springboot启动方式_启动会启动仪式

@SpringBootApplication
public class SpringBootAnalysisApplication {

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

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
        @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
        @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })

    public static ConfigurableApplicationContext run(Object source, String... args) {
        //这里我们的第一个参数source的值是：SpringBootAnalysisApplication.class，在重载的run方法中将
        //传入的SpringBootAnalysisApplication.class封装成了数组，也就是说我们可以调用重载的run方法，传入一个Object[]，第二个参数是一个可变参数，是我们传入的启动参数。
        return run(new Object[] { source }, args);
    }

    public static ConfigurableApplicationContext run(Object[] sources, String[] args) {
        return new SpringApplication(sources).run(args);
    }

    public SpringApplication(Object... sources) {
        //调用initialize方法进行一些初始化的动作。
        initialize(sources);
    }

    private void initialize(Object[] sources) {
        if (sources != null && sources.length > 0) {
            //如果传入的sources有值的话，将Object[]对象转换为List。这里的sources是
            //private final Set<Object> sources = new LinkedHashSet<Object>();
            //是一个Set集合。
            this.sources.addAll(Arrays.asList(sources));
        }
        //判断是否是web环境 1)
        this.webEnvironment = deduceWebEnvironment();
        //加载ApplicationContextInitializer类型的对象 2)
        setInitializers((Collection) getSpringFactoriesInstances(
                ApplicationContextInitializer.class));
        //加载ApplicationListener类型的对象 3)
        setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
        //寻找启动主类 4)
        this.mainApplicationClass = deduceMainApplicationClass();
    }

    private boolean deduceWebEnvironment() {
    //private static final String[] WEB_ENVIRONMENT_CLASSES = { "javax.servlet.Servlet",
    // "org.springframework.web.context.ConfigurableWebApplicationContext" };
    //WEB_ENVIRONMENT_CLASSES是一个数组内容如上
        for (String className : WEB_ENVIRONMENT_CLASSES) {
            //如果加载不到任何一个类就返回false
            if (!ClassUtils.isPresent(className, null)) {
                return false;
            }
        }
        return true;
    }

 private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type) { 
      return getSpringFactoriesInstances(type, new Class<?>[] {}); } private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) { //线程上下文加载器 ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); // Use names and ensure unique to protect against duplicates Set<String> names = new LinkedHashSet<String>( //关键代码 SpringFactoriesLoader.loadFactoryNames(type, classLoader)); //根据上一步获取到的类，创建实例对象,这里没什么多说的 List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names); //排序也没有什么多说的 AnnotationAwareOrderComparator.sort(instances); return instances; }

    public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
//获取要加载的类的全限定名这里是org.springframework.context.ApplicationContextInitializer
String factoryClassName = factoryClass.getName();
try {
//加载资源 从加载的是哪个资源呢？META-INF/spring.factories这个文件
//注意这里会加载所有类路径下的/META-INF/spring.factories，在Spring的相关jar包中基本上都有这个文件存在，当然也可以在自己的工程中自定义。
Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
List<String> result = new ArrayList<String>();
while (urls.hasMoreElements()) {
URL url = urls.nextElement();
Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
//获取键为前面获取到的全限定类名的值,多个值用 , 分割
String factoryClassNames = properties.getProperty(factoryClassName);
//用, 分割上面获取到的值 
result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
}
return result;
}
}

    private Class<?> deduceMainApplicationClass() {
try {
//获取运行时方法调用栈的信息 
StackTraceElement[] stackTrace = new RuntimeException().getStackTrace();
for (StackTraceElement stackTraceElement : stackTrace) {
//找到方法调用链上方法名为main的类
if ("main".equals(stackTraceElement.getMethodName())) {
//返回main方法所在的类对象这里是 com.zkn.springboot.analysis.SpringBootAnalysisApplication
return Class.forName(stackTraceElement.getClassName());
}
}
}
return null;
}