spring-boot-starter-web依赖**

查看spring-boot-starter-web依赖文件源码，核心代码具体如下

<dependencies>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter</artifactId>
    <version>2.2.2.RELEASE</version>
    <scope>compile</scope>
  </dependency>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-json</artifactId>
    <version>2.2.2.RELEASE</version>
    <scope>compile</scope>
  </dependency>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-tomcat</artifactId>
    <version>2.2.2.RELEASE</version>
    <scope>compile</scope>
  </dependency>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-validation</artifactId>
    <version>2.2.2.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>5.2.2.RELEASE</version>
    <scope>compile</scope>
  </dependency>
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-webmvc</artifactId>
    <version>5.2.2.RELEASE</version>
    <scope>compile</scope>
  </dependency>
</dependencies>

从上述代码可以发现，spring-boot-starter-web依赖启动器的主要作用是提供Web开发场景所需的底层所有依赖

正是如此，在pom.xml中引入spring-boot-starter-web依赖启动器时，就可以实现Web场景开发，而不需要额外导入Tomcat服务器以及其他Web依赖文件等。当然，这些引入的依赖文件的版本号还是由spring-boot-starter-parent父依赖进行的统一管理。