SpringBoot启动流程

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

• SpringBoot启动会执行 SpringApplication.run(FirstSpringApplication.class);即 执行run方法，将启动类作为参数传递过去。

public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
        /**
         * new SpringApplication(primarySources) 环境的初始化和其他的准备工作
         * run就是启动容器，以及自动配置类中的服务器的服务
         */
        return new SpringApplication(primarySources).run(args);
    }

• 这里有两个流程：
  1. new SpringApplication(primarySources)
  2. run(args)

new SpringApplication(primarySources)流程

public SpringApplication(Class<?>... primarySources) {
        this(null, primarySources);
    }

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();
        //设置初始化器
        setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
        //设置容器监听器
        setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
        this.mainApplicationClass = deduceMainApplicationClass();
    }

其中最主要的两端代码

    //设置初始化器
    setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
    //设置容器监听器
    setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));

设置初始化容器

1. getSpringFactoriesInstances(ApplicationContextInitializer.class)

    private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
            ClassLoader classLoader = getClassLoader();
            // Use names and ensure unique to protect against duplicates
            // 获取当前的所有的classpath下spring.factories里面的name
            Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
            //根据上一步name通过反射获取实例对象
            List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
            AnnotationAwareOrderComparator.sort(instances);
            return instances;


   private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
        MultiValueMap<String, String> result = (MultiValueMap)cache.get(classLoader);
        if (result != null) {
            return result;
        } else {
            try {
                Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");
                LinkedMultiValueMap result = new LinkedMultiValueMap();

                while(urls.hasMoreElements()) {
                    URL url = (URL)urls.nextElement();
                    UrlResource resource = new UrlResource(url);
                    Properties properties = PropertiesLoaderUtils.loadProperties(resource);
                    Iterator var6 = properties.entrySet().iterator();

                    while(var6.hasNext()) {
                        Entry<?, ?> entry = (Entry)var6.next();
                        String factoryClassName = ((String)entry.getKey()).trim();
                        String[] var9 = StringUtils.commaDelimitedListToStringArray((String)entry.getValue());
                        int var10 = var9.length;

                        for(int var11 = 0; var11 < var10; ++var11) {
                            String factoryName = var9[var11];
                            result.add(factoryClassName, factoryName.trim());
                        }
                    }
                }

                cache.put(classLoader, result);
                return result;
            } catch (IOException var13) {
                throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", var13);
            }
        }
    }

2. setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class))