1. 父專案

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.0.RELEASE</version>
    </parent>

	它的父專案是

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-dependencies</artifactId>
        <version>2.1.0.RELEASE</version>
        <relativePath>../../spring-boot-dependencies</relativePath>
    </parent>
	這個父專案管理所有依賴的版本，被稱為spring boot版本仲裁中心
	以後導依賴預設使用這裡的版本，不需要自己寫，沒有的才需要自己寫版本
 

2. starter 啟動器

starter 是為滿足某一場景的一系列依賴集合

官方介紹

Starters are a set of convenient dependency descriptors that you can include in your application. You get a one-stop shop for all the Spring and related technologies that you need without having to hunt through sample code and copy-paste loads of dependency descriptors. For example, if you want to get started using Spring and JPA for database access, include the spring-boot-starter-data-jpa dependency in your project.

The starters contain a lot of the dependencies that you need to get a project up and running quickly and with a consistent, supported set of managed transitive dependencies.

3. Spring Boot入口程式

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

@SpringBootApplication

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration // 註解標註這是一個spring boot配置類
@EnableAutoConfiguration // 開啟自動配置功能
@ComponentScan(
    excludeFilters = {@Filter(
    type = FilterType.CUSTOM,
    classes = {TypeExcludeFilter.class}
), @Filter(
    type = FilterType.CUSTOM,
    classes = {AutoConfigurationExcludeFilter.class}
)}
)
public @interface SpringBootApplication {

@SpringBootConfiguration 註解標註這是一個spring boot配置類

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
public @interface SpringBootConfiguration {
}

@EnableAutoConfiguration

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
// 將被註解類所在包及子包下的元件掃描到spring容器，相當於以前spring裡面的註解配置類
@AutoConfigurationPackage 
// 完成功能的自動配置，如以前要自己做的spring mvc配置
@Import({AutoConfigurationImportSelector.class}) 
public @interface EnableAutoConfiguration {