spring-boot之starter

1.如何理解starter

1.1.模塊管理，自動加載Bean到IOC

1.Starter 是 Spring Boot 中的一個非常重要的概念，Starter相當於模塊，
 它能將模塊所需的依賴整合起來並對模塊內的Bean根據環境（條件）進行自動配置。
 使用者只需要依賴相應功能的 Starter，無需做過多的配置和依賴，SpringBoot 就能自動掃描並加載相應的模塊。

通俗理解

1.比如我們進行spring的web項目開發，這個時候，可能我們沒辦法知道需要加載那些jar或者沒法十分清楚需要的jar包
  這個時候spring-bootstarter-web這個starter就給我們一鍵式的整理了所有的需要jar
  這樣能夠更快捷的簡化開發，提升開發進度，避免不必要的開發調試jar包依賴的工作，將需要的Bean自動加載到IOC容器之中

1.2.通過spring-boot-starter-web去理解starter概念

從右邊我們可以看出來，spring-boot-starter-web 本質上就是將web開發需要的所有的jar包依賴給導入進來了

<?xml version="1.0" encoding="UTF-8"?>
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <modelVersion>4.0.0</modelVersion>
  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starters</artifactId>
    <version>2.2.6.RELEASE</version>
  </parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
  <version>2.2.6.RELEASE</version>
  <name>Spring Boot Web Starter</name>
  <description>Starter for building web, including RESTful, applications using Spring
		MVC. Uses Tomcat as the default embedded container</description>
  <url>https://projects.spring.io/spring-boot/#/spring-boot-parent/spring-boot-starters/spring-boot-starter-web</url>
  <organization>
    <name>Pivotal Software, Inc.</name>
    <url>https://spring.io</url>
  </organization>
  <licenses>
    <license>
      <name>Apache License, Version 2.0</name>
      <url>https://www.apache.org/licenses/LICENSE-2.0</url>
    </license>
  </licenses>
  <developers>
    <developer>
      <name>Pivotal</name>
      <email>[e-mail]</email>
      <organization>Pivotal Software, Inc.</organization>
      <organizationUrl>https://www.spring.io</organizationUrl>
    </developer>
  </developers>
  <scm>
    <connection>scm:git:git://github.com/spring-projects/spring-boot.git</connection>
    <developerConnection>scm:git:ssh://[e-mail]/spring-projects/spring-boot.git</developerConnection>
    <url>https://github.com/spring-projects/spring-boot</url>
  </scm>
  <issueManagement>
    <system>Github</system>
    <url>https://github.com/spring-projects/spring-boot/issues</url>
  </issueManagement>
  <dependencies>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter</artifactId>
      <version>2.2.6.RELEASE</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-json</artifactId>
      <version>2.2.6.RELEASE</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-tomcat</artifactId>
      <version>2.2.6.RELEASE</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-validation</artifactId>
      <version>2.2.6.RELEASE</version>
      <scope>compile</scope>
      <exclusions>
        <exclusion>
          <artifactId>tomcat-embed-el</artifactId>
          <groupId>org.apache.tomcat.embed</groupId>
        </exclusion>
      </exclusions>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-web</artifactId>
      <version>5.2.5.RELEASE</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-webmvc</artifactId>
      <version>5.2.5.RELEASE</version>
      <scope>compile</scope>
    </dependency>
  </dependencies>
</project>