Springboot启动流程剖析

一、前言

Spring Framework的强大扩展点，赋予了对象丰富的生命周期；但是其配置繁琐，而且不太灵活，什么都需要自己来配置引入；简直就是优秀的架构，构造的噩梦。就在这过程中，官方Springboot以快速构建突破了这一痛点，也被开发者赋予Spring急行军的称号。通过下面3点我们将了解简单的Springboot：

本章不会涉及到springboot的自动装配，仅针对启动流程！！！

1.Springboot项目搭建
2.游走Springboot启动流程源码
3.Springboot启动流程图

二、Springboot急行军项目搭建

启动入口

@SpringBootApplication
public class SpringApplication {
    public static void main(String[] args) {
        org.springframework.boot.SpringApplication.run(SpringApplication.class,args);
    }
}

依赖
maven

<!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter</artifactId>
    <version>2.3.5.RELEASE</version>
</dependency>

gradle

// https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter
implementation group: 'org.springframework.boot', name: 'spring-boot-starter', version: '2.3.5.RELEASE'

执行输出结果

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.3.5.RELEASE)

2021-06-23 13:44:14.090 INFO  [main]  c.x.c.SpringApplication - [logStarting,55] - Starting SpringApplication on localhost with PID 49608 (/Users/wangcai/appData/development/projects/java/self/springboothome/cache/build/classes/java/main started by wangcai in /Users/wangcai/appData/development/projects/java/self/springboothome)
2021-06-23 13:44:14.096 INFO  [main]  c.x.c.SpringApplication - [logStartupProfileInfo,651] - No active profile set, falling back to default profiles: default
2021-06-23 13:44:14.646 INFO  [main]  c.x.c.SpringApplication - [logStarted,61] - Started SpringApplication in 0.832 seconds (JVM running for 1.884)

三、游走Springboot启动流程源码

简单了解@SpringBootApplication
@SpringBootApplication

完成扫描和启动自动装配

深入理解Springboot启动流程
SpringApplication

最终会进入主构造

真正的启动流程（只会针对重要的来进行说明）

1⃣️、创建合适的应用上下文


2⃣️、准备上下文

监听上下文、注册实例（run入口传入的类）

3⃣️、刷新上下文

四、Springboot启动流程图