeName, Collections.emptyList()):

从map中取出来key为ApplicationContextInitializer的value。

伍

获取监听器的实例对象

分析过程同上

陆

找到当前应用程序的主类，开始执行