项目构建
我们采用maven构建SpringBoot工程，首先创建一个maven工程，对应的pom文件如下：
1.8 org.springframework.boot spring-boot-starter-parent 1.5.7.RELEASE org.springframework.boot spring-boot-starter-web org.springframework.boot spring-boot-maven-plugin
创建Application.java
package com.ysl;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;@SpringBootApplicationpublic class Application { public static void main(String[] args){ SpringApplication.run(Application.class,args); }} 运行main方法，运行结果如下：
. ____ _ __ _ _ /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \ \\/ ___)| |_)| | | | | || (_| | ) ) ) ) ' |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot :: (v1.5.7.RELEASE)2018-03-03 10:28:24.028 INFO 6358 --- [ main] com.ysl.Application : Starting Application on master with PID 6358 (/home/workspace/springboottest/target/classes started by ysl in /home/workspace/springboottest)2018-03-03 10:28:24.038 INFO 6358 --- [ main] com.ysl.Application : No active profile set, falling back to default profiles: default2018-03-03 10:28:24.218 INFO 6358 --- [ main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@1b37288: startup date [Sat Mar 03 10:28:24 CST 2018]; root of context hierarchy2018-03-03 10:28:27.001 INFO 6358 --- [ main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat initialized with port(s): 8080 (http)2018-03-03 10:28:27.025 INFO 6358 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]2018-03-03 10:28:27.026 INFO 6358 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet Engine: Apache Tomcat/8.5.202018-03-03 10:28:27.141 INFO 6358 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext2018-03-03 10:28:27.142 INFO 6358 --- [ost-startStop-1] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 2936 ms2018-03-03 10:28:27.294 INFO 6358 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean : Mapping servlet: 'dispatcherServlet' to [/]2018-03-03 10:28:27.299 INFO 6358 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'characterEncodingFilter' to: [/*]2018-03-03 10:28:27.300 INFO 6358 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]2018-03-03 10:28:27.300 INFO 6358 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'httpPutFormContentFilter' to: [/*]2018-03-03 10:28:27.300 INFO 6358 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'requestContextFilter' to: [/*]2018-03-03 10:28:27.669 INFO 6358 --- [ main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@1b37288: startup date [Sat Mar 03 10:28:24 CST 2018]; root of context hierarchy2018-03-03 10:28:27.755 INFO 6358 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error],produces=[text/html]}" onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)2018-03-03 10:28:27.756 INFO 6358 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error]}" onto public org.springframework.http.ResponseEntity > org.springframework.boot.autoconfigure.web.BasicErrorController.error(javax.servlet.http.HttpServletRequest)2018-03-03 10:28:27.795 INFO 6358 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]2018-03-03 10:28:27.796 INFO 6358 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]2018-03-03 10:28:27.835 INFO 6358 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]2018-03-03 10:28:28.143 INFO 6358 --- [ main] o.s.j.e.a.AnnotationMBeanExporter : Registering beans for JMX exposure on startup2018-03-03 10:28:28.252 INFO 6358 --- [ main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8080 (http)2018-03-03 10:28:28.261 INFO 6358 --- [ main] com.ysl.Application : Started Application in 5.148 seconds (JVM running for 5.974) spring boot已经启动，内嵌tomcat容器，监听为8080端口，一个springboot程序就这么简单的被创建了。
@SpringBootApplication 注解
SpringBootApplication注解的源码如下：
@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 @interface SpringBootApplication { @AliasFor( annotation = EnableAutoConfiguration.class, attribute = "exclude" ) Class [] exclude() default {}; @AliasFor( annotation = EnableAutoConfiguration.class, attribute = "excludeName" ) String[] excludeName() default {}; @AliasFor( annotation = ComponentScan.class, attribute = "basePackages" ) String[] scanBasePackages() default {}; @AliasFor( annotation = ComponentScan.class, attribute = "basePackageClasses" ) Class [] scanBasePackageClasses() default {};} @Configuration : 表示Application作为sprig配置文件存在
@EnableAutoConfiguration: 启动spring boot内置的自动配置 @ComponentScan : 扫描bean，路径为Application类所在package以及package下的子路径，这里为 com.ysl，在spring boot中bean都放置在该路径已经子路径下。 构建REST工程
上面的操作连个HelloWorld都没有出来，远远满不足我们的需求。在com.ysl下创建子包controller，在该包下创建TestController.java，内容如下：
package com.ysl.controller;import org.springframework.web.bind.annotation.Mapping;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController;@RestControllerpublic class TestController { @RequestMapping("/") public String home(){ return "hello,springboot"; }} 重新启动程序，访问http:localhost:8080，得到结果：hello,springboot