springboot框架学习积累---SpringBoot源码剖析之依赖管理_springboot源码是如何加载依赖的-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_39314972/article/details/108424263

本文深入剖析SpringBoot中依赖管理机制，重点介绍spring-boot-starter-parent如何统一版本管理，及spring-boot-starter-web如何通过依赖传递引入所需jar包。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

springboot框架学习积累—SpringBoot源码剖析之依赖管理

1. 为什么导入dependency时不需要指定版本(spring-boot-starter-parent父依赖启动器进行版本统一管理)

Spring Boot程序中有两个核心的依赖`spring-boot-starter-parent`,`spring-boot-starter-web`

spring-boot-starter-parent依赖

<parent> 
		<groupId>org.springframework.boot</groupId> 
		<artifactId>spring-boot-starter-parent</artifactId> 
		<version>2.2.2.RELEASE</version> 
		<relativePath/> <!-- lookup parent from repository -->
</parent>

进入spring-boot-starter-parent并查看,发现底层有一个父依赖spring-boot-dependencies,核心具体代码如下

  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-dependencies</artifactId>
    <version>2.2.2.RELEASE</version>
    <relativePath>../../spring-boot-dependencies</relativePath>
  </parent>

里面的properties标签：定义了编码集的格式,jdk版本，maven编译版本

	  <properties>
	    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
	    <java.version>1.8</java.version>
	    <resource.delimiter>@</resource.delimiter>
	    <maven.compiler.source>${java.version}</maven.compiler.source>
	    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
	    <maven.compiler.target>${java.version}</maven.compiler.target>
 	 </properties>

看下面build标签中includes标签，引入外部配置文件,加载顺序是先yml文件，后yaml文件，最后properties文件,所以说properties文件的优先级最高

<resources>
  <resource>
    <filtering>true</filtering>
    <directory>${basedir}/src/main/resources</directory>
    <includes>
      <include>**/application*.yml</include>
      <include>**/application*.yaml</include>
      <include>**/application*.properties</include>
    </includes>
  </resource>
  ...
</resources>

所以说，在SpringBoot的父工程中都做了什么？1. 进行编码的默认设置，JDK的默认版本设置，==2. == 引入一些配置文件，==3. == 插件管理

继续查看spring-boot-dependencies底层源码，核心代码如下,其中dependencyManagement指定版本，进行版本的锁定，properties只是声明版本

<properties>
    <activemq.version>5.15.11</activemq.version>
    ...
    <solr.version>8.2.0</solr.version>
    <mysql.version>8.0.18</mysql.version>
    <kafka.version>2.3.1</kafka.version>
    <spring-amqp.version>2.2.2.RELEASE</spring-amqp.version>
    <spring-restdocs.version>2.0.4.RELEASE</spring-restdocs.version>
    <spring-retry.version>1.2.4.RELEASE</spring-retry.version>
    <spring-security.version>5.2.1.RELEASE</spring-security.version>
    <spring-session-bom.version>Corn-RELEASE</spring-session-bom.version>
    <spring-ws.version>3.0.8.RELEASE</spring-ws.version>
    <sqlite-jdbc.version>3.28.0</sqlite-jdbc.version>
    <sun-mail.version>${jakarta-mail.version}</sun-mail.version>
    <tomcat.version>9.0.29</tomcat.version>
    <thymeleaf.version>3.0.11.RELEASE</thymeleaf.version>
    <thymeleaf-extras-data-attribute.version>2.0.1
    </thymeleaf-extras-dataattribute.version>
            ...
</properties>
<dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot</artifactId>
        <version>2.2.9.RELEASE</version>
      </dependency>
      ...
      <dependency>
        <groupId>org.apache.activemq</groupId>
        <artifactId>activemq-amqp</artifactId>
        <version>${activemq.version}</version>
  	  </dependency>
 	  ...
  	</dependencies> 
</dependencyManagement>

在这里插入图片描述

2. spring-boot-starter-parent父依赖启动器的主要作用是进行版本统一管理，那么项目运行jar包是从何而来(依赖传递)

查看spring-boot-starter-webׁ依赖文件源码发现，SpringBoot项目通过依赖spring-boot-starter-webׁ会自动引入SpringMVC的依赖，并且使用tomcat作为内嵌容器，spring-boot-starter-webׁ又依赖了web开发场景所需要的底层的所有依赖(spring-webmvc ...),通过依赖传递的方式来使用项目运行需要的jar包

  <dependencies>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter</artifactId>
      <version>2.2.9.RELEASE</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-json</artifactId>
      <version>2.2.9.RELEASE</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-tomcat</artifactId>
      <version>2.2.9.RELEASE</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-validation</artifactId>
      <version>2.2.9.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>5.2.8.RELEASE</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-webmvc</artifactId>
      <version>5.2.8.RELEASE</version>
      <scope>compile</scope>
    </dependency>
  </dependencies>