Spring注解之：@SpringBootApplication

@SpringBootApplication

 is
a convenience annotation that adds all of the following:

@Configuration

 tags
the class as a source of bean definitions for theapplication context. 

@EnableAutoConfiguration

 tells
Spring Boot to start adding beans based on classpath settings,other beans,and
various property settings.

Normally you would add 

@EnableWebMvc

 for
a Spring MVC app, but Spring Boot adds it automatically when it sees spring-webmvc on the classpath. This flags the application as a web application and activates key behaviors such as
setting up a 

DispatcherServlet

.
（DispatcherServlet是什么可看这里 http://blog.csdn.net/zhouhuakang/article/details/50643034）

@ComponentScan

 tells
Spring to look for other components, configurations, and services in the the 

hello

 package,
allowing it to find the 

HelloController

.

参考
1.https://spring.io/guides/gs/spring-boot/