SpringBoot的三种启动方式
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springBoot 是什么
springboot 是一个框架，它依赖于spring，在过去我们使用spring项目的时候，需要大量各种繁琐的配置文件才能让spring跑起来，但自从有了springboot之后，它简化了使用方式，做到了无xml文件的配置即可运行，最大的特点是让配置文件变得简单，得益于自身的自动装配功能，部署也变得更简单（springboot内置web容器服务器tomcat），加上热部署后，可以快速开发和运行一个项目；
spring大家都知道，boot是启动的意思。所以，spring boot其实就是一个启动spring项目的一个工具而已，总而言之，springboot 是一个服务于框架的框架；
Spring Boot的核心功能
1、 可独立运行的Spring项目：Spring Boot可以以jar包的形式独立运行。
2、 内嵌的Servlet容器：Spring Boot可以选择内嵌Tomcat、Jetty或者Undertow，无须以war包形式部署项目。
3、 简化的Maven配置：Spring提供推荐的基础 POM 文件来简化Maven 配置。
4、 自动配置Spring：Spring Boot会根据项目依赖来自动配置Spring 框架，极大地减少项目要使用的配置。
5、 提供生产就绪型功能：提供可以直接在生产环境中使用的功能，如性能指标、应用信息和应用健康检查。
6、 无代码生成和xml配置：Spring Boot不生成代码。完全不需要任何xml配置即可实现Spring的所有配置。
第一种启动方式 @EnableAutoConfiguration
@EnableAutoConfiguration 作用
开启自动装配，帮助SpringBoot应用将所有符合条件的@Configuration配置都加载到当前SpringBoot，并创建对应配置类的Bean，并把该Bean实体交给IoC容器进行管理。
在使用springboot之前，我们需要先导入相关的jar包
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.0.8.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.spring</groupId>
<artifactId>springBoot-demo1</artifactId>
<version>1.0-SNAPSHOT</version>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
</dependencies>
</project>新建文件 IndexController.java
package com.spring;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@EnableAutoConfiguration
@RestController
public class IndexController
// 访问路径 http://localhost:8080/index
@RequestMapping("/index")
public String index()
System.out.println("我进来了");
return "index controller";
public static void main(String[] args)
// 启动springboot
SpringApplication.run(IndexController.class,args);
运行main方法，后即可启动项目了
. ____ _ __ _ _
/\\\\ / ___'_ __ _ _(_)_ __ __ _ \\ \\ \\ \\
( ( )\\___ | '_ | '_| | '_ \\/ _` | \\ \\ \\ \\
\\\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.0.8.RELEASE)
2021-06-03 20:37:26.010 INFO 942 --- [ main] com.spring.IndexController : Starting IndexController on xiexindongdeMacBook-Pro.local with PID 942 (/Users/yexindong/Documents/java/java_project/springBootdemo1/target/classes started by yexindong in /Users/yexindong/Documents/java/java_project)
2021-06-03 20:37:26.014 INFO 942 --- [ main] com.spring.IndexController : No active profile set, falling back to default profiles: default
2021-06-03 20:37:26.064 INFO 942 --- [ main] ConfigServletWebServerApplicationContext : Refreshing org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@105fece7: startup date [Thu Jun 03 20:37:26 CST 2021]; root of context hierarchy
2021-06-03 20:37:27.329 INFO 942 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
2021-06-03 20:37:27.365 INFO 942 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2021-06-03 20:37:27.365 INFO 942 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet Engine: Apache Tomcat/8.5.37
2021-06-03 20:37:27.375 INFO 942 --- [ost-startStop-1] o.a.catalina.core.AprLifecycleListener : The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: [/Users/yexindong/Library/Java/Extensions:/Library/Java/Extensions:/Network/Library/Java/Extensions:/System/Library/Java/Extensions:/usr/lib/java:.]
2021-06-03 20:37:27.474 INFO 942 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2021-06-03 20:37:27.474 INFO 942 --- [ost-startStop-1] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 1413 ms
2021-06-03 20:37:27.520 INFO 942 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean : Servlet dispatcherServlet mapped to [/]
2021-06-03 20:37:27.523 INFO 942 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'characterEncodingFilter' to: [/*]
2021-06-03 20:37:27.523 INFO 942 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2021-06-03 20:37:27.523 INFO 942 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'httpPutFormContentFilter' to: [/*]
2021-06-03 20:37:27.523 INFO 942 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'requestContextFilter' to: [/*]
2021-06-03 20:37:27.619 INFO 942 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2021-06-03 20:37:27.750 INFO 942 --- [ main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@105fece7: startup date [Thu Jun 03 20:37:26 CST 2021]; root of context hierarchy
2021-06-03 20:37:27.805 INFO 942 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "[/index]" onto public java.lang.String com.spring.IndexController.index()
2021-06-03 20:37:27.808 INFO 942 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "[/error]" onto public org.springframework.http.ResponseEntity<java.util.Map<java.lang.String, java.lang.Object>> org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.error(javax.servlet.http.HttpServletRequest)
2021-06-03 20:37:27.808 INFO 942 --- [ 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.servlet.error.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)
2021-06-03 20:37:27.825 INFO 942 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2021-06-03 20:37:27.825 INFO 942 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2021-06-03 20:37:27.938 INFO 942 --- [ main] o.s.j.e.a.AnnotationMBeanExporter : Registering beans for JMX exposure on startup
2021-06-03 20:37:27.986 INFO 942 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
2021-06-03 20:37:27.990 INFO 942 --- [ main] com.spring.IndexController : Started IndexController in 2.649 seconds (JVM running for 3.063)
2021-06-03 20:37:40.475 INFO 942 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring FrameworkServlet 'dispatcherServlet'
2021-06-03 20:37:40.475 INFO 942 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : FrameworkServlet 'dispatcherServlet': initialization started
2021-06-03 20:37:40.491 INFO 942 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : FrameworkServlet 'dispatcherServlet': initialization completed in 16 ms
在浏览器输入网址访问 controller ：http://localhost:8080/index 页面结果如下：
控制台也输出了打印的内容，是不是很简单呢？
第二种启动方式 @ComponentScan
@ComponentScan() 注解作用
根据定义的扫描路径，将符合规则的类加载到spring容器中，比如在类中加入了以下注解 @Controller、@Service、@Mapper 、@Component、@Configuration 等等；
接下来我们测试一下，创建启动类 App.java
package com.spring.controller;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.context.annotation.ComponentScan;
@EnableAutoConfiguration // 开启自动装配
@ComponentScan("com.spring.controller")
public class App
public static void main(String[] args)
// 启动springboot
SpringApplication.run(App.class,args);
控制层 OrderController.java
package com.spring.controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class OrderController
@RequestMapping("/order")
public String order()
System.out.println("我进来了 order controller 的 index 方法");
return "order controller";
启动后访问接口 http://localhost:8080/order
控制台打印结果
第三种方式 @SpringBootApplication
@SpringBootApplication 注解作用
标注这是一个springboot的应用，被标注的类是一个主程序， SpringApplication.run(App.class, args);传入的类App.class必须是被@SpringBootApplication标注的类。
@SpringBootApplication是一个组合注解，组合了其他相关的注解，点进去注解后我们可以看到，这个注解集成了以上2种启动方式的注解；在这里的 @ComponentScan() 注解有一堆东西，它的作用是 将主配置类所在包及其下面所有后代包的所有注解扫描；
SpringBootApplication 使用起来更加简单，只需要一个注解即可完成，
package com.spring.controller;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class App
public static void main(String[] args)
// 启动springboot
SpringApplication.run(App.class,args);
启动后控制台打印的信息
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